JPH09232627A - White light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white LED of high purity and reliability. SOLUTION: An GaN buffer layer 2, an N-type Al0.1 Ga0.9 N clad layer 3, an N-type GaN guide layer 4, an undoped In0.26 Ga0.74 N active layer 5, an undoped GaN barrier layer 6, an undoped In0.46 Ga0.54 N active layer 7, an undoped GaN barrier layer 8, an undoped In0.89 Ga0.11 N active layer 9, a P-type GaN guide layer 10, a P-type Al0.1 Ga0.9 N clad layer 11, a P-type GaN contact layer 12, and a P-type current diffusion layer 13 are successively laminated on a sapphire substrate 1. The three active layers different from each other in band gap energy are provided. Light rays emitted from the active layers are light of three primary colors, red light, green light, and blue light ranging in this sequence from the substrate 1, and only white light is emitted from the surface of an LED chip. In result, a white LED of high purity and reliability can be realized.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a gallium nitride-based light emitting device.

[0002]

2. Description of the Related Art With respect to domestic and outdoor lighting, white light of high purity and high reliability has not been obtained.
The one with a longer life than D has not been developed. By developing a high brightness blue LED using GaN, an outdoor full color panel display has been commercialized in combination with a red LED of AlGaAs and a green LED of GaP, but at least three or more LEDs are required to obtain white light. Need chips.

Further, since the GaP green LED has an emission wavelength of 555 nm and emits yellowish green light and has a low luminance of several hundred mcd, a full-color panel display has not been able to obtain white emission with high luminance and high purity.

Furthermore, if an LED in which red, blue, and green LED chips of three colors are resin-molded is used to emit white light, monochromatic light emission from a short distance cannot be confirmed. Further, if a light diffusing agent is used for the resin, the brightness will be lowered.

In Japanese Patent Application Laid-Open No. 7-183576, GaN is used.
A structure of a full color LED chip using is proposed. As shown in Figure 6, n-type Al0.
23In0.66 Ga0.11N cladding layer 2, n-type or p-type In0.89Ga0.11N active layer 3, p-type Al0.23In0.66
Ga0.11N cladding layer 4, n-type or p-type In0.63
Ga0.37N active layer 5, p-type Al0.23In0.66Ga0.11N cladding layer 6, n-type or p-type Al0.13In0.63Ga
A light emitting device in which an active layer 7 made of 0.24N and a cladding layer 8 made of p-type Al0.23In0.66Ga0.11N are sequentially formed.

In this light emitting device, by energizing the electrodes α, β, γ, δ provided on each clad layer, each active layer is activated.
3, 5, 7 are designed to emit light. in this way,
In order to avoid absorption of short wavelengths into long wavelengths during light emission, an active layer on the long wavelength side is formed on the substrate side.

[0007]

However, in the above-mentioned method, the clad layer 2 and the active layer 3 formed on the substrate side are formed.
Because of the large In composition, the crystallinity of the device is lowered in the initial stage of crystal growth. As a result, the active layers 3, 5, and 7 inherit the defect dislocations often generated in the early stage of growth, and the crystallinity is significantly lowered, which causes a problem in device reliability.

Further, when trying to obtain white light by the above-mentioned method, since the current does not spread sufficiently on the p side, there is monochromatic light emission of each active layer under the electrode, and it cannot be recognized as white light at a short distance. There are also problems.

It is an object of the present invention to provide a white light emitting device which solves the above problems and can realize a white light source with high brightness, high purity and high reliability.

[0010]

[Means for Solving the Problems] The bandgap energy of gallium nitride-based semiconductors is 6.2 eV for AlN to 1.
By changing _{X of} In _X Ga _1-X N (0 ≦ X ≦ 1), which is the active layer of gallium nitride-based blue LED, over a wide range up to 89 eV, theoretically band-to-band emission from 365 nm to 655 nm is possible. is there.

First, in order to solve the problem of the white light emitting device, the present invention provides In _X Ga _1-X N (0 ≦ X ≦ 1) and Al _Y Ga _1-Y N (0
This is a white light emitting device in which three active layers with different bandgap energies are formed in a gallium nitride-based LED composed of ≦ Y ≦ 1) and the bandgap energies of each active layer are increased toward the substrate. .

Further, according to the present invention, the In composition of the active layer is different.
It is a white light emitting device having an MQW structure, and the thickness of each of the active layer and the barrier layer is up to several tens of A, with 100 A being the upper limit.

In forming the active layer, the present invention provides 6H-SiC.
When the off-substrate of the (0001) plane of the substrate is used, the incorporation of In increases and the In composition of the active layer can be increased. In particular, it is preferable to use a substrate inclined in the [11-20] direction from the plane orientation of the (0001) plane substrate.

Next, as a method of solving the problem of the processing step of the epi-wafer, the present invention applies a resist to the epi-surface in order to alleviate mechanical damage on the epi-surface due to polishing of the sapphire substrate, After curing in a baking oven to form a protective film, the epi surface side is attached to the glass plate with wax.

As a method of solving the problem of the light emitting element assembling process, the present invention produces an LED by using a double-sided substrate of sapphire, and the substrate side of the LED chip is mounted on the top surface and the epi side is mounted on the lead frame. It is characterized by

Further, in order to prevent the surface oxidation of the LED, the present invention mounts the LED chip using a SiC substrate (just substrate or off-substrate) or a sapphire substrate on the reflecting mirror, and then, inside the reflecting mirror, the SiO chip of the sol gel is mounted together with the chip. It is characterized by being filled with ₂ .

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

(Embodiment 1) FIG. 1 shows an element structure of an LED as an example of a light emitting element.

First, crystal growth is performed by MOCVD. FIG. 1 (a) shows the case where a sapphire substrate is used. On sapphire substrate 1, n-type GaN buffer layer 2, n-type Al0.1Ga0.9N cladding layer 3, n-type GaN guide layer 4, undoped In0.26Ga0.74
N active layer 5, AND-type GaN barrier layer 6, AND-type In0.46
Ga0.54N active layer 7, AND-GaN barrier layer 8, AND-AND
In0.89Ga0.11N active layer 9, p-type GaN guide layer 10, p-type Al0.1Ga
The 0.9N cladding layer 11, the p-type GaN contact layer 12, and the p-type current diffusion layer 13 are sequentially laminated. After the crystal growth, annealing is performed in a N ₂ atmosphere.

Here, TMG (trimethylgallium), TMA (trimethylaluminum), and TMI (trimethylindium) are used as the group III raw material, and NH ₃ is used as the group V raw material.
The n-type dopant is Si and SiH ₄ is used as a source gas, and the p-type dopant is Mg and Cp ₂ Mg. Other n-type dopants
Ge, Te, Se, and p-type dopants are C, Zn, Ca, Sr.
There is.

In the device structure of FIG. 1, the band gap energy is 2.75 eV in the active layer 5, 2.38 eV in the active layer 7, and 2.0 eV in the active layer 9. That is, at the emission wavelength, the active layer 5
The thickness is 450 nm, the active layer 7 is 520 nm, and the active layer 9 is 620 nm.

The electrode process of FIG. 1 (a) is performed according to the following procedure. As shown in FIG. 2, (1) the SiO ₂ layer 16 is formed on the entire surface of the epitaxial layer 200. Here, the substrate is omitted. (2) The resist 202 is selectively formed by patterning the portion where the p-side current diffusion layer 13 is formed by photolithography. (3) Patterned SiO ₂
Is removed, (4) Au / Ni203 is vapor-deposited, and (5) lift-off is performed to remove the Au / Ni203 and the resist 202 other than the p-side current diffusion layer.

Next, (6) SiO _{2 is} removed, (7) SiO ₂ 204 is vapor-deposited on the entire surface, (8) the etched portion of the epi is patterned by photolithography, and ( ₂ ) the etched portion of the epi of the SiO ₂ is etched. Removal, (10) Resist removal, (11) ECR-REBE
Alternatively, the crystal is etched by RIE to the n-type Al0.1Ga0.9N cladding layer, (12) SiO _{2 is} removed, (13) SiO _{2 is formed on the} entire surface of the epi.
(14) n-side electrode part is patterned by photolithography, (15) Al is vapor-deposited, (16) lift-off is performed, Al other than the n-side electrode is removed, (17) resist is removed,
(18) Sinter of the electrode, (19) Photolithography of the p-side electrode, (20) Removal of SiO ₂ from the p-side electrode, (21) Au
/ Ni is vapor-deposited, and (22) lift-off is performed to remove Au / Ni and the resist other than the n electrode.

Through the above steps, the p-type Au / Ni current diffusion layer 13, the p-type Au / Ni electrode 14, the n-side Al electrode 15, and the SiO ₂ protective film 16 shown in FIG. 1A are formed.

The wafer processing step is performed according to the following procedure as shown in FIG. (1) Resist coating on the entire surface of the wafer on which the epitaxial layer after electrode formation is formed, (2)
Harden in a baking oven, (3) apply stick wax to the glass plate, (4) stick the front side of the epi-wafer, and (5) polish the substrate side with a diamond powder. After polishing the epi-wafer, the stick wax is melted to remove the stick wax and the resist on the surface of the epi-wafer.

Next, (6) the substrate side of the epi wafer is attached to the adhesive sheet, and (7) a scriber is used to dig a groove on the epi side to a chip size. Then, (8) an adhesive sheet is attached on the epi side of the epi wafer, and a groove is also formed on the substrate side this time along the groove formed on the epi surface. At this time, using a dicing saw, (9) Finally, chip separation is performed.

As shown in FIG. 4, (1) the separated chips are taken with vacuum tweezers and mounted on a lead frame with Ag paste. At this time, it is desirable to provide a reflecting mirror on the lead frame.

Here, the Ag paste is cured. Next, (3) resin molding is performed to cure the resin. Then (4) the lead frame is separated and soldered to complete the LED.

This white light emitting element can be used alone as a white point light source. Also, by combining multiple white LEDs, it can be used as a light source for home or outdoor lighting, and its applications are wide.

Crystal growth process up to actual LED manufacturing,
The electrode process, processing process, and assembly process are also easy. Ga
In the assembly process of the N blue LED, the LED chip after dicing is mounted on the lead frame by a method in which the electrode side is usually the top surface and a wire is stretched on one of the electrodes, so there is little wire breakage.

(Embodiment 2) When a SiC crystal is used as a substrate, crystal growth starts with an n-type AlN buffer layer 2'on an n-type SiC substrate 1 ', as shown in FIG. 1 (b). n-type Al0.1G
a0.9N clad layer 3, n-type GaN guide layer 4, and InP In0.2
6Ga0.74N active layer 5, AND-GaN barrier layer 6, AND-
In0.46Ga0.54N active layer 7, AND-type GaN barrier layer 8, AND-type In0.89Ga0.11N active layer 9, p-type GaN guide layer 10, p
-Type Al0.1Ga0.9N cladding layer 11 and p-type GaN contact layer 12
Grow.

The electrode process is performed from (1) to (5) in FIG. A p-side resist is applied over the entire surface to form an electrode pattern on the back surface of the substrate, and then the p-side resist is removed. The epi-finished wafer is subjected to steps (6) to (9) in FIG. 3 and assembled as shown in (3) in FIG.

FIG. 5 (2) shows a reflecting mirror of the LED chip.
In most LEDs, the inside of this reflector is filled with resin. Since the resin contains Br, Cl _{2 and the} like and also allows water to pass through, the inside of the reflecting mirror was filled with SiO ₂ of sol-gel instead of the resin and cured in order to prevent oxidation of the electrode.
Since sol-gel SiO ₂ is transparent and has no impurities that cause electrode oxidation, the reliability of the LED can be improved.

[0034]

As described above, according to the present invention, in the white light emitting device, the crystallinity of the LED device can be improved, uniform white light can be efficiently extracted, and the oxidation of the electrode can be suppressed to achieve the white light emission. The reliability of the device can be improved.

Thus, the white light emitting element realizes a white light source of high brightness and high reliability with only one chip. In addition, the three InGaN layers, which are the light emitting layers, individually emit blue, green, and red light, respectively, but when light is obtained from the substrate side or the epi side, a uniform white light is obtained by the color mixture of these light emissions. .
Therefore, by combining a plurality of light emitting elements for the white light source, it can be used as highly reliable home lighting or outdoor lighting. A single light emitting element can also be used as a white point light source.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a white LED element according to an embodiment of the present invention.

FIG. 2 is a diagram showing an electrode process of a white LED element according to an embodiment of the present invention.

FIG. 3 is a diagram showing a white LED element substrate polishing step and a white LED element chip processing step according to an embodiment of the present invention.

FIG. 4 is a diagram showing an assembly of a white LED according to an embodiment of the present invention.

FIG. 5 is a diagram showing a method of mounting a white LED element according to an embodiment of the present invention.

FIG. 6 is a structural cross-sectional view of a conventional light emitting device.

[Explanation of symbols]

1 sapphire (0001) substrate 2 AND-type GaN buffer layer 3 n-type Al0.1Ga0.9N cladding layer 4 n-type GaN guide layer 5 AND-type InGaN layer 6 AND-type GaN barrier layer 7 AND-type InGaN layer 8 AND -Type GaN barrier layer 9 and-type InGaN layer 10 p-type GaN guide layer 11 p-type Al0.1Ga0.9N cladding layer 12 p-type GaN contact layer 13 p-type Au / Ni current spreading electrode 14 p-type Au / Ni electrode 15 n-type Al electrode 16 SiO ₂ protective film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Ishibashi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A substrate, an active layer formed on the substrate, and barrier layers formed on both sides of the active layer, wherein the barrier layer comprises Al _X Ga _{1 -X} N (0 ≦ X ≦ 1 ), The active layer is composed of In _Y Ga _1-Y N (0 ≦ Y ≦ 1), and the active layer is composed of at least three layers having different bandgap energies. The white light-emitting device characterized in that the band gap energy of each layer becomes larger as it gets closer to the substrate. 2. The white light emitting device according to claim 1, wherein the white light emitting device has a multiple quantum well structure in which the In composition of each active layer is different. 3. The white light emitting device according to claim 1, wherein an off-substrate of 6H—SiC (0001) is used as the substrate. 4. A method for processing an epi-wafer of a light-emitting element, which comprises using a sapphire substrate and, when polishing the back surface of the substrate, applying a resist to an epitaxial surface and curing the resist. 5. A light emitting device having a structure in which a double side polished sapphire substrate is used, the substrate side of the light emitting device chip is mounted on the top surface, and the epi side is mounted on a lead frame, and wire bonding is not required. 6. A SiC substrate or a sapphire substrate is used.
When mounting the light emitting element chip on the reflector,
Sol-gel SiO2 inside the reflector to protect _TwoBuried in
A method for assembling a light emitting device, which comprises: