JP2004193206A - Oxide semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide semiconductor light emitting element exhibiting excellent emission efficiency in a visible light region and operating on low voltages. <P>SOLUTION: The oxide semiconductor light emitting element has a light emitting layer 3 composed of a ZnO semiconductor doped with n-type impurities Ga of a group III element at a concentration of 3×10<SP>18</SP>cm<SP>-3</SP>. When the ZnO emission layer 3 is employed, a higher emission intensity is attained as compared with a conventional light emitting element, resistance of the emission layer 3 is decreased and the operating voltage of the light emitting diode element 10 is lowered. Consequently, a light emitting element exhibiting excellent emission characteristics and operating on low voltages is attained. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device such as a light emitting diode and a semiconductor laser, and more particularly, to an oxide semiconductor light emitting device having excellent luminous efficiency and operating at a low voltage.
[0002]
[Prior art]
Zinc oxide (ZnO) is a direct transition type semiconductor having a band gap energy of about 3.4 eV, has an extremely high exciton binding energy of 60 meV, is inexpensive in raw materials, harmless to the environment and the human body, and has a simple film forming method. Therefore, there is a possibility that a light-emitting device having high efficiency, low power consumption, and excellent environmental performance can be realized.
[0003]
In the following, a ZnO-based semiconductor includes ZnO and a mixed crystal represented by MgZnO or CdZnO, which is based on ZnO.
[0004]
In a semiconductor light emitting device, in order to improve the luminous efficiency of a light emitting layer, doping with an n-type impurity or a p-type impurity is generally performed.
[0005]
For example, in a group III nitride semiconductor light emitting device used for a blue to ultraviolet light emitting device, Japanese Patent No. 2,560,963, Japanese Patent No. 2,560,964 and Japanese Patent No. 2576819 disclose an n-type impurity such as Si or p-type. There is disclosed a technique for improving luminous efficiency by doping a light emitting layer with impurities such as Zn and Mg.
[0006]
Japanese Patent Application Laid-Open No. 2001-287998 discloses a technique for improving the light emission characteristics of a ZnO-based semiconductor. According to this publication, the doping amount of the group III element is 1 × 10¹⁷~ 1 × 10¹⁸cm^-3It is shown that, by reducing the crystal defects, broad light emission on the long wavelength side is reduced, and the light emission intensity is improved by four times or more as compared with the case of non-doping.
[0007]
[Patent Document 1]
JP 2001-287998 A
[Patent Document 2]
Japanese Patent No. 2560963
[Patent Document 3]
Japanese Patent No. 2560964
[Patent Document 4]
Japanese Patent No. 2576819
[0008]
[Problems to be solved by the invention]
Blue light having a wavelength of about 430 nm corresponding to the blue light emission wavelength has low visibility (a wavelength function indicating the relationship between the brightness of monochromatic light and light energy). In the case of manufacturing a light-emitting device, it is advantageous to have a high light-emitting intensity and a light-emitting characteristic with a wide spectral half width.
[0009]
However, the conventional semiconductor light emitting device using ZnO has a first emission spectrum located in an ultraviolet light region shorter than 400 nm, has a weak emission intensity near 430 nm corresponding to a blue emission wavelength, and has a low first emission spectrum. The half width of the spectrum is narrow. For this reason, there was a problem that it was difficult to improve the emission intensity of visible light.
[0010]
Further, in the above-described conventional doping concentration range, there is a problem that the resistance of the light emitting layer is high, the operating voltage of the device is high, and the power consumption and reliability are reduced.
[0011]
In view of the above problems, an object of the present invention is to provide an oxide semiconductor light emitting device which has excellent luminous efficiency particularly in a visible light region and operates at a low voltage.
[0012]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on the emission spectrum shape having high luminance in the visible light region and the means for realizing the emission spectrum shape of a light-emitting element manufactured using a ZnO-based semiconductor. The present inventors have found that the above object can be achieved by improving the emission intensity near the emission wavelength of 430 nm in addition to the doping.
[0013]
That is, the oxide semiconductor light-emitting device of the present invention includes at least a light-emitting layer including an n-type ZnO-based semiconductor layer and a p-type ZnO-based semiconductor layer on a substrate;
In the n-type ZnO-based semiconductor layer included in the light emitting layer, an n-type impurity composed of at least one group III element contains 1 × 10¹⁸cm^-3Over 1 × 10²⁰cm^-3It is characterized by being doped at the following concentrations.
[0014]
According to the oxide semiconductor light emitting device of the present invention, the n-type ZnO-based semiconductor layer included in the light emitting layer is 1 × 10¹⁸cm^-3Over 1 × 10²⁰cm^-3Since the n-type impurity is doped in the following concentration range, the light emitting layer has higher emission intensity than the conventional one, the resistance of the light emitting layer is reduced, and the operating voltage of the light emitting element is reduced. Thus, an oxide semiconductor light-emitting element having excellent light-emitting characteristics and operating at a low voltage can be realized.
[0015]
In one embodiment, the doping concentration of the n-type impurity is 1 × 10¹⁸cm^-3Beyond 1 × 10¹⁹cm^-3It is as follows.
[0016]
According to this embodiment, in the light emitting layer doped with the n-type impurity in the doping concentration range, absorption and scattering by the doping impurity are reduced, so that the luminous efficiency can be further improved.
[0017]
In one embodiment, the oxide semiconductor light-emitting element includes at least a light-emitting layer including an n-type ZnO-based semiconductor layer and a p-type ZnO-based semiconductor layer on a substrate,
An n-type ZnO-based semiconductor layer included in the light-emitting layer is doped with an n-type impurity including at least one group III element;
The emission intensity at a wavelength of 430 nm is not less than 1/30 of the first emission spectrum peak intensity existing in a wavelength region shorter than the wavelength of 430 nm.
[0018]
According to this embodiment, since the emission intensity at a wavelength of 430 nm is 1/30 or more of the first emission spectrum peak intensity (main peak intensity), the visibility of blue emission is improved.
[0019]
Conventionally, when ZnO is used for the light emitting layer, the emission spectrum is a single-peaked spectrum having a peak near 370 nm.¹⁸cm^-3By doping at a higher concentration than the above, the half width is increased.
[0020]
In addition, by doping the light-emitting layer with an n-type impurity at a high concentration, the light-emitting intensity peak at a wavelength shorter than 430 nm may be multimodal having a plurality of peaks. Also, the manner of superposition of the multimodal peaks differs depending on the doping concentration. However, based on the strongest peak intensity among the multimodal peaks, the emission intensity at 430 nm is 1/30 or more of the above standard. If there is, an effect of the present invention, that is, an oxide semiconductor light emitting element which is excellent in luminous efficiency particularly in a visible light region and operates at a low voltage is realized.
[0021]
In one embodiment, in the oxide semiconductor light-emitting device, the light-emitting layer contains Cd.
[0022]
In this embodiment, the light emitting layer is formed of a mixed crystal of CdO and CdO._XZn_1-XO, the band gap energy decreases, and the emission peak wavelength shifts to the longer wavelength side. Therefore, a high-luminance visible light emitting element with higher visibility can be manufactured. The above Cd_XZn_1-XIn O, when the Cd composition ratio x increases and exceeds 0.25, the crystallinity of the light emitting layer deteriorates and the light emission intensity decreases. Therefore, in order to obtain blue light emission with high luminance, the Cd composition ratio x is high. Is preferably 0.25 or less.
[0023]
In one embodiment, the Group III element is at least one of Ga, Al, and In.
[0024]
In the above embodiment, the group III element functions as a donor impurity in the ZnO-based semiconductor. In particular, the elements Ga, Al, and In have high luminous efficiency and can provide a light-emitting element with high luminance.
[0025]
In a more preferred embodiment, the group III element is Ga. Ga has a particularly high activation rate, is easily doped, and hardly causes crystal defects. Therefore, a light-emitting element with higher luminance can be obtained.
[0026]
In one embodiment, the light emitting layer is doped with a p-type impurity containing at least one group I element or a group V element together with the n-type impurity. The type is n-type.
[0027]
In the above embodiment, the light emitting layer is doped with the p-type impurity together with the n-type impurity, so that the donor-acceptor pair participates in light emission. This light emission has a wide half-value width, and the light emission has a longer wavelength than in the past. Therefore, a high-luminance visible light emitting element with higher visibility can be manufactured.
[0028]
In a more preferred embodiment, the p-type impurity is N (nitrogen). N (nitrogen) has a higher activation rate than other p-type impurities, is easily doped, and hardly causes crystal defects. Therefore, a light-emitting element with higher luminance can be obtained.
[0029]
In one embodiment, the light emitting layer has a quantum well structure including a well layer and a barrier layer.
[0030]
In the above embodiment, the light emitting layer having the quantum well structure has a high light emitting efficiency, has a high light emitting intensity even with a thin layer thickness as compared with the bulk light emitting layer, and can obtain high luminance at a low operating voltage. When the light emitting layer having the quantum well structure is used as an active layer of a laser device, the optical gain increases and the oscillation threshold current can be reduced. Therefore, an oxide semiconductor light-emitting element which is more excellent in light-emitting characteristics and operates at a low voltage can be realized.
[0031]
In one embodiment, only the well layer of the light emitting layer is doped with the n-type impurity.
[0032]
In the above embodiment, the n-type impurity is doped (highly doped) only in the well layer of the light emitting layer, so that the light emitting intensity can be improved while suppressing the doping amount of the entire light emitting layer, and the crystal defects can be reduced. it can.
[0033]
In one embodiment, only the barrier layer of the light emitting layer is doped with the n-type impurity.
[0034]
In the above embodiment, since the n-type impurity is doped (highly doped) only in the barrier layer of the light emitting layer, absorption and scattering of light in the light emitting layer can be suppressed, and the operating voltage can be reduced.
[0035]
In one embodiment, the oxide semiconductor light emitting device has an n-type ZnO-based semiconductor layer sandwiching the light-emitting layer with the p-type ZnO-based semiconductor layer.
The p-type ZnO-based semiconductor layer and the n-type ZnO-based semiconductor layer sandwiching the light-emitting layer include a layer having a larger band gap energy than the light-emitting layer.
[0036]
In the above embodiment, the n-type ZnO-based semiconductor layer and the p-type ZnO-based semiconductor layer sandwiching the light-emitting layer include a layer (for example, MgZnO) having a band gap energy larger than that of the light-emitting layer. The n-type ZnO-based semiconductor layer and the p-type ZnO-based semiconductor layer have a function as a cladding layer sandwiching the light emitting layer. With this structure, injected carriers are confined in the light emitting layer, and the luminous efficiency is improved, so that high luminance can be obtained at a low operating voltage.
[0037]
Note that the n-type and p-type ZnO-based semiconductor layers may be composed of a plurality of layers having different compositions and thicknesses. In this case, a layer having a band gap larger than that of the light emitting layer is in contact with the light emitting layer. The structure provided is preferable because the effect of confining carriers can be improved.
[0038]
In one embodiment, the hole concentration of the p-type ZnO-based semiconductor layer is higher than the electron concentration of the light-emitting layer.
[0039]
According to the configuration of the above-described embodiment, a barrier between the p-type ZnO-based semiconductor layer and the n-type ZnO-based light emitting layer is increased, carrier overflow is reduced, and the effect of confining carriers in the light emitting layer is further improved. Thus, an oxide semiconductor light-emitting element which is more excellent in light-emitting characteristics and operates at a low voltage can be realized.
[0040]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
[0041]
(First Embodiment)
As an oxide semiconductor light emitting device according to a first embodiment of the present invention, an example in which a light emitting layer 3 of a ZnO-based light emitting diode device is formed of a Ga doped ZnO semiconductor will be described.
[0042]
FIG. 1 is a structural sectional view of the light emitting diode element 10 according to the first embodiment.
In the light emitting diode element 10 of the first embodiment, 5 × 10 Ga (gallium) as an n-type impurity composed of a group III element is formed on a ZnO substrate 1 having a zinc surface as a main surface.¹⁸cm^-3An n-type ZnO layer 2 serving as an n-type ZnO-based semiconductor layer having a thickness of 1 μm and doped with is doped. On the n-type ZnO layer 2, Ga¹⁸cm^-3And a ZnO light emitting layer 3 made of a 0.5 μm thick ZnO semiconductor. On this ZnO light emitting layer 3, 1 × 10 N (nitrogen) as a p-type impurity is added.²⁰cm^-3A p-type ZnO layer 4 serving as a p-type ZnO-based semiconductor layer having a thickness of 1 μm and doped with is doped.
[0043]
On the back surface of the ZnO substrate 1, an n-type ohmic electrode 5 made of Al having a thickness of 1000 ° is laminated. On the entire main surface of the p-type ZnO layer 4, a p-type translucent ohmic electrode 6 made of Ni having a thickness of 150 ° is laminated. On this p-type translucent ohmic electrode 6, a bonding Au pad electrode 7 having a thickness of 1000 ° is formed with an area smaller than that of the translucent ohmic electrode 6.
[0044]
In the light emitting diode element 10 of the first embodiment, the ZnO light emitting layer 3 is made of a ZnO semiconductor doped with an n-type impurity in a predetermined concentration range.
[0045]
The light emitting diode element 10 of the first embodiment was formed by a laser molecular beam epitaxy (hereinafter, referred to as laser MBE) apparatus 100 shown in FIG.
[0046]
First, the laser MBE device 100 will be described. In the laser MBE apparatus 100, a substrate holder 102 is disposed above a growth chamber 101 that can be evacuated to an ultra-high vacuum, and a substrate 103 is fixed to the substrate holder 102. The back surface of the substrate holder 102 is heated by the heater 104 disposed above the substrate holder 102, and the substrate 103 is heated by the heat conduction. A target table 105 is disposed directly below the substrate holder 102 at an appropriate distance, and a plurality of raw material targets 106 can be disposed on the target table 105.
[0047]
The surface of the raw material target 106 is ablated by a pulsed laser beam 108 irradiated through a view port 107 provided on the side surface of the growth chamber 101, and a plume (emitted particles) 110 of the raw material target 106 that evaporates instantaneously is placed on the substrate 103. The deposition grows a thin film. The target table 105 has a rotation mechanism, and by controlling the rotation in synchronization with the irradiation sequence of the pulsed laser beam 108, different types of raw materials from different types of raw material targets 106 can be stacked on a thin film. Become. Further, a plurality of gas introduction pipes 109 are provided in the growth chamber 101 so that a plurality of gases can be introduced, and the substrate 103 can be irradiated with an atomic beam activated by the radical cell 111.
[0048]
Next, a method of manufacturing the light emitting diode element 10 by the laser MBE apparatus 100 will be described in order.
[0049]
First, the cleaned ZnO substrate 1 was introduced into the laser MBE apparatus 100 and heated at a temperature of 700 ° C. for 30 minutes to be cleaned.
[0050]
Next, the substrate temperature was lowered to 550 ° C., and a raw material target made of non-doped ZnO single crystal and Ga₂O₃A raw material target made of a ZnO sintered body to which is added. Then, the driving cycle of the target table 105 by the rotation mechanism and the pulse irradiation cycle of the pulse laser beam 108 of the KrF excimer laser are synchronized by an external control device (not shown). Then, the two types of raw material targets 106 were alternately ablated at such a ratio as to obtain a desired Ga concentration, thereby obtaining an n-type ZnO layer 2. The pulse laser for performing this ablation is a KrF excimer laser (wavelength: 248 nm, pulse number: 10 Hz, output 1 J / cm).²) Was used. Also, during the growth of the n-type ZnO layer 2, O gas is supplied from one of the plurality of gas introduction pipes 109a.₂Gas was introduced.
[0051]
Next, the Zn doping layer 3 was formed by controlling the Ga doping concentration by the same alternate ablation technique as the formation of the n-type ZnO layer 2.
[0052]
Next, O is introduced through the gas introduction pipe 109a.₂While introducing the gas, N introduced through the gas introduction pipe 109b₂Ablation was performed using the ZnO single crystal as the raw material target 106 while irradiating the gas with plasma from the radical cell 111 to grow the p-type ZnO layer 4.
[0053]
Next, the ZnO substrate 1 was taken out of the laser MBE apparatus, and a Ni thin film was vacuum-deposited to a thickness of 150 ° to form a translucent ohmic electrode 6. The ohmic electrode 6 transmits 70% or more of the incident light.
[0054]
Finally, Au was vacuum-deposited on the translucent ohmic electrode 6 made of the Ni thin film to form a pad electrode 7, and Al was vacuum-deposited on the back surface of the ZnO substrate 1 to form an n-type ohmic electrode 5.
[0055]
The light emitting diode element 10 which is the oxide semiconductor light emitting element of the first embodiment can be formed by a molecular beam epitaxy method using a solid material or a gaseous material, a metal organic chemical vapor deposition (MOCVD) method, etc., in addition to the laser MBE method. It can be manufactured by the crystal growth technique described above. However, in the laser MBE method, the composition deviation between the raw material target and the thin film to be formed is small, and the ZnGa₂O₄It is preferable because generation of unintended by-products such as the above can be suppressed.
[0056]
The light emitting diode element 10 of the first embodiment was separated into chips, mounted on a lead frame with an Ag paste, and molded to emit light. As a result, blue-violet light with a peak emission wavelength of 380 nm was obtained.
[0057]
FIG. 3 shows an emission spectrum of the light-emitting diode element of the first embodiment at room temperature by a characteristic curve G1 drawn by a solid line. In FIG. 3, a characteristic curve G2 drawn by a broken line is an emission spectrum of the light emitting diode element of the comparative example.¹⁷cm^-3It was fabricated using a doped ZnO light emitting layer. A characteristic curve G3 drawn by a dotted line in FIG. 3 is an emission spectrum of another comparative example. This comparative example was manufactured using a non-doped ZnO light emitting layer.
[0058]
The light emitting diode element 10 of the first embodiment has a higher light emission intensity than the light emitting diode elements of the comparative example corresponding to the characteristic curves G2 and G3, the peak wavelength shifts to a longer wavelength side and the spectrum is higher than that of the comparative example. The half width is expanding. In the characteristic curve G1, a shoulder H is seen on the longer wavelength side than the peak wavelength, but the shape of the curve of the shoulder H varies depending on the doping conditions, and is substantially unimodal or shows two or more peaks. In some cases it had.
[0059]
However, in any of the spectrum shapes, when the emission intensity at the wavelength of 430 nm is 1/30 or more of the peak intensity of the first emission spectrum P1 existing on the short wavelength side, a higher emission intensity than the comparative example is obtained. In addition, the spectral half width was widened and the visibility of blue was improved.
[0060]
Next, FIG. 4 shows the result of examining the luminance and the operating voltage of the light emitting diode element of this embodiment by changing the Ga doping amount of the light emitting layer 3. In FIG. 4, the solid line is the luminance curve F1, and the broken line is the operating voltage curve F2.
[0061]
As shown by the luminance curve F1, the Ga doping amount is 1 × 10¹⁹cm^-3Up to 1 × 10²⁰cm^-3If it exceeds, it will decrease significantly. On the other hand, as shown by the operating voltage curve F2, the operating voltage is such that the Ga doping amount is 1 × 10¹⁹cm^-3Up to 1 × 10²⁰cm^-3When it exceeds, it increases remarkably.
[0062]
The reason for this is that the Ga doping amount is 1 × 10²⁰cm^-3Above, it is considered that the absorption and scattering of the light emission by the doping impurities are increased, the crystallinity is deteriorated, and the light emission efficiency and the operating voltage are deteriorated.
[0063]
From the above results, the doping amount of the n-type impurity into the light-emitting layer 3 composed of the n-type ZnO-based semiconductor layer is 1 × 10¹⁸cm^-3Over 1 × 10²⁰cm^-3The following is preferable, and 1 × 10¹⁸cm^-3Over 1 × 10¹⁹cm^-3The following is more preferred.
[0064]
By setting the doping amount of the n-type impurity in the light-emitting layer 3 as described above, the light-emitting diode element 10 as an oxide semiconductor light-emitting element which has excellent light-emitting characteristics and operates at a low voltage can be realized.
[0065]
In the first embodiment, Ga is used as the n-type impurity. However, even when other group III elements such as Al and In are used, the present invention is particularly excellent in luminous efficiency in the visible light region and operates at a low voltage. It has the effect of the invention. However, among the group III elements, Ga is preferable because it has a particularly high activation rate, is easy to dope, and hardly causes crystal defects.
[0066]
Further, when the hole concentration of the p-type ZnO layer 4 is higher than the electron concentration of the light emitting layer 3, carrier overflow can be reduced, the effect of confining carriers in the light emitting layer 3 is improved, and the light emitting characteristics are further improved. , And operate at a low voltage.
In the first embodiment, the n-type ZnO layer 2, which is an n-type ZnO-based semiconductor layer, contains 5 × 10 Ga as an n-type impurity.¹⁸cm^-3The doping concentration of the n-type impurity in the n-type ZnO layer 2 may be the same as the doping concentration of the n-type impurity in the light emitting layer 3. However, as in this embodiment, when the doping concentration of the n-type impurity in the n-type ZnO layer 2 is higher than the doping concentration of the n-type impurity in the light emitting layer 3, carrier overflow can be suppressed.
[0067]
In the first embodiment, the ZnO substrate 1 made of a ZnO single crystal having a zinc surface as a main surface is employed. However, even if a ZnO single crystal having an oxygen surface as a main surface is used as the ZnO substrate 1, the light emitting layer may be formed. The luminous efficiency of No. 3 does not change. However, by using a ZnO single crystal having a zinc surface as the main surface as the ZnO substrate 1, the carrier activation rate of the p-type ZnO layer 4 is improved, and a low-resistance p-type ZnO layer 4 is obtained, and the device resistance is reduced. Is preferred.
[0068]
Further, as the substrate 1, sapphire or LiGaO₂An insulating substrate such as SiC or a conductive substrate such as SiC or GaN can be used.
For example, when the above-mentioned insulating substrate is used as the substrate 1, the growth layer grown on the insulating substrate is etched to expose the n-type ZnO layer, and an n-type electrode is formed on the n-type ZnO layer. Just fine. Further, a contact layer may be formed on the insulating substrate using an n-type ZnO layer having a lower resistance than the n-type ZnO layer 2. Further, a buffer layer may be formed on the insulating substrate in order to obtain a growth layer having good crystallinity.
[0069]
In addition, for example, when the above-mentioned conductive substrate is used as the substrate 1, an n-type electrode can be formed on the back surface of the substrate, which is preferable because the element manufacturing process is simplified. In particular, it is preferable that the substrate 1 is a ZnO substrate having the same material system as the growth layers (the n-type ZnO layer 2 and the ZnO light emitting layer 3), since an epitaxial crystal having excellent affinity and extremely few defects can be obtained.
[0070]
It is preferable to form irregularities on the back surface of the substrate 1 by a known method such as polishing or etching in order to irregularly reflect the light emitted on the substrate 1 because the light extraction efficiency is improved.
[0071]
Further, the p-type translucent ohmic electrode 6 may be made of Pt, Pd, Au, or the like in addition to Ni. However, it is preferable that the ohmic electrode 6 is made of Ni having low resistance and good adhesion. In addition, the p-type ZnO layer 4 as a p-type ZnO-based semiconductor has a higher resistance and is less likely to spread current uniformly than the n-type ZnO layer 2 as an n-type ZnO-based semiconductor. To compensate for this, as in the first embodiment, the light-transmitting ohmic electrode 6 on the p-side is made thin and light-transmitting, and the light-transmitting ohmic electrode 6 is formed on the entire element main surface, that is, the p-type ZnO layer 4. Is preferably formed over the entire surface.
[0072]
Further, the n-type ohmic electrode 5 may be made of Ti, Cr or the like instead of Al. However, when the n-type ohmic electrode 5 is made of Al, the reflectivity of blue light to ultraviolet light is higher than when it is made of other materials such as Ti and Cr. Even so, the light extraction efficiency increases. The n-type ohmic electrode 5 made of Al may be patterned into an arbitrary shape, and the exposed back surface of the ZnO substrate 1 may be bonded to a lead frame with an Ag paste or the like. The Ag paste is preferable because the reflectivity of blue to ultraviolet light is higher and the light extraction efficiency is higher than that of the Al paste.
[0073]
The other configurations described above are arbitrary and are not limited by this embodiment.
[0074]
(Second embodiment)
Next, FIG. 5 shows a cross-sectional structure of a light emitting diode element 21 as a second embodiment of the oxide semiconductor light emitting element of the present invention. In FIG. 5, the same components as those in the first embodiment are denoted by the same reference numerals.
[0075]
In the second embodiment, an n-type MgO having a thickness of 1 μm is used instead of the n-type ZnO layer 2 having a thickness of 1 μm as an n-type ZnO-based semiconductor layer._{0 . 2}Zn_{0 . 8}The O layer 12 was formed. Further, instead of the p-type ZnO layer 4 having a thickness of 1 μm as the p-type ZnO-based semiconductor layer, a p-type MgO having a thickness of 1 μm is used._{0 . 2}Zn_{0 . 8}The O layer 14 was formed. This is different from the first embodiment.
[0076]
In the second embodiment, the p-type Mg_{0 . 2}Zn_{0 . 8}The difference from the first embodiment is that a p-type ZnO contact layer 18 is stacked on the O layer 14. Except for the above two points, the light emitting diode element 21 of the second embodiment was manufactured in the same manner as the first embodiment.
[0077]
The above n-type Mg_{0 . 2}Zn_{0 . 8}The O layer 12 contains 5 × 10 Ga as an n-type impurity composed of a group III element.¹⁸cm^-3Doped. In addition, the p-type Mg_{0 . 2}Zn_{0 . 8}The O layer 14 contains 1 × 10 N (nitrogen) as a p-type impurity.²⁰cm^-3Doped. This impurity doping is the same as in the first embodiment.
[0078]
The p-type ZnO contact layer 18 is made of p-type Mg_{0 . 2}Zn_{0 . 8}The doping concentration of the impurity N (nitrogen) was controlled so that the resistance was lower than that of the O layer 14. The thickness of the p-type ZnO contact layer 18 was 1 μm.
[0079]
When the light-emitting diode element 21 of the second embodiment was separated into chips, mounted on a lead frame with Ag paste, and molded to emit light, blue light with a light emission wavelength of 380 nm was obtained. The luminance was 30% higher and the operating voltage was 20% lower than in the first embodiment.
[0080]
In the structure of the light emitting diode element 21 of the second embodiment, the ZnO light emitting layer 3 is sandwiched between the p-type MgZnO layer 14 as the p-type ZnO-based semiconductor layer and the n-type MgZnO layer 12 as the n-type ZnO-based semiconductor layer. Thus, the p-type MgZnO layer 14 and the n-type MgZnO layer 12 have larger band gap energies than the ZnO light emitting layer 3 made of a ZnO semiconductor. With this structure, the effect of confining carriers in the ZnO light emitting layer 3 can be improved.
[0081]
In the second embodiment, the p-type ZnO contact layer 18 made of a ZnO semiconductor is formed on the p-type MgZnO layer 14 as a layer having a lower resistance than the p-type MgZnO layer 14. Therefore, forming the p-type ohmic electrode 6 on the p-type ZnO contact layer 18 is preferable because the operating voltage of the light emitting diode element 21 is reduced. Further, since the p-type ZnO contact layer 18 has a function of diffusing a current and injecting the current uniformly into the light emitting layer 3, the luminance is remarkably improved.
[0082]
(Third embodiment)
Next, FIG. 6 shows a sectional structure of a ZnO-based light emitting diode element 31 as a third embodiment of the oxide semiconductor light emitting element of the present invention. In the third embodiment, an n-type ZnO-based semiconductor is used instead of the ZnO light emitting layer 3 of the second embodiment.
Only the point that a CdZnO light emitting layer 33 made of a CdZnO semiconductor is provided is different from the second embodiment.
[0083]
That is, the CdZnO light emitting layer 33 according to the third embodiment has a Ga content of 3 × 10 3¹⁸cm^-3-Doped Ga-doped Cd with a thickness of 0.5 μm_{0 . 05}Zn_{0 . 95}It is composed of an O semiconductor.
[0084]
When the light emitting diode element 31 of the third embodiment was separated into chips, mounted on a lead frame with Ag paste and molded to emit light, the emission peak wavelength shifted to a longer wavelength side as compared with the second embodiment. As a result, blue light emission of 420 nm was obtained. For this reason, compared with the second embodiment, the visibility was improved, and the luminance was improved by 15%.
[0085]
As in the third embodiment, Ga-doped Cd_XZn_1-XIn the CdZnO light emitting layer 33 composed of an O semiconductor, the Cd composition X is preferably 0.04 or more. In order to obtain a uniform composition without deteriorating crystallinity, the Cd composition X in the CdZnO light emitting layer 33 is preferably 0.25 or less.
[0086]
(Fourth embodiment)
Next, FIG. 7 shows a cross-sectional structure of a ZnO-based light emitting diode element 41 as a fourth embodiment of the oxide semiconductor light emitting element of the present invention. In the fourth embodiment, the light emitting layer 43 is made of a CdZnO semiconductor as an n-type ZnO-based semiconductor. In other words, the light emitting layer 43 is formed of Cd doped with Ga (n-type impurity of group III element) and N (nitrogen) of p-type impurity of group V element._{0 . 05}Zn_{0 . 95}It was composed of an O semiconductor. In other respects, the light-emitting diode element 41 of the fourth embodiment was manufactured in the same manner as in the third embodiment.
[0087]
When the light emitting diode element 41 of the fourth embodiment is separated into chips, mounted on a lead frame with Ag paste and molded to emit light, the emission peak wavelength shifts to a longer wavelength side as compared with the third embodiment. As a result, blue light emission of 425 nm was obtained. Further, as compared with the third embodiment, the half width of the spectrum was increased, and the luminance was improved by 30%.
[0088]
As in the fourth embodiment, the light-emitting layer 43 composed of a CdZnO semiconductor as an n-type ZnO-based semiconductor is simultaneously doped with n-type impurity Ga and p-type impurity N to form a donor-acceptor pair. Are involved in light emission. This light emission has a wide half-value width, and the light emission has a longer wavelength than before. Therefore, a high-luminance visible light emitting element with higher visibility can be manufactured.
[0089]
In the fourth embodiment, the p-type impurity to be doped in the light emitting layer 43 made of an n-type ZnO-based semiconductor is N (nitrogen), but the p-type impurity may be a IA group element or a IB group element. , VA and VB elements can be used. However, N, which is a p-type impurity of the group V element used in the fourth embodiment, has a higher activation rate than other p-type impurities, is easy to dope, and hardly causes crystal defects. Therefore, the light emitting element 41 with higher luminance can be obtained. As the p-type impurity to be doped into the n-type ZnO-based light-emitting layer 43, Li, Ag, P, and As are preferable to N, because of their high activation rate.
[0090]
In the fourth embodiment, the p-type impurity is doped in the n-type ZnO-based light emitting layer 43 serving as an active layer doped with the n-type and p-type impurities. The conductivity type of the layer 43 is n-type. When the doping amount of the n-type ZnO-based light emitting layer 43 with the p-type impurity is large, the donor-acceptor pairs increase, thereby improving the luminous efficiency, while compensating for the n-type impurity and increasing the operating voltage. . Therefore, the doping amount of the p-type impurity into the n-type ZnO-based light emitting layer 43 is 1 × 10¹⁶cm^-3As described above, it is preferable that the ionized acceptor impurity concentration be 1/10 or less of the ionized donor impurity concentration.
[0091]
(Fifth embodiment)
Next, FIG. 8 shows a cross-sectional structure of a ZnO-based light emitting diode element 51 as a fifth embodiment of the oxide semiconductor light emitting element of the present invention. The fifth embodiment differs from the fourth embodiment in that a ZnO-based light-emitting layer 53 is provided instead of the ZnO-based light-emitting layer 43 of the fourth embodiment.
[0092]
In the fifth embodiment, as shown in FIG. 10, the ZnO-based light-emitting layer 53 is made of MgO having a thickness of 50 °._{0 . 2}Zn_{0 . 8}O barrier layer 53A and 60 ° thick Cd_{0 . 05}Zn_{0 . 95}The multi-quantum well light-emitting layer was formed by alternately stacking O well layers 53B. In the fifth embodiment, the ZnO-based light emitting layer 53 includes only 11 MgZnO barrier layers 53A and only 10 CdZnO well layers 53B. In the ZnO-based light-emitting layer 53 of the fifth embodiment, the Cd_{0 . 05}Zn_{0 . 95}In the O well layer 53B only, Ga as an n-type impurity of a group III element¹⁸cm^-3Doping.
[0093]
Except for the above, the ZnO-based light emitting diode element 51 of the fifth embodiment was manufactured in the same manner as the third embodiment.
[0094]
When the ZnO-based light-emitting diode element 51 of the fifth embodiment was separated into chips, mounted on a lead frame with Ag paste, and molded to emit light, blue light with a light emission wavelength of 410 nm was obtained, and the evaluation was performed at a drive current of 20 mA. Of the third embodiment, the luminance was 60% higher than that of the third embodiment.
[0095]
In the light emitting diode element of the fifth embodiment, the ZnO-based light emitting layer 53 is a quantum well light emitting layer, so that the light emission efficiency and the carrier confinement efficiency are improved, and the thickness of the ten well layers 53B (60 × 10 5 ) Is thinner than the thickness (0.5 μm = 5000 °) of the CdZnO light emitting layer 33 of the third embodiment, but the luminance is improved. Since the substantial band gap energy was increased by the quantum effect, the emission wavelength shifted to a shorter wavelength side than in the third embodiment.
[0096]
As described above, according to the fifth embodiment, the ZnO-based light-emitting layer 53 is a multiple quantum well light-emitting layer in which the MgZnO barrier layer 53A and the CdZnO well layer 53B are alternately stacked, so that the device characteristics are large. Improved.
[0097]
In the fifth embodiment, Ga is added only to the CdZnO well layer 53B. However, even if only the MgZnO barrier layer 53A is doped with Ga, the light emission efficiency in the visible light region is excellent and the device operates at a low voltage. An oxide semiconductor light-emitting element is obtained. On the other hand, when Ga is doped into the entire quantum well light emitting layer constituting the ZnO-based light emitting layer 53, crystallinity deteriorates and absorption by impurities increases. Therefore, in order to realize efficient light emission, only the well layer 53B or the barrier layer 53A is used. It is preferable to dope Ga. The n-type impurity of the group III element doped into the ZnO-based light-emitting layer 53 may be Al, In, or the like in addition to Ga. The doping concentration of the group III element such as n-type impurities Ga, Al, and In is 1 × 10¹⁸cm^-3Over 1 × 10²⁰cm^-3The concentration may be the following, preferably 1 × 10¹⁸cm^-3Beyond 1 × 10¹⁹cm^-3The following is assumed.
[0098]
(Sixth embodiment)
Next, FIG. 9 shows a sectional structure of a ZnO-based semiconductor laser device 60 as a sixth embodiment of the oxide semiconductor light emitting device of the present invention. In the ZnO-based semiconductor laser device 60 according to the sixth embodiment, the active layer 64 as a light-emitting layer having an n-type ZnO-based semiconductor layer is a Ga-doped CdZnO / ZnO multiple quantum well light-emitting layer.
[0099]
The semiconductor laser device 60 according to the sixth embodiment has an n-type MgO layer having a thickness of 1 μm on an n-type ZnO single crystal substrate 61 having a zinc surface as a main surface._{0 . 2}Zn_{0 . 8}O cladding layer 62, 200 nm thick n-type ZnO light guide layer 63, CdZnO / ZnO multiple quantum well active layer 64, 200 mm thick p-type ZnO light guide layer 65, 1 μm thick p-type Mg_{0 . 2}Zn_{0 . 8}An O clad layer 66 and a 0.5 μm thick p-type ZnO contact layer 67 are stacked.
[0100]
As shown in FIG. 11, the CdZnO / ZnO multiple quantum well active layer 64 includes a 50 ° thick ZnO barrier layer 64B and a 40 ° thick Cd_{0 . 05}Zn_{0 . 95}O-well layers 64A are alternately stacked. The multiple quantum well active layer 64 has two ZnO barrier layers 64B and three well layers 64A.
[0101]
In the sixth embodiment, in the multiple quantum well active layer 64, the Cd as an n-type ZnO-based semiconductor layer is used._{0 . 05}Zn_{0 . 95}Ga as an n-type impurity is only 1 × 10¹⁹cm^-3And is doped.
[0102]
As shown in FIG._{0 . 2}Zn_{0 . 8}The O-clad layer 66 is etched into a ridge stripe shape and has a ridge 66A. The region of the cladding layer 66 adjacent to the side surface of the ridge 66A is made of Mg._{0 . 3}Zn_{0 . 7}It is buried by an n-type current block layer 68 made of O.
[0103]
On the lower surface of the n-type ZnO single crystal substrate 61, an n-type ohmic electrode 69 is formed, and on the p-type ZnO contact layer 67, a p-type ohmic electrode 70 is formed.
[0104]
After fabricating the above structure of the sixth embodiment, the ZnO substrate provided with the above structure was cleaved to form an end face mirror, a protective film was vacuum-deposited, and then the ZnO-based semiconductor laser device 60 was separated into 300 μm.
[0105]
When a current was applied to the ZnO-based semiconductor laser device 60 of the sixth embodiment, blue oscillation light having a wavelength of 430 nm was obtained from the end face.
[0106]
On the other hand, Cd of the multiple quantum well active layer 64 has_{0 . 05}Zn_{0 . 95}When the O-well layer 64A was non-doped, the oscillation threshold current increased by 50%, and the operating voltage also increased by 30%. Further, the Cd of the multiple quantum well active layer 64 has_{0 . 05}Zn_{0 . 95}O well layer 64A is 1 × 10¹⁸cm^-3When Ga was used, the oscillation threshold current increased by 20% and the operating voltage also increased by 20%.
[0107]
As described above, according to the semiconductor laser device 60 of the sixth embodiment, Ga as an n-type impurity is changed to 1 × 10¹⁸cm^-31 × 10 which exceeds¹⁹cm^-3N-type Cd highly doped with a concentration of_{0 . 05}Zn_{0 . 95}By providing the CdZnO / ZnO multiple quantum well active layer 64 having the O well layer 64A, it is possible to increase the optical gain, reduce the oscillation threshold current, and realize a semiconductor laser device with a low operating voltage.
[0108]
Note that, in the sixth embodiment, the above-described effects of the present invention can be obtained even without the light guide layers 63 and 64 sandwiching the active layer 64. However, the thin active layer 64 having a quantum well is preferably formed according to the configuration because light is hardly confined and the oscillation threshold current is likely to increase.
In the sixth embodiment, in the multiple quantum well active layer 64, the Cd as an n-type ZnO-based semiconductor layer is used._{0 . 05}Zn_{0 . 95}Ga as an n-type impurity is only 1 × 10¹⁹cm^-3, But only the ZnO barrier layer 64B of the multiple quantum well active layer 64 is doped with 1 × 10 Ga as an n-type impurity.¹⁹cm^-3May be doped. In this case, absorption and scattering of light in the active layer 64 can be suppressed, and the operating voltage can be reduced. The n-type impurity of the group III element to be doped may be Al, In, or the like in addition to Ga. The doping concentration is 1 × 10¹⁸cm^-3Over 1 × 10²⁰cm^-3The concentration may be the following, preferably 1 × 10¹⁸cm^-3Beyond 1 × 10¹⁹cm^-3The following is assumed. This is the same as in the first to fifth embodiments.
Further, in the sixth embodiment, the doping concentration of the n-type impurity in the n-type MgZnO cladding layer 62, which is the n-type ZnO-based semiconductor layer, is the same as the doping concentration of the n-type impurity in the well layer 64A. However, the doping concentration of the n-type impurity in the n-type MgZnO cladding layer 62 is 1 × 10¹⁸cm^-3Over 1 × 10²⁰cm^-3In the following concentration range, when the doping concentration of the n-type impurity in the well layer 64A is higher than that, the carrier overflow can be suppressed.
[0109]
【The invention's effect】
As is clear from the above, in the oxide semiconductor light-emitting device of the present invention, the n-type ZnO-based semiconductor layer included in the light-emitting layer contains 1 × 10¹⁸cm^-3Over 1 × 10²⁰cm^-3It is doped in the following concentration range. Thus, according to the present invention, the ZnO-based light emitting layer has a higher light emission intensity than the conventional one, and the resistance of the ZnO-based light emitting layer is reduced, the operating voltage of the light emitting element is reduced, the light emitting element is excellent, and the light emitting element operates at a low voltage. An oxide semiconductor light-emitting element can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a structure of a light emitting diode element according to a first embodiment of the present invention.
FIG. 2 is a schematic view of a laser molecular beam epitaxy apparatus used for manufacturing an embodiment of the present invention.
FIG. 3 is a diagram showing an emission spectrum at room temperature of the light-emitting diode element of the first embodiment.
FIG. 4 is a diagram showing the relationship between the Ga doping amount in the light emitting layer 3, the luminance, and the operating voltage.
FIG. 5 is a sectional view illustrating a structure of a light emitting diode element according to a second embodiment of the present invention.
FIG. 6 is a sectional view illustrating a structure of a light emitting diode element according to a third embodiment of the present invention.
FIG. 7 is a sectional view illustrating a structure of a light emitting diode element according to a fourth embodiment of the present invention.
FIG. 8 is a sectional view illustrating a structure of a light emitting diode element according to a fifth embodiment of the present invention.
FIG. 9 is a sectional view illustrating a structure of a semiconductor laser device according to a sixth embodiment of the present invention.
FIG. 10 is a sectional view showing a configuration of a light emitting layer according to the fifth embodiment.
FIG. 11 is a cross-sectional view illustrating a configuration of an active layer according to the sixth embodiment.
[Explanation of symbols]
1,61 ZnO substrate
2 n-type MgZnO layer
12 n-type MgZnO layer
3 ZnO light emitting layer
4 p-type ZnO layer
14 p-type MgZnO layer
5,69 n-type ohmic electrode
6 p-type translucent ohmic electrode
70 p-type ohmic electrode
7 Pad electrode
8,67 p-type ZnO contact layer
10, 21, 31, 41, 51 light emitting diode element
53 ZnO-based light emitting layer
53A MgZnO barrier layer
53B CdZnO well layer
60 Semiconductor laser device
62 n-type MgZnO cladding layer
63 n-type ZnO light guide layer
64 quantum well active layer
64A CdZnO well layer
64B ZnO barrier layer
65 p-type ZnO light guide layer
66 p-type MgZnO cladding layer
68 n-type MgZnO current blocking layer
100 Laser MBE system
101 Growth Room
102 Substrate holder
103 substrate
104 heater
105 Target table
106 Raw material target
107 viewports
108 pulse laser light (excimer laser)
109 Gas inlet pipe
110 plume (emitted particles)
111 radical cell

Claims (13)

A light-emitting layer including an n-type ZnO-based semiconductor layer and a p-type ZnO-based semiconductor layer on a substrate,
The n-type ZnO-based semiconductor layer included in the light emitting layer is doped with an n-type impurity composed of at least one group III element at a concentration of more than 1 × 10 ¹⁸ cm ⁻³ and 1 × 10 ²⁰ cm ⁻³ or less. An oxide semiconductor light emitting device characterized by the above-mentioned. The oxide semiconductor light emitting device according to claim 1,
An oxide semiconductor light emitting device, wherein the doping concentration of the n-type impurity is more than 1 × 10 ¹⁸ cm ⁻³ and not more than 1 × 10 ¹⁹ cm ⁻³ . A light-emitting layer including an n-type ZnO-based semiconductor layer and a p-type ZnO-based semiconductor layer on a substrate,
An n-type ZnO-based semiconductor layer included in the light-emitting layer is doped with an n-type impurity including at least one group III element;
An oxide semiconductor light-emitting element, wherein a light emission intensity at a wavelength of 430 nm is 1/30 or more of a first light emission spectrum peak intensity existing in a wavelength region shorter than the wavelength of 430 nm. The oxide semiconductor light emitting device according to claim 1 or 3,
An oxide semiconductor light emitting element, wherein the light emitting layer contains Cd. The oxide semiconductor light emitting device according to claim 1 or 3,
An oxide semiconductor light-emitting element, wherein the group III element is at least one of Ga, Al, and In. The oxide semiconductor light emitting device according to claim 5,
An oxide semiconductor light emitting device, wherein the group III element is Ga. The oxide semiconductor light emitting device according to claim 1 or 3,
The light emitting layer is doped with a p-type impurity containing at least one group I element or a group V element together with the n-type impurity, and the light emitting layer has an n-type conductivity. Object semiconductor light emitting device. The oxide semiconductor light emitting device according to claim 7,
An oxide semiconductor light emitting device, wherein the p-type impurity is N. The oxide semiconductor light emitting device according to claim 1 or 3,
An oxide semiconductor light emitting device, wherein the light emitting layer has a quantum well structure including a well layer and a barrier layer. The oxide semiconductor light emitting device according to claim 9,
An oxide semiconductor light emitting device, wherein only the well layer of the light emitting layer is doped with the n-type impurity. The oxide semiconductor light emitting device according to claim 9,
An oxide semiconductor light emitting device, wherein only the barrier layer of the light emitting layer is doped with the n-type impurity. The oxide semiconductor light emitting device according to claim 1 or 3,
An n-type ZnO-based semiconductor layer sandwiching the light-emitting layer with the p-type ZnO-based semiconductor layer;
An oxide semiconductor light-emitting element, wherein the p-type ZnO-based semiconductor layer and the n-type ZnO-based semiconductor layer sandwiching the light-emitting layer include a layer having a band gap energy larger than that of the light-emitting layer. The oxide semiconductor light emitting device according to claim 1 or 3,
An oxide semiconductor light-emitting element, wherein the hole concentration of the p-type ZnO-based semiconductor layer is higher than the electron concentration of the light-emitting layer.

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