JP5234218B1 - Light emitting diode element - Google Patents

Abstract

An object of the present invention is to provide a GaN-based light emitting diode element that is excellent in luminous efficiency and suitable as an excitation light source for white LEDs.
A GaN-based light-emitting diode element includes an n-type conductive m-plane GaN substrate, a light-emitting diode structure formed using a GaN-based semiconductor on a front surface of the m-plane GaN substrate, and the m-plane GaN substrate. It has a flat portion provided on the back surface of the surface GaN substrate and an n-side ohmic electrode formed on the flat portion of the rough processed portion, and a forward current applied to the light emitting diode element is 20 mA. In this case, the forward voltage is 4.0 V or less.
[Selection] Figure 1

Description

The present invention relates to a light-emitting diode element, and more particularly to a GaN-based light-emitting diode element having a light-emitting structure formed using a GaN-based semiconductor. A GaN-based semiconductor is a compound semiconductor represented by the general formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), and is a nitride semiconductor. It is also called a nitride compound semiconductor.

  Semiconductor light emitting devices having a double hetero pn junction type light emitting structure formed using a GaN-based semiconductor on an m-plane GaN substrate are known (Non-Patent Documents 1 to 4).

  Non-Patent Documents 1 to 3 disclose light-emitting diode elements. In any element, an n-side ohmic electrode is formed on an n-type Si-doped GaN layer formed by epitaxial growth on an m-plane GaN substrate. Is formed. Non-Patent Document 4 discloses a laser diode element in which an n-side ohmic electrode is formed on the back surface of an m-plane GaN substrate. The threshold current of this laser diode element is 36 mA at the time of CW driving, 28 mA at the time of pulse driving, and the threshold voltage is about 7 to 8V.

  In a light emitting device having a light emitting structure formed on a GaN substrate, it is said that it is difficult to form a good n-side ohmic electrode on the back surface of the GaN substrate (Patent Documents 1 to 6). Therefore, in the method described in Patent Document 2, the contact resistance of the n-side ohmic electrode formed on the back surface is reduced by polishing the back surface of the GaN substrate with a polishing agent having a particle diameter of 10 μm or more. It has been. In the method described in Patent Document 3, for the same purpose, the back surface of the GaN substrate is roughened by wet etching or dry etching. On the other hand, according to Patent Document 4, a damaged layer is formed when the back surface is ground, lapped or polished in order to reduce the thickness of the GaN substrate, which inhibits the formation of a good ohmic electrode. . Therefore, in the method described in Patent Document 4, the back surface of the polished GaN substrate is shaved by dry etching or wet etching. However, Patent Document 5 describes that this purpose cannot be achieved by wet etching. In the method described in Patent Document 6, the contact resistance between the GaN substrate and the n-side ohmic electrode is reduced by dry-etching the back surface of the GaN substrate and scraping off the portion containing crystal defects generated by mechanical polishing. It has been. In addition, the knowledge and invention described in these Patent Documents 1 to 6 basically relate to a c-plane GaN substrate.

  An electrode pad formed using a metal material on the element surface is essential for a light emitting diode as a part to which a power feeding member such as a metal wire, a metal bump, or solder is bonded. Since the electrode pad does not have optical transparency, a light emitting diode in which the current flowing through the light emitting structure is concentrated in a portion that is a shadow of the electrode pad when viewed from the light extraction direction has low light emission efficiency. This is because the light generated at this site is shielded and absorbed by the electrode pad and cannot be extracted efficiently outside the device. Therefore, to prevent the current from concentrating on this part, a high resistance film (insulating film) or a high resistance region is provided as a current block structure between the electrode pad and the light emitting structure to control the path of the current flowing in the element. (Patent Documents 7 to 9).

JP-A-11-340571 JP 2002-16312 A JP 2004-71657 A JP 2003-51614 A JP 2003-347660 A Japanese Patent Laid-Open No. 2004-6718 JP-A-1-151274 JP-A-7-193279 Japanese Patent Laid-Open No. 10-229219

Kuniyoshi Okamoto et al., Japanese Journal of Applied Physics, Vol. 45, No. 45, 2006, pp. L1197-L1199 Mathew C. Schmidt et al., JapaneseJournalof Applied Physics, Vol. 46, No. 7, 2007, pp. L126-L128 Shih-Pang Chang et al., Journal of The Electrochemical Society, 157 (5) H501-H503 (2010) Kuniyoshi Okamoto et al., Japanese Journal of Applied Physics, Vol. 46, No. 9, 2007, pp. L187-L189

A GaN-based light-emitting diode element in which a light-emitting structure is formed on an m-plane GaN substrate does not cause QCSE (Quantum-confined Stark effect), and therefore a white LED that is required to have a small variation in emission wavelength with an increase in applied current Suitable for excitation light source. However, if the heat generation amount of the light emitting diode element is large or its heat dissipation is not good, the temperature of the phosphor largely fluctuates due to the heat emitted by the light emitting diode element, and the expected effect cannot be obtained. . Further, a light emitting diode element having a large amount of heat generation and poor heat dissipation has a low luminous efficiency because its own temperature greatly increases as the applied current is increased.

This invention is made | formed in view of the said situation, The main objective is to provide the GaN-type light emitting diode element suitable for the excitation light source for white LED.
Another object of the present invention is to provide a GaN-based light emitting diode device with improved luminous efficiency, having an n-side electrode formed on the back surface of an m-plane GaN substrate.
Still another object of the present invention is to provide a method of manufacturing a GaN-based light emitting diode device having a low contact resistance n-side electrode formed on the back surface of an m-plane GaN substrate.

According to one aspect of the present invention, the following GaN-based light emitting diode device is provided.
(1) An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. A GaN-based light emitting diode device having a forward voltage of 4.0 V or less when a forward current applied to the light emitting diode device is 20 mA.
(2) An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. A GaN-based light emitting diode element having a forward voltage of 4.5 V or less when a forward current applied to the light emitting diode element is 60 mA.
(3) An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. A GaN-based light emitting diode element having a forward voltage of 5.0 V or less when a forward current applied to the light emitting diode element is 120 mA.
(4) An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. A GaN-based light emitting diode element having a forward voltage of 5.5 V or less when a forward current applied to the light emitting diode element is 200 mA.
(5) An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. A GaN-based light emitting diode element having a forward voltage of 6.0 V or less when a forward current applied to the light emitting diode element is 350 mA.
(6) The light emitting diode structure includes an active layer made of a GaN-based semiconductor, an n-type GaN-based semiconductor layer disposed between the active layer and the m-plane GaN substrate, and the n-type GaN-based semiconductor layer. And a p-type GaN-based semiconductor layer sandwiching the active layer. The GaN-based light-emitting diode element according to any one of (1) to (5).
(7) The area of the back surface of the m-plane GaN substrate is 0.0012 cm ² or more (1)
The GaN-type light emitting diode element in any one of-(6).
(8) The GaN-based light emitting diode device according to (7), wherein an area of the n-side ohmic electrode is 0.0012 cm ² or more and not more than an area of the back surface of the m-plane GaN substrate.
(9) The back surface of the m-plane GaN substrate has an arithmetic average roughness Ra in a range of 10 μm square of 0.1 nm or less at least in a portion in contact with the n-side ohmic electrode. The semiconductor light-emitting device according to any one of the above.
(10) The GaN-based light emitting diode element according to any one of (1) to (9), wherein the n-side ohmic electrode is patterned.

According to one aspect of the present invention, the following GaN-based light emitting diode device is provided.
(11) An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. The forward voltage when the forward current applied to the light emitting diode element is 20 mA is 4 A GaN-based light emitting diode element having a voltage of 0.0 V or less.
(12) An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. And the n-side ohmic electrode formed on the flat portion of the rough processed portion, and the forward voltage when the forward current applied to the light emitting diode element is 60 mA is 4 A GaN-based light emitting diode element having a voltage of 5 V or less.
(13) An n-type conductive m-plane GaN substrate, a light-emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. And the n-side ohmic electrode formed on the flat portion of the rough processed portion, and the forward voltage when the forward current applied to the light emitting diode element is 120 mA is 5 A GaN-based light emitting diode element having a voltage of 0.0 V or less.
(14) An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. And the n-side ohmic electrode formed on the flat portion of the rough processed portion, and the forward voltage when the forward current applied to the light emitting diode element is 200 mA is 5 A GaN-based light emitting diode element having a voltage of 5 V or less.
(15) An n-type conductive m-plane GaN substrate, a light-emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a back surface of the m-plane GaN substrate. And the n-side ohmic electrode formed on the flat portion of the rough processed portion, and the forward voltage when the forward current applied to the light emitting diode element is 350 mA is 6 A GaN-based light emitting diode element having a voltage of 0.0 V or less.
(16) The GaN-based light-emitting diode element according to any one of (11) to (15), wherein the rough processed portion is a portion processed so as to form submicron-sized irregularities.

According to another aspect of the present invention, the following GaN-based light emitting diode device is provided.
(17) A substrate, which is an n-type conductive m-plane GaN substrate, an epi layer made of a GaN-based semiconductor epitaxially grown on the substrate and including a pn junction type light emitting structure, and an n-side formed on the back surface of the substrate An electrode, a translucent p-side ohmic electrode formed on the upper surface of the epi layer, and a p-side electrode pad formed on a part of the p-side ohmic electrode,
Of the back surface of the substrate, the region covered with the n-side electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry-etched region,
A GaN-based light emitting diode element, wherein all or part of the orthogonal projection of the p-side electrode pad on the back surface of the substrate is included in the high contact resistance region.
(18) An auxiliary electrode connected to the p-side electrode pad is formed on the p-side ohmic electrode, and all or a part of the orthogonal projection of the auxiliary electrode to the back surface of the substrate is the high contact resistance. The GaN-based light emitting diode device according to (17), which is not included in the region.
(19) A substrate which is an n-type conductive m-plane GaN substrate, an epi layer comprising a pn-junction light-emitting structure epitaxially grown on the substrate, and a light transmission formed on the back surface of the substrate An n-side ohmic electrode, an n-side electrode pad formed on a part of the n-side ohmic electrode, and a p-side electrode formed on the upper surface of the epi layer, The region covered with the n-side ohmic electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry etched region,
A GaN-based light emitting diode element, wherein all or part of an orthogonal projection of the n-side electrode pad on the back surface of the substrate is included in the high contact resistance region.
(20) An auxiliary electrode connected to the n-side electrode pad is formed on the n-side ohmic electrode, and all or a part of the orthogonal projection of the auxiliary electrode to the back surface of the substrate is the high contact resistance. The GaN-based light emitting diode device according to (19), which is not included in the region.
(21) A substrate which is an n-type conductive m-plane GaN substrate, an epitaxial layer made of a GaN-based semiconductor epitaxially grown on the substrate and including a pn junction type light emitting structure, and partially formed on the back surface of the substrate An n-side electrode and a p-side electrode formed on the upper surface of the epi layer,
The n-side electrode has a pad part and an auxiliary part connected to the pad part,
Of the back surface of the substrate, the region covered with the n-side electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry etched region,
A GaN-based light emitting diode element, wherein all or part of the orthogonal projection of the pad portion on the back surface of the substrate is included in the high contact resistance region.
(22) The GaN-based light-emitting diode element according to (21), wherein all or part of the orthogonal projection of the auxiliary portion on the back surface of the substrate is not included in the high contact resistance region.
(23) Said (19)-(22) whose carrier concentration of the said board | substrate is 10 ^{< 17} > cm ^<-3 >.
A GaN-based light emitting diode device according to any one of the above.

According to still another aspect of the present invention, the following method for manufacturing a GaN-based light emitting diode element is provided.
(24) (i) preparing an epi-wafer having a substrate which is an n-type conductive m-plane GaN substrate and an epi layer made of a GaN-based semiconductor epitaxially grown on the substrate and including a pn junction type light emitting structure One step,
(Ii) a second step of polishing the back surface of the substrate included in the epi-wafer;
(Iii) a third step of forming an n-side ohmic electrode over the entire back surface of the substrate polished in the second step;
(Iv) a fourth step of patterning the n-side ohmic electrode formed in the third step by etching;
The manufacturing method of the GaN-type light emitting diode element which has this.
(25) The manufacturing method according to (24), further including a fifth step of roughly processing the back surface of the substrate exposed in the fourth step.
(26) The manufacturing method according to (25), wherein in the fifth step, an uneven pattern having periodicity is formed on the back surface of the substrate exposed in the fourth step.
(27) The n-side ohmic electrode is a polycrystalline transparent conductive oxide film, and in the fourth step, a part of the n-side ohmic electrode is etched so that the residue remains on the substrate. In the fifth step, the exposed back surface of the substrate is roughly processed by dry etching using the residue as an etching mask.
(28) The manufacturing method according to (24), further including a sixth step of forming a reflective film on the back surface of the substrate exposed in the fourth step.
(29) The manufacturing method according to (28), wherein the reflective film is a dielectric reflective film.
(30) The manufacturing method according to any one of (24) to (29), wherein the back surface of the substrate to be polished in the second step is lapped immediately before the second step.
(31) The above-mentioned (24) to (30), wherein the carrier concentration of the substrate is 10 ¹⁷ cm ^−3.
The manufacturing method in any one of.

  Since the semiconductor light emitting element according to the above (1) to (16) according to the embodiment of the present invention has an n-side ohmic electrode formed on the back surface of the m-plane GaN substrate, solder is used on the metal electrode. Can be fixed. That is, it can be mounted in a form with good heat dissipation. Moreover, since the forward voltage is kept low, the amount of heat generation is small, and it is extremely suitable as an excitation light source for white LEDs.

  In the GaN-based light emitting diode device according to any one of (17) to (23) according to the embodiment of the present invention, by controlling a path of a current flowing in the device, at least one of the n-side electrode and the p-side electrode The shielding or absorption of light by the included electrode pad can be suppressed. Further, by controlling the path of the current flowing in the element and making the density of the current flowing in the light emitting structure uniform, it is possible to suppress a decrease in light emission efficiency due to the droop phenomenon.

  According to the GaN-based light-emitting diode element manufacturing method according to the above (24) to (31) according to the embodiment of the present invention, a GaN-based light source having a low contact resistance n-side electrode formed on the back surface of the m-plane GaN substrate. Light emitting diodes can be manufactured.

It is a schematic diagram which shows the structure of the GaN-type light emitting diode element which the present inventors made as an experiment, FIG. 1 (a) is a top view, FIG.1 (b) is a cross section in the position of the XX line of FIG. FIG. It is a top view of a mask pattern. It is a top view for demonstrating the direction of a mask pattern. It is a SEM image of the back surface of the m-plane GaN substrate which gave processing e. (Drawing substitute photo) It is drawing which shows typically the structure of the GaN light emitting diode element (Embodiment 1) which concerns on embodiment of this invention, Fig.5 (a) is the top view seen from the epi layer side, FIG.5 (b) is FIG. It is sectional drawing in the position of the XX line of (a). It is drawing which shows typically the structure of the GaN light emitting diode element (Embodiment 2) which concerns on embodiment of this invention, Fig.6 (a) is the top view seen from the epi layer side, FIG.6 (b) is FIG. It is sectional drawing in the position of the XX line of (a). It is drawing which shows typically the structure of the GaN light emitting diode element (Embodiment 3) based on embodiment of this invention, Fig.7 (a) is the top view seen from the epi layer side, FIG.7 (b) is FIG. It is sectional drawing in the position of the XX line of (a). It is drawing which shows typically the structure of the GaN light emitting diode element (Embodiment 4) based on embodiment of this invention, Fig.8 (a) is the top view seen from the board | substrate side, FIG.8 (b) is FIG. It is sectional drawing in the position of XX of a). It is drawing which shows typically the structure of the GaN light emitting diode element (Embodiment 5) which concerns on embodiment of this invention, Fig.9 (a) is the top view seen from the board | substrate side, FIG.9 (b) is FIG.9 ( It is sectional drawing in the position of XX of a). It is drawing which shows typically the structure of the GaN light emitting diode element (Embodiment 6) which concerns on embodiment of this invention, Fig.10 (a) is the top view seen from the board | substrate side, FIG.10 (b) is FIG. It is sectional drawing in the position of XX of a). FIG. 11 is a drawing schematically showing the structure of a GaN-based light emitting diode device (Embodiment 7) according to an embodiment of the present invention, FIG. 11A is a plan view seen from the epi layer side, and FIG. It is sectional drawing in the position of XX of 11 (a). It is the top view which looked at the GaN-type light emitting diode element shown in FIG. 11 from the substrate side. It is sectional drawing which shows typically the structure of the GaN-type light emitting diode element (Embodiment 8) which concerns on embodiment of this invention. FIGS. 14A and 4B are cross-sectional views schematically showing the structure of a GaN-based light emitting diode element (Embodiments 9 and 10) according to an embodiment of the present invention, respectively. FIGS. 15A and 15B are diagrams illustrating patterns exhibited by the n-side ohmic electrode on the back surface of the substrate, respectively. It is drawing which shows typically the structure of the GaN-type light emitting diode element (Embodiment 11) based on embodiment of this invention, Fig.16 (a) is the top view seen from the board | substrate side, FIG.16 (b) is FIG.16. It is sectional drawing in the position of the XX line of (a). It is drawing which shows typically the structure of the GaN-type light emitting diode element (Embodiment 12) based on embodiment of this invention, Fig.17 (a) is the top view seen from the board | substrate side, FIG.17 (b) is FIG.17. It is sectional drawing in the position of the PQ line of (a). It is drawing which shows typically the structure of the GaN-type light emitting diode element (Embodiment 13) based on embodiment of this invention, Fig.18 (a) is the top view seen from the board | substrate side, FIG.18 (b) is FIG.18. It is sectional drawing in the position of the PQ line of (a). It is drawing which shows typically the structure of the GaN-type light emitting diode element (Embodiment 14) based on embodiment of this invention, Fig.19 (a) is the top view seen from the board | substrate side, FIG.19 (b) is FIG.19. It is sectional drawing in the position of the XX line of (a). 20 is a drawing schematically showing the structure of a GaN-based light emitting diode element (Embodiment 15) according to an embodiment of the present invention, FIG. 20 (a) is a plan view seen from the substrate side, and FIG. 20 (b) is FIG. It is sectional drawing in the position of the PQ line of (a). It is process sectional drawing for demonstrating the manufacturing method which concerns on embodiment of this invention. It is process sectional drawing for demonstrating the manufacturing method which concerns on embodiment of this invention. It is process sectional drawing for demonstrating the manufacturing method which concerns on embodiment of this invention. It is process sectional drawing for demonstrating the manufacturing method which concerns on embodiment of this invention.

  The results of trial manufacture and evaluation of a GaN-based light emitting diode element (hereinafter also referred to as “LED element”) by the present inventors are described below.

1. Basic Structure of Prototype LED Element FIG. 1 schematically shows the basic structure of the prototype LED element. 1A is a top view, and FIG. 1B is a cross-sectional view taken along the line XX in FIG. 1A. As shown to Fig.1 (a), the planar shape of the LED element 1 is a rectangle, and a size is 350 micrometers x 340 micrometers.

As shown in FIG. 1B, the LED element 1 has a semiconductor stacked body 20 made of a GaN-based semiconductor on a substrate 10. The substrate 10 is an m-plane GaN substrate, and the semiconductor stacked body 20 is disposed on the front surface 11 of the substrate 10. The semiconductor stacked body 20 includes, in order from the substrate 10 side, a first undoped GaN layer 21, a Si-doped n-type GaN contact layer 22, a second undoped GaN layer 23, a Si-doped n-type GaN cladding layer 24, an MQW. It has an active layer 25, a Mg-doped p-type Al _0.1 Ga _0.9 N cladding layer 26, and an Mg-doped p-type Al _0.03 Ga _0.97 N contact layer 27.

The MQW active layer 25 has undoped In _0.04 Ga _0.96 N barrier layers and undoped In _0.16 Ga _0.84 N well layers that are alternately stacked. The number of undoped InGaN barrier layers is four, and the number of undoped InGaN well layers is three. Therefore, the lowermost layer and the uppermost layer of the MQW active layer 25 are both barrier layers. The composition of the well layer is adjusted so that the emission peak wavelength falls within the range of 445 to 465 nm.

  The LED element 1 has two n-side electrodes and one p-side electrode. One of the n-side electrodes is a first n-side metal pad E11, which is provided so as to cover the entire back surface 12 of the substrate 10. The other is the second n-side metal pad E12, which is formed on the surface of the n-type GaN contact layer 22 exposed by partially removing the semiconductor stacked body 20. Both the first n-side metal pad E11 and the second n-side metal pad E12 also serve as ohmic electrodes. The p-side electrode is composed of an ohmic translucent electrode E21 formed on the upper surface of the p-type AlGaN contact layer 27 and a p-side metal pad E22 formed on a part of the translucent electrode E21. It is. The current application to the MQW active layer 25 can be performed through the first n-side metal pad E11 and the p-side metal pad E22, or can be performed through the second n-side metal pad E12 and the p-side metal pad E22. .

  The first n-side metal pad E11 is a multilayer film, and includes a TiW layer, an Au layer, a Pt layer, an Au layer, a Pt layer, an Au layer, a Pt layer, and an Au layer in order from the substrate 10 side. The second n-side metal pad E12 is also a multilayer film having a similar laminated structure, and in order from the n-type GaN contact layer 22 side, a TiW layer, an Au layer, a Pt layer, an Au layer, a Pt layer, an Au layer, a Pt layer, It has an Au layer. The translucent electrode E21 is an ITO (indium tin oxide) film. The p-side metal pad E12 is a multilayer film having a laminated structure similar to that of the first n-side metal pad E11 and the second n-side metal pad E12, and sequentially includes a TiW layer, an Au layer, and Pt from the translucent electrode E21 side. A layer, an Au layer, a Pt layer, an Au layer, a Pt layer, and an Au layer.

2. Prototyping of LED Element An LED element 1 was produced by the following procedure.
2-1. Epitaxial growth Size is 7 mm (c-axis direction) x 15 mm (a-axis direction) x 330 μm (thickness), and the off-angle of the front surface (main surface on which the semiconductor laminate is provided) is 0 ± 0.5 ° The n-type conductive m-plane GaN substrate to which Si was added as an n-type impurity was prepared. The carrier concentration of the m-plane GaN substrate examined by hole measurement was 1.3 × 10 ¹⁷ cm ⁻³ .

A plurality of GaN-based semiconductor layers were epitaxially grown on the front surface of the m-plane GaN substrate using the atmospheric pressure MOVPE method to form a semiconductor laminate. TMG (trimethylgallium), TMI (trimethylindium) and TMA (trimethylaluminum) for Group III materials, ammonia for Group V materials, silane for Si materials, bisethylcyclopentadienylmagnesium ((EtCp) for Mg materials ) ₂ Mg) was used.

  Table 1 shows the growth temperature and film thickness of each layer.

  Table 2 shows the concentration of impurities added to the n-type GaN contact layer, n-type GaN clad layer, p-type AlGaN clad layer, and p-type AlGaN contact layer.

  The activation of Mg added to the p-type AlGaN cladding layer and the p-type AlGaN contact layer is performed while the p-type AlGaN contact layer is grown for a predetermined time and then the substrate temperature is lowered to room temperature in the growth furnace of the MOVPE apparatus. This was carried out using a method for controlling the flow rates of nitrogen gas and ammonia gas flowing into the growth furnace.

2-2. Formation of p-side electrode and second n-side metal pad An ITO film having a thickness of 210 nm was formed on the surface of the semiconductor laminate formed by the epitaxial growth (surface of the p-type AlGaN contact layer) by electron beam evaporation. Subsequently, the ITO film was patterned into a predetermined shape using photolithography and etching techniques to form a translucent electrode. After patterning, a part of the semiconductor stacked body is removed by reactive ion etching (RIE) processing to expose the n-type GaN contact layer at the site where the second n-side metal pad is to be formed, and perform mesa formation. It was. In RIE processing, Cl ₂ is used as an etching gas, the antenna / bias is 100 W / 20 W,
The pressure in the chamber was set to 0.3 Pa.

Subsequent to the RIE process, the produced ITO film was heat-treated at 520 ° C. for 20 minutes in the air atmosphere. Furthermore, using an RTA (Rapid Thermal Annealing) device,
This ITO film was heat-treated at 500 ° C. for 1 minute in a nitrogen gas atmosphere.

After the heat treatment of the ITO film, a second n-side metal pad and a p-side metal pad were simultaneously formed in a predetermined pattern using a lift-off method. All layers (TiW layer, Au layer, and Pt layer) included in the metal multilayer film constituting the second n-side metal pad and the p-side metal pad were formed by sputtering. When forming a TiW film, a Ti-W target having a Ti content of 10 wt% is used as a target, Ar (argon) is used as a sputtering gas, sputtering conditions are RF power 800 W, Ar flow rate 50 sccm, sputtering gas pressure 2.2. × 10 ⁻¹ Pa. The thickness of the lowermost TiW layer and the Au layer laminated immediately above it was 108 nm, and the thicknesses of the other Pt layers and Au layers were all 89 nm.

After forming the second n-side metal pad and p-side metal pad, a passivation film made of SiO ₂ was formed to a thickness of 213 nm on the exposed surface of the semiconductor stacked body and the surface of the translucent electrode.

2-3. Processing of the back surface of the m-plane GaN substrate After the formation of the passivation film, six different processes described below as processing a to processing f were performed on the back surface of the m-plane GaN substrate.

  Process a: The thickness of the substrate was reduced to 200 μm by lapping and polishing the back surface of the m-plane GaN substrate in this order.

  In the lapping process, the grain size of the diamond abrasive used was gradually reduced in accordance with a conventional method.

In the polishing step, a CMP slurry in which acid is added to acidic colloidal silica (particle size 70-100 nm) and the pH is adjusted to less than 2 is used, and the load is adjusted so that the polishing rate is 0.5 μm / h. The processing time was about 14 hours. The surface of the m-plane GaN substrate polished under these conditions has an arithmetic average roughness Ra in the range of 10 μm square measured using AFM (for example, DIMENSION 5000 manufactured by DIGITALINSTRUMENTS) of 0.1 nm or less.

  The polished surface (the back surface of the m-plane GaN substrate) is washed with water, further washed with IPA and acetone at room temperature, and then dried with ultraviolet ozone cleaning (110 ° C., oxygen flow rate 5 L / min) for 5 minutes. gave.

  Process b: After process a, the surface layer portion was further removed from the back surface of the m-plane GaN substrate by RIE. The RIE condition is the above 2-2. The etching time was set to 60 seconds so that the etching depth was 0.1 μm under the same conditions as when the RIE processing was performed on the semiconductor laminate. When the roughness of the surface after RIE processing was measured with a stylus type step gauge (ET3000 manufactured by Kosaka Laboratory Ltd.), the arithmetic average roughness Ra was 0.02 μm, and the maximum height Rz was 0.04 μm.

Processing c: After processing a, the surface layer portion was further scraped off from the back surface of the m-plane GaN substrate by RIE. The RIE condition is the above 2-2. The etching time is set to 610 so that the etching depth is 1.0 μm under the same conditions as when the RIE processing is performed on the semiconductor stacked body.
Set to seconds. When the surface roughness after RIE processing was measured with a stylus profilometer, the arithmetic average roughness Ra was 0.06 μm, and the maximum height Rz was 0.55 μm.

  Processing d: After processing a, the surface layer portion was further scraped off from the back surface of the m-plane GaN substrate by RIE. The RIE condition is the above 2-2. The etching time was set to 1220 seconds so that the etching conditions were the same as those when the RIE processing was performed on the semiconductor laminate. When the surface roughness after RIE processing was measured with a stylus profilometer, the arithmetic average roughness Ra was 0.07 to 0.12 μm, and the maximum height Rz was 1.30 μm.

  Process e: A positive photoresist (Sumiresist PFI-34AL manufactured by Sumitomo Chemical Co., Ltd.) using a novolac resin is coated on the back surface of the m-plane GaN substrate after the process a to a thickness of 1.6 μm. The mask pattern shown in FIG. 2 was formed by patterning the photoresist using a photolithography technique. That is, it is a mask pattern in which a plurality of circular etching masks are arranged at the lattice positions of a triangular lattice. The diameter of each circular mask (R in FIG. 2) was 2 μm, and the space between adjacent circular masks (S in FIG. 2) was 2.5 μm. As shown in FIG. 3, the direction of the mask pattern was determined so that the two sides BC and EF of the regular hexagon ABCDEF having the six lattice positions of the triangular lattice as vertices were orthogonal to the c-axis of the m-plane GaN substrate. .

The back surface of the m-plane GaN substrate was processed into a concavo-convex shape by performing RIE using the mask pattern formed as described above as an etching mask. Cl ₂ was used as an etching gas, the antenna / bias was set to 100 W / 20 W, the pressure in the chamber was set to 0.3 Pa, and the etching selectivity was about 1. The etching selectivity here is [GaN etching rate] / [mask etching rate] when the etching time is about 800 seconds or less. Under these conditions, RIE processing was performed for 1500 seconds. The mask pattern almost disappeared when the etching time reached about 800 seconds. After the RIE processing, the wafer was cleaned using an organic solvent, and then the surface subjected to the RIE processing was subjected to ultraviolet ozone cleaning (110 ° C., oxygen flow rate 5 L / min) for 5 minutes.

  FIG. 4 shows an SEM image of the back surface of the m-plane GaN substrate subjected to the processing e. 4A is a plan view, FIG. 4B is a diagram viewed from the cross-sectional direction, and FIG. 4C is a perspective view. 4A to 4C, the direction from right to left in the drawing is the [0001] direction (c + direction) of GaN, and the direction from left to right is [000-1] of GaN. ] Direction (c-direction). The height of the protrusion formed on the back surface of the m-plane GaN substrate was 1.5 μm.

  Process f: A mask pattern was formed on the back surface of the m-plane GaN substrate after process a by the same procedure as process e. However, after being installed in the RIE chamber, the back surface of the m-plane GaN substrate was covered with a thin sapphire plate to protect the back surface from being subjected to RIE processing. Except for this, the process performed in process f is the same as process e. That is, on the back surface of the m-plane GaN substrate subjected to processing f, a process of forming a mask pattern using a photoresist, a process of removing the mask pattern using an organic solvent, and an ultraviolet ozone after removing the mask pattern A cleaning process is being performed.

2-4. Formation of first n-side metal pad A metal multilayer film serving as a first n-side metal pad was formed on the back surface of the m-plane GaN substrate subjected to any of the above processes a to f. All layers (TiW layer, Au layer, and Pt layer) included in this metal multilayer film were formed by sputtering. When forming a TiW film, a Ti-W target having a Ti content of 10 wt% is used as a target, Ar (argon) is used as a sputtering gas, sputtering conditions are RF power 800 W, Ar flow rate 50 sccm, sputtering gas pressure 2.2. × 10 ⁻¹ Pa. The thickness of the lowermost TiW layer and the Au layer stacked immediately above it is 1
The thickness of the other Pt layer and Au layer was 89 nm.

  After the metal multilayer film was formed, the wafer was divided by scribing and breaking to form LED elements as chips. The metal multilayer film was cut together with the GaN substrate in this step. Therefore, the planar shape of the first n-side metal pad is the same as the shape of the back surface of the m-plane GaN substrate. The size of the first n-side metal pad was 350 μm × 340 μm, which was substantially the same as the chip size.

2-5. Evaluation of forward voltage Forward voltage (Vf ₁ ) when current is applied through the first n-side metal pad and p-side metal pad to the LED chip obtained by the above procedure, and the second n-side The forward voltage (Vf ₂ ) when current was applied through the metal pad and the p-side metal pad was compared. The applied current was a pulse current having a pulse width of 1 msec and a pulse period of 100 msec, and the current value was 20 mA and 60 mA. The results are shown in Table 3.

As shown in Table 3, Vf ₁ and Vf ₂ coincided with the LED chip in which only the processing a was performed on the back surface of the m-plane GaN substrate, whereas Vf ₁ was all in the LED chips subjected to processing b to f. It becomes larger than the vf _2. In particular, the difference between the LED chips subjected to processing b to e including RIE processing was several V or more.

Further, Vf ₁ when forward current of 20 mA, 60 mA, 100 mA, 120 mA, 180 mA, 240 mA, and 350 mA is applied to an LED chip that has been processed only on the back surface of the m-plane GaN substrate with a pulse width of 1 msec and a pulse period of 100 msec. Is shown in Table 4. Table 4 also shows the average current density in the first n-side metal pad in each case. This average current density is a value obtained by dividing the forward current by the area of the n-side metal pad (350 μm × 340 μm), and is an average of the current flowing across the interface between the n-side metal pad and the back surface of the m-plane GaN substrate. Represents density.

From the above results, it is considered that the following semiconductor light emitting devices (I) to (XI) can be realized.
(I) An n-type conductive m-plane GaN substrate, a light emitting structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and formed on the back surface of the m-plane GaN substrate A semiconductor light emitting device having an n-side ohmic electrode and having a forward voltage of 4.0 V or less when a forward current applied to the device is 20 mA.
(II) an n-type conductive m-plane GaN substrate, a light emitting structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and formed on the back surface of the m-plane GaN substrate A semiconductor light emitting device having an n-side ohmic electrode and having a forward voltage of 4.5 V or less when a forward current applied to the device is 60 mA.
(III) An n-type conductive m-plane GaN substrate, a light emitting structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and formed on the back surface of the m-plane GaN substrate A semiconductor light emitting device having an n-side ohmic electrode and having a forward voltage of 5.0 V or less when a forward current applied to the device is 120 mA.
(IV) An n-type conductive m-plane GaN substrate, a light emitting structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and formed on the back surface of the m-plane GaN substrate A semiconductor light emitting device having an n-side ohmic electrode and having a forward voltage of 5.5 V or less when a forward current applied to the device is 200 mA.
(V) an n-type conductive m-plane GaN substrate, a light emitting structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and formed on the back surface of the m-plane GaN substrate A semiconductor light emitting device having an n-side ohmic electrode and having a forward voltage of 6.0 V or less when a forward current applied to the device is 350 mA.
(VI) The light emitting structure includes an active layer made of a GaN-based semiconductor, an n-type GaN-based semiconductor layer disposed between the active layer and the m-plane GaN substrate, and the n-type GaN-based semiconductor layer. A semiconductor light emitting device according to any one of (I) to (V), comprising a p-type GaN-based semiconductor layer sandwiching the active layer.
(VII) The semiconductor light-emitting device according to any one of (I) to (VI), which is a light-emitting diode device.
(VIII) The semiconductor light-emitting device according to any one of (I) to (VII), wherein an area of the back surface of the m-plane GaN substrate is 0.0012 cm ² or more.
(IX) The semiconductor light emitting element according to (VII), wherein an area of the n-side ohmic electrode is 0.0012 cm ² or more and not more than an area of the back surface of the m-plane GaN substrate.
(X) The semiconductor light-emitting device according to any one of (I) to (IX), wherein the carrier concentration of the m-plane GaN substrate is 1 × 10 ¹⁷ cm ⁻³ .
(XI) The back surface of the m-plane GaN substrate has an arithmetic average roughness Ra in a range of 10 μm square of 0.1 nm or less in at least a portion in contact with the n-side ohmic electrode. The semiconductor light-emitting device according to any one of the above.

The present invention has been completed based on the knowledge obtained from the trial manufacture and evaluation of the LED elements described above. However, it goes without saying that the present invention is not limited to a prototype LED element or a method used in the trial production.

  Below, the manufacturing method of the GaN-type light emitting diode element which concerns on embodiment of this invention, and a GaN-type light emitting diode element is demonstrated.

(Embodiment 1)
The structure of the GaN-based light emitting diode element according to Embodiment 1 is schematically shown in FIG. The GaN-based light emitting diode element 100 includes a substrate 110 and an epi layer 120 made of a GaN-based semiconductor epitaxially grown thereon. FIG. 5A is a plan view of the GaN-based light emitting diode element 100 as viewed from the epi layer 120 side, and FIG. 5B is a cross-sectional view taken along the line XX in FIG.

  The substrate 110 is an n-type conductive m-plane GaN substrate. The epi layer 120 includes an n-type layer 121 and a p-type layer 123 that form a pn junction. An active layer 122 is provided between the n-type layer 121 and the p-type layer 123 so that a double heterostructure is formed. An n-side electrode E100 that serves both as an ohmic electrode and an electrode pad is provided on the back surface of the substrate 110, and a p-side ohmic electrode E201 that is a translucent electrode is provided on the epi layer 120. Light emission occurs in the active layer 122 by applying a forward voltage to the epi layer 120 through the n-side electrode E100 and the p-side electrode pad E202 formed in part on the p-side ohmic electrode E201. This light passes through the p-side ohmic electrode E201 and is emitted to the outside of the GaN-based light emitting diode element. A part of this light is also emitted from the end face of the substrate 110 and the end face of the epi layer 120.

  The n-side electrode E100 preferably has a laminated structure. In that case, the portion in contact with the substrate 110 is formed using a material that forms ohmic contact with an n-type GaN-based semiconductor, such as Al, Ti, Cr, V, W, ITO, and the other portions are Au, Al, It is formed using a highly conductive metal such as Cu or Ag.

  The p-side ohmic electrode E201 is formed using a transparent conductive oxide (TCO) such as ITO. The p-side ohmic electrode E201 is preferably formed so as to cover the entire upper surface of the p-type layer 123. The p-side electrode pad E202 is formed using a metal, and preferably has a laminated structure. When the p-side electrode pad E202 has a laminated structure, the portion in contact with the p-side ohmic electrode E201 is formed of a metal having excellent adhesion to TCO, such as Cr, Ti, Ni, Pt, and Rh, and other portions. Is formed using a highly conductive metal such as Au, Al, Cu, or Ag. The thickness of the p-side ohmic electrode E201 formed of TCO is preferably 0.1 μm to 0.5 μm, and the thickness of the p-side electrode pad E202 formed of metal is preferably 0.5 μm to 5 μm.

  The n-side electrode E100 covers the entire back surface of the substrate 110. On the back surface of the substrate 110, there are a low contact resistance region 112a having a relatively low contact resistance with the n-side electrode E100 and a high contact resistance region 112b having a relatively high contact resistance. The low contact resistance region 112a is polished. That is, the last process (not including cleaning) performed on the low contact resistance region 112a before forming the n-side electrode E100 is a polishing process. On the other hand, the high contact resistance region 112b is dry-etched. That is, the last process performed on the high contact resistance region 112b before forming the n-side electrode E100 is a dry etching process such as reactive ion etching (RIE).

As proved from the LED device prototype and evaluation results described above, by polishing an n-type conductive m-plane GaN substrate with an acidic CMP slurry at a polishing rate as low as 0.5 μm / h or less. An electrode having a low contact resistance can be formed on the obtained surface (m-plane). On the other hand, an electrode formed on the surface of an m-plane GaN substrate that has been further subjected to dry etching after polishing exhibits higher contact resistance.

  The high contact resistance region 112b only needs to include at least a part of the orthogonal projection of the p-side electrode pad E202 on the back surface of the substrate 110, but is preferably formed to include all. With this configuration, the current flowing in the substrate 110 and the epi layer 120 is concentrated on the path connecting the p-side electrode pad E202 and the n-side electrode E100 with the shortest distance (the path indicated by the arrow in FIG. 5B). It is prevented. As a result, the shielding and absorption received by the p-side electrode pad E202 by the light generated in the active layer 122 is reduced as compared with the case where current is concentrated in this region. In addition, since the density of the current flowing across the active layer 122 becomes more uniform, the light emission efficiency decreases due to the droop phenomenon (a phenomenon that the light emission efficiency decreases as the current density increases, which is peculiar to the GaN-based light emitting diode element). It is suppressed.

(Embodiment 2)
The structure of a GaN-based light emitting diode element according to Embodiment 2 is schematically shown in FIG. In FIG. 6, the same reference numerals are given to components common to the GaN-based light emitting diode element of the first embodiment. FIG. 6A is a plan view of the GaN-based light emitting diode device 100 as viewed from the epi layer 120 side, and FIG. 6B is a cross-sectional view taken along the line XX in FIG.

  In the GaN-based light emitting diode element 100 shown in FIG. 6, four auxiliary electrodes E203 are connected to the p-side electrode pad E202. Therefore, the current supplied from the metal wire or the like to the p-side electrode pad E202 is expanded in the lateral direction (direction perpendicular to the thickness direction of the epi layer 120) by the line-shaped auxiliary electrode E203, and then the p-side ohmic electrode. It will flow to E201.

  In the region covered with the n-side electrode E100 on the back surface of the substrate 110, the high contact resistance region 112b is formed so as to include at least part, preferably all, of the orthogonal projection of the p-side electrode pad E202. Therefore, it is possible to prevent the current flowing in the substrate 110 and the epi layer 120 from being concentrated on the path connecting the p-side electrode pad E202 and the n-side electrode E100 with the shortest distance. Further, since the auxiliary electrode E203 is connected to the p-side electrode pad E202, the current flowing in the epi layer 120 is spread to a region sufficiently separated from the p-side electrode pad E202 in the lateral direction.

  In the GaN-based light emitting diode device 100 of FIG. 6, the orthogonal projection of the auxiliary electrode E203 on the back surface of the substrate 110 is not included in the high contact resistance region 112b. Therefore, current flows in the direction immediately below from the auxiliary electrode E203, but the auxiliary electrode E203 is formed to be elongated unlike the p-side electrode pad E202, so the influence (shielding and absorption) on light emission that occurs immediately below the auxiliary electrode E203 is compared. Small. In one embodiment, the high contact resistance region 112b may be formed so as to include all or part of the orthogonal projection of the auxiliary electrode E203 onto the back surface of the substrate 110.

(Embodiment 3)
The structure of a GaN-based light emitting diode element according to Embodiment 3 is schematically shown in FIG. In FIG. 7, the same reference numerals are given to components common to the GaN-based light emitting diode element of the first embodiment. FIG. 7A is a plan view of the GaN-based light emitting diode device 100 as viewed from the epi layer 120 side, and FIG. 7B is a cross-sectional view taken along the line XX in FIG.

In the GaN-based light emitting diode element 100 shown in FIG. 7, an insulating film Z100 is formed between the epi layer 120 and the p-side ohmic electrode E201 at a position directly below the p-side pad electrode E100. By providing the two current block structures of the high contact resistance region 112b and the insulating film Z100 provided on the back surface of the substrate 110, the current flowing through the substrate 110 and the epi layer 120 is supplied to the p-side electrode pad E202 and the n-side electrode. Concentrating on the route connecting E100 with the shortest distance is effectively prevented.

(Embodiment 4)
The structure of a GaN-based light emitting diode element according to Embodiment 4 is schematically shown in FIG. In FIG. 8, the same reference numerals are given to components common to the GaN-based light emitting diode element of the first embodiment. FIG. 8A is a plan view of the GaN-based light emitting diode element 100 as viewed from the substrate 110 side, and FIG. 8B is a cross-sectional view taken along the line XX in FIG.

  In the GaN-based light emitting diode device 100 shown in FIG. 8, an n-side ohmic electrode E101 that is a translucent electrode is provided on the back surface of the substrate 110, and a p-side electrode E200 that serves both as an ohmic electrode and an electrode pad is provided on the epi layer 120. Is provided. By applying a forward voltage to the epi layer 120 through the n-side electrode pad E102 formed on a part of the n-side ohmic electrode E101 and the p-side electrode E200, the active layer 122 emits light. This light passes through the n-side ohmic electrode E101 and is emitted to the outside of the GaN-based light emitting diode element. A part of this light is also emitted from the end face of the substrate 110 and the end face of the epi layer 120.

  The n-side ohmic electrode E101 is formed using a transparent conductive oxide (TCO) such as ITO. The n-side electrode pad E102 is formed using a metal, and preferably has a laminated structure. When the n-side electrode pad E102 has a laminated structure, the portion in contact with the n-side ohmic electrode E201 is formed of a metal having excellent adhesion to TCO, such as Cr, Ti, Ni, Pt, and Rh, and other portions. Is formed using a highly conductive metal such as Au, Al, Cu, or Ag. The thickness of the n-side ohmic electrode E101 formed of TCO is preferably 0.1 μm to 0.5 μm, and the thickness of the n-side electrode pad E102 formed of metal is preferably 0.5 μm to 5 μm.

  The p-side electrode E200 is preferably a laminated structure. In that case, the portion that contacts the p-type layer 123 is formed using a material that forms ohmic contact with the p-type GaN-based semiconductor, such as Ni, Au, Pt, Pd, Co, and ITO, and the other portion is Au. , Al, Cu, and Ag are used to form a highly conductive metal. The p-side electrode E200 is preferably formed so as to cover the entire top surface of the p-type layer 123.

  The n-side ohmic electrode E101 covers the entire back surface of the substrate 110. On the back surface of the substrate 110, there are a low contact resistance region 112a having a relatively low contact resistance with the n-side ohmic electrode E101 and a high contact resistance region 112b having a relatively high contact resistance. The low contact resistance region 112a is a polished region, and the high contact resistance region 112b is a dry etched region.

  The high contact resistance region 112b is provided immediately below the n-side electrode pad E102. The high contact resistance region 112b only needs to include at least a part of the orthogonal projection of the n-side electrode pad E102 onto the back surface of the substrate 110, but is preferably formed to include all. With this configuration, the current flowing in the substrate 110 and the epi layer 120 is concentrated on the path connecting the p-side electrode E200 and the n-side electrode pad E102 with the shortest distance (the path indicated by the arrow in FIG. 8B). It is prevented. As a result, the shielding and absorption received by the n-side electrode pad E102 by the light generated in the active layer 122 is reduced as compared with the case where current is concentrated in this region. In addition, since the density of the current flowing across the active layer 122 becomes more uniform, the light emission efficiency decreases due to the droop phenomenon (a phenomenon that the light emission efficiency decreases as the current density increases, which is peculiar to the GaN-based light emitting diode element). It is suppressed.

(Embodiment 5)
The structure of a GaN-based light emitting diode element according to Embodiment 5 is schematically shown in FIG. In FIG. 9, the same reference numerals are given to components common to the GaN-based light emitting diode element of the first embodiment. FIG. 9A is a plan view of the GaN-based light emitting diode element 100 as viewed from the substrate 110 side, and FIG. 9B is a cross-sectional view taken along the line XX in FIG.

  In the GaN-based light emitting diode element 100 shown in FIG. 9, four auxiliary electrodes E103 are connected to the n-side electrode pad E102. Therefore, the current supplied from the metal wire or the like to the n-side electrode pad E102 is expanded in the lateral direction (direction orthogonal to the thickness direction of the substrate layer 110) by the line-shaped auxiliary electrode E103, and then the n-side ohmic electrode. It will flow to E101.

  In the region covered with the n-side ohmic electrode E101 on the back surface of the substrate 110, the high contact resistance region 112b is formed so as to include at least a part, preferably all, of the orthogonal projection of the n-side electrode pad E102. . Therefore, it is possible to prevent the current flowing through the substrate 110 and the epi layer 120 from being concentrated on the path connecting the p-side electrode E200 and the n-side electrode pad E102 with the shortest distance. Further, since the auxiliary electrode E103 is connected to the n-side electrode pad E102, the current flowing in the epi layer 120 is spread to a region sufficiently separated from the n-side electrode pad E102 in the lateral direction.

  In the GaN-based light emitting diode device 100 of FIG. 9, the orthogonal projection of the auxiliary electrode E103 onto the back surface of the substrate 110 is not included in the high contact resistance region 112b. Therefore, current flows also in the direction immediately below from the auxiliary electrode E103, but the auxiliary electrode E103 is formed in an elongated shape unlike the n-side electrode pad E202, so the influence (shielding and absorption) on the light emission that occurs immediately below is compared. Small. In one embodiment, the high contact resistance region 112b may be formed so as to include all or a part of the orthogonal projection of the auxiliary electrode E103 onto the back surface of the substrate 110.

(Embodiment 6)
The structure of the GaN-based light emitting diode element according to Embodiment 6 is schematically shown in FIG. In FIG. 10, the same reference numerals are given to components common to the GaN-based light emitting diode element of the first embodiment. FIG. 10A is a plan view of the GaN-based light emitting diode element 100 as viewed from the substrate 110 side, and FIG. 10B is a cross-sectional view taken along the line XX in FIG.

  In the GaN-based light emitting diode element 100 shown in FIG. 10, an n-side electrode E100 including a pad portion is directly formed on the back surface of the substrate 110. The n-side electrode E100 includes a pad portion E100a that also serves as an electrode pad, and an auxiliary portion E100b that is connected to the pad portion E100a and presents a cross pattern (also referred to as a branched linear pattern).

  The n-side electrode E100 is preferably formed by using a material that forms ohmic contact with an n-type GaN-based semiconductor, such as Al, Ti, Cr, V, W, ITO, etc. The portion is formed using a highly conductive metal such as Au, Al, Cu, or Ag.

In the region covered with the n-side electrode E100 in the back surface of the substrate 110, the high contact resistance region 112b is formed so as to include at least part, preferably all, of the orthogonal projection of the pad portion E100a of the n-side electrode. Yes. Accordingly, carriers (electrons) injected from the n-side electrode E100 into the substrate 110 are not directly from the pad portion E100a but are expanded in the lateral direction by the auxiliary portion E100b and then injected into the substrate 110. Therefore, the density of the current flowing through the light emitting structure in the epi layer 120 becomes uniform as compared with the case where the high contact resistance region 112b is not provided. Note that a current also flows from the auxiliary portion E100b in the direction immediately below, but the auxiliary portion E100b has a pad portion E10.
Since it is formed in an elongated shape unlike 0a, the influence (shielding and absorption) on the light emission that occurs immediately below it is small.

(Embodiment 7)
The structure of a GaN-based light emitting diode element according to Embodiment 7 is schematically shown in FIG. A GaN-based light emitting diode element 101 shown in FIG. 11 includes a substrate 110 and an epi layer 120 made of a GaN-based semiconductor epitaxially grown thereon. FIG. 11A is a plan view of the GaN-based light emitting diode element 101 as viewed from the epi layer 120 side, and FIG. 11B is a cross-sectional view taken along the line XX in FIG. FIG. 12 is a plan view of the GaN-based light emitting diode element 101 as viewed from the substrate 110 side.

  The substrate 110 is an n-type conductive m-plane GaN substrate. The epi layer 120 includes an n-type layer 121 and a p-type layer 123 that form a pn junction. An active layer 122 is provided between the n-type layer 121 and the p-type layer 123 so that a double heterostructure is formed. An n-side electrode E100 that serves both as an ohmic electrode and an electrode pad is formed on the back surface of the substrate 110. On the epi layer 120, a p-side ohmic electrode E201 which is a translucent electrode is formed. Light emission occurs in the active layer 122 by applying a forward voltage to the epi layer 120 through the n-side electrode E100 and the p-side electrode pad E202 formed in part on the p-side ohmic electrode E201. This light is emitted to the outside of the GaN-based light emitting diode element 101 from the surface of the p-side ohmic electrode E201, the end face of the epi layer 120, the end face of the substrate 110, and the like.

  The n-side electrode E100 is formed of a material that forms an ohmic contact with an n-type GaN-based semiconductor, such as Al, Ti, Cr, V, W, or ITO, at least at a portion in contact with the substrate 110. In a preferred embodiment, the n-side electrode E100 is formed of Al, Ti, Cr, V, W, ITO, or the like in contact with the substrate 110, and further has a conductive property such as Au, Al, Cu, or Ag. A multi-layer structure in which layers made of a high metal are laminated.

The p-side ohmic electrode E201 is formed of a transparent conductive oxide (TCO; Transparent Conductive Oxide) such as ITO. Preferably, the p-side ohmic electrode E201 is p
It is provided so as to cover the entire top surface of the mold layer 123. The p-side electrode pad E202 is formed using metal. In a preferred embodiment, the p-side electrode pad E202 is formed of a metal having excellent adhesion to TCO, such as Cr, Ti, Ni, Pt, and Rh, in contact with the p-side ohmic electrode E201. A multilayer structure in which layers made of highly conductive metals such as Au, Al, Cu, and Ag are stacked. The thickness of the p-side ohmic electrode E201 made of TCO is preferably 0.1 μm to 0.5 μm, and the thickness of the p-side electrode pad E202 made of metal is preferably 0.5 μm to 5 μm.

  As shown in FIG. 12, the n-side electrode E100 formed on the back surface of the substrate 110 is patterned into a specific shape. At the center of the n-side electrode E100, a circular opening is provided at a position overlapping the orthogonal projection of the p-side electrode pad E202 on the back surface of the substrate 110. Due to this opening, the current flowing from the p-side electrode pad E202 to the epi layer 120 does not concentrate directly below the p-side electrode pad E202. That is, the current does not concentrate on the path indicated by the arrow in FIG. As a result, the shielding and absorption received by the p-side electrode pad E202 by the light generated in the active layer 122 is reduced as compared with the case where current is concentrated in this path. In addition, since the density of the current flowing across the active layer 122 becomes more uniform, the light emission efficiency decreases due to the droop phenomenon (a phenomenon that the light emission efficiency decreases as the current density increases, which is peculiar to the GaN-based light emitting diode element). It is suppressed.

(Embodiment 8)
FIG. 13 schematically shows a cross-sectional structure of a GaN-based light emitting diode element according to the eighth embodiment. In FIG. 13, the same reference numerals are given to components common to the GaN-based light emitting diode element 101 of the seventh embodiment. In the GaN-based light emitting diode element 102 shown in FIG. 13, a concavo-convex pattern capable of irregularly reflecting light generated in the active layer 122 is provided in a portion of the back surface of the substrate 110 that is not covered with the n-side electrode E100. This concavo-convex pattern is, for example, a pattern in which dot-shaped concave portions or convex portions are periodically arranged, and can be formed by photolithography and dry etching. The concave / convex pattern can diffusely reflect light in the near ultraviolet to visible wavelength generated in the active layer 122 if the depth of the concave portion or the height of the convex portion and the pattern period are 1 μm or more. Multiple reflections are suppressed by forming a concavo-convex pattern that can cause irregular reflection, and the light extraction efficiency is improved. Instead of forming the concavo-convex pattern having periodicity, a rough surface having no periodicity can be formed by dry etching or sand blasting using a random etching mask.

(Embodiments 9 and 10)
FIG. 14 schematically shows a cross-sectional structure of a GaN-based light emitting diode element according to the ninth and tenth embodiments. In FIG. 14, the same reference numerals are given to components common to the GaN-based light emitting diode element 101 of the seventh embodiment. In the GaN-based light-emitting diode element 103 shown in FIG. 14A and the GaN-based light-emitting diode element 104 shown in FIG. 14B, a patterned n-side is used instead of the n-side electrode E100 that serves both as an ohmic electrode and an electrode pad. An ohmic electrode E101 and an n-side electrode pad E102 covering the ohmic electrode E101 are formed on the back surface of the substrate 110. The pattern exhibited by the n-side ohmic electrode E101 on the back surface of the substrate 110 can be a dot pattern shown as an example in FIG. 15A or a net pattern shown as an example in FIG. The n-side ohmic electrode E101 is preferably patterned by a subtractive method.

  In the GaN-based light emitting diode element 103 of FIG. 14A, the n-side electrode pad E102 is provided in contact with the exposed back surface of the substrate 110, but in the GaN-based light emitting diode element 104 of FIG. A dielectric reflection film R100 is interposed between the back surface of the substrate 110 and the n-side electrode pad E102. A suitable example of the dielectric reflection film R is a Bragg reflection film (DBR), but is not limited, and may be a single layer film made of a dielectric having a refractive index lower than that of the substrate 110.

  In the GaN-based light emitting diode elements 103 and 104, the n-side ohmic electrode E101 is vapor-deposited using a material that forms an ohmic contact with an n-type GaN-based semiconductor, such as Al, Ti, Cr, V, W, or ITO. It is preferably formed to a thickness of 0.05 μm to 0.5 μm by a vapor phase method such as sputtering or CVD. The n-side electrode pad E102 preferably includes a layer having a thickness of 0.5 μm to 5 μm made of a highly conductive metal such as Au, Al, Cu, or Ag. The n-side electrode pad E102 preferably includes a high reflection portion made of a metal having high reflectivity in the near ultraviolet to visible wavelength region, such as Ag, Al, Rh, and Pt, on the substrate 110 side.

(Embodiment 11)
The structure of the GaN-based light emitting diode element according to Embodiment 11 is schematically shown in FIG. 16A is a plan view seen from the substrate side, and FIG. 16B is a cross-sectional view taken along the line XX of FIG. In FIG. 16, the same reference numerals are given to components common to the GaN-based light emitting diode element 101 of the seventh embodiment. In the GaN-based light emitting diode element 105 shown in FIG. 16, the electrode provided on the p-type layer 123 is a p-side electrode E200 that serves both as an ohmic electrode and an electrode pad, and light generated in the active layer 122 is emitted from the substrate 110. The area of the n-side electrode E100 is reduced so as to be emitted from the back surface to the outside of the GaN-based light emitting diode element 100. In a preferred embodiment, the p-side electrode E200 is formed of a material that forms an ohmic contact with the p-type GaN-based semiconductor at a portion in contact with the p-type layer 123, and Au, Al, Cu, Ag, or the like is formed thereon. A multi-layer structure in which layers made of highly conductive metals are stacked. Examples of the material that forms ohmic contact with the p-type GaN-based semiconductor include metals such as Ni, Au, Pd, Rh, Pt, Co, ITO, zinc-doped indium oxide, zinc oxide, tin oxide, titanium oxide, Examples thereof include transparent conductive oxides such as gallium oxide. The layer made of a highly conductive metal is preferably formed to a thickness of 0.5 μm to 5 μm.

Embodiment 12
The structure of a GaN-based light emitting diode element according to Embodiment 12 is schematically shown in FIG. In FIG. 17, the same reference numerals are given to components common to the GaN-based light emitting diode element 101 of the seventh embodiment. A GaN-based light-emitting diode element 106 shown in FIG. 17 is a modification of the GaN-based light-emitting diode element 105 shown in FIG. As a difference, as shown in FIG. 17A, which is a plan view, in the GaN-based light emitting diode element 106, the n-side electrode E100 is electrically connected to the connecting portion E100a, which is a portion to which a bonding wire or the like is connected, in the lateral direction. It is comprised from the extension part E100b for expanding to (the direction orthogonal to the thickness direction of the board | substrate 110). In addition, in the GaN-based light emitting diode element 106, as shown in FIG. 17B, which is a cross-sectional view at the position of the PQ line in FIG. 17A, the exposed portion of the back surface of the substrate 110 is roughly processed. ing. In the rough processed portion, micron-sized irregularities that can diffusely reflect the light generated in the active layer 122, submicron-sized periodic irregularities pattern that can diffract the light generated in the active layer 122, or the active layer 122 Sub-micron-sized fine irregularities that can suppress the total reflection of light are formed. The submicron-sized unevenness can be formed by a method of etching the substrate 110 using polymer fine particles or silica fine particles as a mask.

(Embodiment 13)
The structure of a GaN-based light emitting diode element according to Embodiment 12 is schematically shown in FIG. 18A is a plan view seen from the substrate side, and FIG. 18B is a cross-sectional view taken along the line PQ in FIG. 18A. In FIG. 18, the same reference numerals are given to components common to the GaN-based light emitting diode element 101 of the seventh embodiment. A GaN-based light-emitting diode element 107 shown in FIG. 18 is another modification of the GaN-based light-emitting diode element 105 shown in FIG. As a difference, as shown in FIGS. 18A and 18B, in the GaN-based light emitting diode element 107, a transparent conductive oxide such as ITO is used instead of the n-side electrode E100 which serves both as an ohmic electrode and an electrode pad. A translucent n-side ohmic electrode E101 formed in (1) and an n-side electrode pad E102 provided on a part thereof are formed on the back surface of the substrate 110.

  Similarly to the n-side electrode E100 in the GaN-based light emitting diode element 106 of FIG. 17, the n-side electrode pad E102 has a connection portion E102a that is a portion to which a bonding wire or the like is connected, and an extension portion for spreading the current in the lateral direction. E102b. The translucent n-side ohmic electrode E101 is patterned and has a circular opening at a portion immediately below the n-side electrode pad E102a.

(Embodiment 14)
The structure of a GaN-based light emitting diode element according to Embodiment 14 is schematically shown in FIG. FIG. 19A is a plan view seen from the substrate side, and FIG. 19B is a cross-sectional view taken along the line XX of FIG. 19A. In FIG. 19, the same reference numerals are given to components common to the GaN-based light emitting diode element 101 of the seventh embodiment. A GaN-based light emitting diode element 108 shown in FIG. 19 is yet another modification of the GaN-based light emitting diode element 105 shown in FIG. As a difference, as shown in FIGS. 19A and 19B, the light-emitting diode 108 is formed of a transparent conductive oxide such as ITO instead of the n-side electrode E100 that serves both as an ohmic electrode and an electrode pad. The translucent n-side ohmic electrode E101 and the n-side electrode pad E102 provided on a part thereof are formed on the back surface of the substrate 110. However, GaN in FIG.
Unlike the system light emitting diode element 107, the n-side ohmic electrode E101 does not cover the back surface of the substrate 110 widely, and its area is only slightly larger than the n-side electrode pad E102. In addition, in the GaN-based light emitting diode element 108, unlike the GaN-based light emitting diode element 105 in FIG. 16, the portion of the back surface of the substrate 110 that is not covered with the n-side ohmic electrode E101 is a rough surface.

(Embodiment 15)
The structure of a GaN-based light emitting diode element according to Embodiment 15 is schematically shown in FIG. 20A is a plan view seen from the substrate side, and FIG. 20B is a cross-sectional view taken along the line PQ in FIG. 20A. In FIG. 20, the same reference numerals are given to components common to the GaN-based light emitting diode element 101 of the seventh embodiment. A GaN-based light emitting diode element 109 shown in FIG. 20 is a modification of the GaN-based light emitting diode element 108 shown in FIG. As a difference, in the GaN-based light emitting diode element 109, as shown in FIGS. 20 (a) and 20 (b), the n-side electrode pad E102 is electrically connected to the connecting portion E102a, which is a portion to which a bonding wire or the like is connected, in the lateral direction. It is comprised from the grid-like extension part E102b for expanding to (the direction orthogonal to the thickness direction of the board | substrate 110). The n-side ohmic electrode E101 interposed between the n-side electrode pad E102 and the p-type layer 123 has substantially the same shape as the n-side electrode pad E102, but is patterned a little wider.

(Method for Manufacturing GaN-Based Light Emitting Diode Device of Embodiment 7)
Next, a method for manufacturing a GaN-based light-emitting diode element according to an embodiment of the present invention will be described by taking as an example the case of manufacturing the GaN-based light-emitting diode element 101 according to Embodiment 7 described above. The GaN-based light emitting diode element 101 can be manufactured by sequentially executing the steps (A) to (G) described below.

(A) Preparation of Epi Wafer In the first step, as shown in FIG. 21A, an n-type layer 121, an active layer 122, and a p-type made of a GaN-based semiconductor are formed on an n-type conductive m-plane GaN substrate 110. An epi wafer on which the epi layer 120 including the layer 123 is formed is prepared. The thickness of the substrate 110 at this stage is typically 300 μm to 1 mm.

(B) Process of Epi Layer In this step, as shown in FIG. 21B, the epi layer 120 is processed by dry etching to form an element isolation groove G100. Then, the p-side ohmic electrode E201 and the p-side electrode pad E202 are sequentially formed on the p-type layer 123 of each light-emitting diode section partitioned by the element isolation trench G100. The order of forming the element isolation trench G100 and the p-side ohmic electrode E201 is not limited, and the p-side ohmic electrode E201 may be formed before forming the element isolation trench G100. In this example, the element isolation groove G100 has a depth reaching the n-type layer 121, but can be formed to a depth reaching the surface or the inside of the substrate 110. Preferably, after forming the element isolation trench G100, the p-side ohmic electrode E201, and the p-side electrode pad E202, the surface of the p-side ohmic electrode E201 and the exposed surface of the epi layer 120 are made of a transparent material such as SiO ₂ or SiN _x. And an insulating protective film (not shown).

(C) Substrate Thinning In this step, the back surface of the substrate 110 is ground or lapped to reduce the thickness of the substrate 110 as shown in FIG. When grinding is performed, lapping is continuously performed to reduce the roughness of the processed surface. At the time of this lapping, it is preferable to gradually reduce the particle diameter of the diamond abrasive used.
This step (C) may be performed as necessary, and may be omitted.

(D) Polishing of Backside of Substrate In this step, an acidic CMP slurry is used to polish the backside of the substrate 110 at a low polishing rate of 0.5 μm / h or less, and the range of 10 μm square measured using AFM. The arithmetic average roughness Ra is set to 0.1 nm or less. The pH of the CMP slurry is preferably less than 2. In the case where the back surface of the substrate 110 before polishing is a rough surface such as a ground surface, polishing is performed after lapping is performed as preliminary processing to reduce the roughness. At the time of this lapping, it is desirable to gradually reduce the grain size of the diamond abrasive grains to be used. After polishing, the slurry adhering to the substrate 110 is washed away with water and dried. After washing with water, organic cleaning or ultraviolet ozone cleaning may be performed.

(E) Formation of n-side electrode In this step, as shown in FIG. 22 (d), the n-side electrode E100 is formed on the entire back surface of the substrate 110 into a thin film using a vapor phase method such as vapor deposition, sputtering, or CVD. Form. Thus, after polishing the surface of the substrate 110 at a low rate using an acidic slurry, the contact resistance of the n-side electrode E100 is reduced by forming the n-side electrode E100 on the polished surface. Can do.

(F) Patterning of n-side electrode In this step, as shown in FIG. 22 (e), an n-side electrode E100 is formed by a method of protecting unnecessary portions with a mask and removing unnecessary portions by etching, that is, a subtractive method. Is patterned into a predetermined shape. Mask patterning can be performed using well-known photolithography techniques. The etching method may be either wet etching or dry etching. An etchant used in wet etching and an etching gas used in dry etching may be selected by appropriately referring to known techniques. In a preferred embodiment, after patterning the n-side electrode E100, the exposed surface of the substrate 110 is covered with an insulating protective film (not shown) made of a transparent material such as SiO ₂ or SiN _x .

(G) Dicing As the last step, as shown in FIG. 22F, the epi-wafer is cut at the position of the element isolation groove G100 formed in the epi layer 120, and the chip-like GaN-based light emitting diode element 101 is obtained.

(Method for Manufacturing GaN-Based Light Emitting Diode Device of Embodiment 8)
When manufacturing the GaN-based light-emitting diode element 102 (see FIG. 13) according to Embodiment 8, a step of processing the back surface of the substrate 110 into an uneven shape is required. This step is performed after the step of patterning the n-side electrode E100.

(Method for Manufacturing GaN-Based Light Emitting Diode Device of Embodiment 14)
In order to manufacture the GaN-based light emitting diode device 108 (see FIG. 19) according to the eighth embodiment, first, an n-type layer 121 made of a GaN-based semiconductor and an active layer 122 are formed on an n-type conductive m-plane GaN substrate 110. And an epi wafer on which the epi layer 120 including the p-type layer 123 is formed. Then, the epi layer 120 is dry-etched to form the element isolation groove G100, and the p-side electrode E200 is formed on the p-type layer 123 of each light-emitting diode section partitioned by the element isolation groove G100.

After forming the p-side electrode E200, the back surface of the substrate 110 is ground or lapped to reduce the thickness of the substrate 110. When grinding is performed, lapping is continuously performed to reduce the roughness of the processed surface. Thereafter, the back surface of the substrate 110 is polished using an acidic CMP slurry at a polishing rate as low as 0.5 μm / h or less.
The arithmetic average roughness Ra in the range of 10 μm square measured using FM is set to 0.1 nm or less. After polishing, the slurry adhering to the substrate 110 is washed away with water and dried. After washing with water, organic cleaning or ultraviolet ozone cleaning may be performed.

  Next, an n-side ohmic electrode E101 made of ITO is formed in a thin film shape on the entire back surface of the substrate 110 that has been polished using a vapor phase method such as vapor deposition, sputtering, or CVD. FIG. 23A is a cross-sectional view of the epi-wafer completed up to this step.

  In the next step, the n-side ohmic electrode E101 is patterned into a predetermined shape as shown in FIG. 23B by a method of removing unnecessary portions by etching after protecting necessary portions with a resist mask, that is, a subtractive method. To do. Patterning of the resist mask can be performed using a normal photolithography technique. Etching of ITO is preferably performed by a wet method using an aqueous iron chloride solution or hydrochloric acid as an etchant. In this wet etching, the etching time or the like is adjusted so that the unnecessary portion of ITO is not completely removed and the residue remains on the substrate 110.

  A polycrystalline TCO thin film such as ITO can increase the etching rate difference between the crystal part and the grain boundary part during wet etching by annealing after film formation to improve the crystallinity of the crystal part. . Therefore, when the n-side ohmic electrode E101 is a polycrystalline TCO film such as ITO, the TCO residue can be easily left on the substrate 110 after wet etching by heat-treating it.

  In the next step, the exposed back surface of the substrate 110 is dry-etched using chlorine gas as an etching gas while the resist mask used for protecting the n-side ohmic electrode E101 in the previous step remains as a mask. At this time, the remaining ITO residue acts as a fine mask, so that an infinite number of fine irregularities are formed on the dry-etched portion of the substrate 110 as shown in FIG.

After dry etching, an n-side electrode pad E102 is formed on the n-side ohmic electrode E101 as shown in FIG. In a preferred embodiment, thereafter, the exposed surface of the substrate 110 is covered with an insulating protective film (not shown) made of a transparent material such as SiO ₂ or SiN _x . Then, as the last step, as shown in FIG. 24E, the epi-wafer is cut at the position of the element isolation groove G100 formed in the epi layer 120, and the chip-like GaN-based light emitting diode element 108 is obtained.

(Modified embodiment)
Similar to each of the above-described embodiments, an epi-wafer in which an n-type layer made of a GaN-based semiconductor, an active layer, and a p-type layer are formed on the front surface of an m-plane GaN substrate is prepared, and the p After forming the p-side electrode on the upper surface of the mold layer, in the method for manufacturing a GaN-based light emitting diode device according to the modified embodiment, a support substrate is bonded to the epilayer side of the epiwafer with the p-side electrode interposed therebetween.
Next, the m-plane GaN substrate is ground or lapped from the back side to expose the n-type layer included in the epi layer.
Then, the exposed surface of the n-type layer is polished with an acidic CMP slurry (preferably less than pH 2) at a polishing rate as low as 0.5 μm / h or less, and in the range of 10 μm square measured using AFM. Arithmetic average roughness Ra shall be 0.1 nm or less. After polishing, the slurry adhering to the polished n-type layer surface is washed away with water and dried. After washing with water, organic cleaning or ultraviolet ozone cleaning may be performed.
Thereafter, an n-side electrode is formed on the polished n-type layer exposed surface in the same procedure as the manufacturing method according to the above-described embodiment, and then the patterning is performed.
The n-side electrode formed in this way is considered to have a low contact resistance with respect to the n-type layer.

(Disclosure of other inventions)
Those skilled in the art will understand that the invention relating to the surface treatment method, semiconductor device manufacturing method, or GaN-based light-emitting diode device described below is disclosed herein.
(A1) A first step of polishing the surface of the m-plane GaN substrate using an acidic CMP slurry at a polishing rate of 0.5 μm / h or less, and the surface of the m-plane GaN substrate following the first step And a second step of washing the surface with water.
(A2) The surface treatment method according to (a1), wherein the pH of the CMP slurry is less than 2.
(A3) The surface treatment method according to (a1) or (a2), wherein in the first step, the surface of the m-plane GaN substrate is polished so that the arithmetic average roughness Ra after polishing is 0.1 nm or less. .
(A4) An electrode forming step of forming an ohmic electrode on the surface of an n-type GaN substrate having n-type conductivity, and (a1) to (a3) as the surface finishing steps before the electrode forming step. A method for manufacturing a semiconductor element, comprising a surface treatment step of performing a surface treatment on the surface using the surface treatment method according to any one of the above.
(A5) The method for manufacturing a semiconductor element, wherein the m-plane GaN substrate having n-type conductivity has a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ .

(B1) A first step of polishing the exposed m-plane of the n-type GaN-based semiconductor using an acidic CMP slurry at a polishing rate of 0.5 μm / h or less, and the m-plane following the first step. A surface treatment method comprising: a second step of washing with water.
(B2) The surface treatment method according to (b1), wherein the pH of the CMP slurry is less than 2.
(B3) The surface treatment method according to (b1) or (b2), wherein in the first step, the m-plane is polished so that the arithmetic average roughness Ra after polishing is 0.1 nm or less.
(B4) An electrode forming step of forming an ohmic electrode on the exposed m-plane of the n-type GaN-based semiconductor, and the steps (b1) to (b3) as finishing steps of the m-plane before the electrode forming step. A method for producing a semiconductor element, comprising a surface treatment step of performing surface treatment on the m-plane using the surface treatment method according to any one of the above.
(B5) The manufacturing method according to (b4), wherein the n-type GaN-based semiconductor is an n-type GaN-based semiconductor layer formed by epitaxial growth using an m-plane GaN substrate.

(C1) An n-type layer made of a GaN-based semiconductor, an active layer, and a p-type layer are stacked in this order, and the stacking direction is parallel to the m-axis of the GaN-based semiconductor and connected to the p-type layer A p-side electrode and an n-side ohmic electrode formed on the surface of the n-type layer opposite to the active layer side, and a forward current applied to the light-emitting diode element is 20 mA. A GaN-based light emitting diode element having a forward voltage of 4.0 V or less at
(C2) An n-type layer made of a GaN-based semiconductor, an active layer, and a p-type layer are stacked in this order, and the stacking direction is parallel to the m-axis of the GaN-based semiconductor and connected to the p-type layer A p-side electrode and an n-side ohmic electrode formed on the surface of the n-type layer opposite to the surface on the active layer side, and a forward current applied to the light-emitting diode element is 60 mA. A GaN-based light-emitting diode element having a forward voltage of 4.5 V or less at the time.
(C3) An n-type layer made of a GaN-based semiconductor, an active layer, and a p-type layer are stacked in this order, and the stacking direction is parallel to the m-axis of the GaN-based semiconductor and connected to the p-type layer A p-side electrode and an n-side ohmic electrode formed on the surface of the n-type layer opposite to the surface on the active layer side, and a forward current applied to the light-emitting diode element is 120 mA. A GaN-based light-emitting diode element having a forward voltage of 5.0 V or less at the time.
(C4) An n-type layer made of a GaN-based semiconductor, an active layer, and a p-type layer are stacked in this order, and the stacking direction is parallel to the m-axis of the GaN-based semiconductor and connected to the p-type layer A p-side electrode and an n-side ohmic electrode formed on the surface of the n-type layer opposite to the active layer side, and a forward current applied to the light-emitting diode element is 200 mA. A GaN-based light-emitting diode element having a forward voltage of 5.5 V or less at the time.
(C5) An n-type layer composed of a GaN-based semiconductor, an active layer, and a p-type layer are stacked in this order, and the stacking direction is parallel to the m-axis of the GaN-based semiconductor and connected to the p-type layer A p-side electrode and an n-side ohmic electrode formed on the surface of the n-type layer opposite to the surface on the active layer side, and a forward current applied to the light-emitting diode element is 350 mA. A GaN-based light emitting diode element having a forward voltage of 6.0 V or less at
(C6) The GaN-based light-emitting diode element according to any one of (c1) to (c5), wherein an area of a surface of the n-type layer on which the n-side ohmic electrode is formed is 0.0012 cm ² or more. .
(C7) The GaN-based material according to (c6), wherein an area of the n-side ohmic electrode is 0.0012 cm ² or more and an area of a surface of the n-type layer on the side where the n-side ohmic electrode is formed. Light emitting diode element.
(C8) The surface of the n-type layer has an arithmetic average roughness Ra in the range of 10 μm square of 0.1 nm or less in at least a portion in contact with the n-side ohmic electrode, according to (c1) to (c7) The GaN-based light emitting diode element according to any one of the above.

100, 101, 102, 103, 104, 105, 106, 107, 108, 109 GaN-based light emitting diode element 110 Substrate 112a Low contact resistance region 112b High contact resistance region 120 Epi layer 121 n-type layer 122 active layer 123 p-type layer E100 n-side electrode E101 n-side ohmic electrode E102 n-side electrode pad E103 auxiliary electrode E200 p-side electrode E201 p-side ohmic electrode E202 p-side electrode pad E203 auxiliary electrode G100 element isolation trench R100 dielectric reflection film

Claims (5)

  An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a flat surface provided on the back surface of the m-plane GaN substrate A forward voltage when the forward current applied to the light emitting diode element is 20 mA is 4.0 V or less. A GaN-based light emitting diode element.   An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a flat surface provided on the back surface of the m-plane GaN substrate A forward voltage when the forward current applied to the light emitting diode element is 60 mA is 4.5 V or less. A GaN-based light emitting diode element.   An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a flat surface provided on the back surface of the m-plane GaN substrate A forward voltage when the forward current applied to the light emitting diode element is 120 mA is 5.0 V or less. A GaN-based light emitting diode element.   An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a flat surface provided on the back surface of the m-plane GaN substrate A forward voltage when the forward current applied to the light emitting diode element is 200 mA is 5.5 V or less. A GaN-based light emitting diode element.   An n-type conductive m-plane GaN substrate, a light emitting diode structure formed using a GaN-based semiconductor on the front surface of the m-plane GaN substrate, and a flat surface provided on the back surface of the m-plane GaN substrate A forward voltage when the forward current applied to the light emitting diode element is 350 mA is 6.0 V or less. A GaN-based light emitting diode element.

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