JPH10303459A - Gallium nitride based semiconductor light emitting element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent laser oscillation characteristics which are uniform in a substrate wafer surface, by defining the thickness of a substrate at the time of forming a quantum well structure active layer composed of nitride semiconductor containing indium and gallium. SOLUTION: The thickness of a semi-insulating GaN substrate at the time of forming a quantum well structure active layer 6 is made thicker than or equal to 5 μm and thinner than or equal to 50 μm, and temperature difference between the bottom surface and the upper surface of a substrate 1 at the time of growing crystal of InGaN is cancelled. The warp of a substrate wafer at the time of crystal growth is restrained, so that the whole bottom surface of the substrate wafer comes into contact with a heat generating member, and the distribution of surface temperature in the substrate wafer surface is restrained. As a result, the distribution of light emitting characteristics from the quantum well structure active layer 6 is improved, and a gallium nitride based semiconductor laser element wherein oscillation wavelength is uniform in the substrate wafer surface and oscillation threshold current value is low, and a gallium nitride based light emitting diode element wherein emission wavelength is uniform in the substrate wafer surface are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride based semiconductor light emitting device and a method of manufacturing the same, and more particularly, to a gallium nitride based light emitting device having a quantum well structure active layer made of a nitride semiconductor and a method of manufacturing the same.

[0002]

2. Description of the Related Art A gallium nitride based semiconductor (GaInAlN) is used as a semiconductor material for a semiconductor laser device (LD) or a light emitting diode device (LED) having an emission wavelength in a wavelength range from ultraviolet to green. A sapphire substrate, a GaN substrate, or the like is used as a substrate for manufacturing these light-emitting elements, and a metal organic chemical vapor deposition (MOCVD) or a molecular beam epitaxy (MBE) is formed on these substrates. A light emitting portion made of a gallium nitride-based semiconductor is formed by a vapor phase growth method such as described above. When a gallium nitride-based semiconductor is formed by a vapor phase growth method using a sapphire substrate, the thickness of the substrate is, for example, disclosed in
No. 166923, and usually 300 to 5
A thickness of 00 μm was used. When a GaN substrate is used, it is described in, for example, JP-A-7-94784, and the thickness of the substrate when a gallium nitride-based semiconductor is formed by a vapor phase growth method is not particularly limited.
μm to 500 μm have been used as preferred thicknesses.

On the other hand, recently, a quantum well structure has been used as an active layer of such a gallium nitride based semiconductor light emitting device. For example, a blue LD is Applied
Physics Letters, vol. 69, N
o. 10, p. 1477-1479,
FIG. 7 shows a cross-sectional view thereof. In FIG. 7, 101 is a sapphire substrate, 102 is a GaN buffer layer, and 103 is n-
GaN contact layer 104 is n-In _0.05 Ga _0.95 N
Layer 105, n-Al _0.05 Ga _0.95 N cladding layer, 10
6 is an n-GaN guide layer, 107 is a multiple quantum well structure active layer composed of an In _0.2 Ga _0.8 N quantum well layer and an In _0.05 Ga _0.95 N barrier layer, 108 is a p-Al _0.2 Ga _0.8 N layer,
109 is a p-GaN guide layer, 110 is p-Al _0.05 G
a _0.95 N cladding layer, 111 is a p-GaN contact layer, 112 is a p-side electrode, 113 is an n-side electrode, 114 is S
It is an iO ₂ insulating film. Here, the multi-quantum well structure active layer 107 is composed of 5 nm thick In _0.2 Ga _0.8 N quantum well layers.
The barrier layer is composed of a total of 9 layers, that is, four layers of In _0.05 Ga _0.95 N barrier layers having a thickness of 6 nm, and quantum well layers and barrier layers are formed alternately. The temperature during the crystal growth is 510 ° C. for the GaN buffer layer 102, and the multiple quantum well structure active layer 1
07 is 830 ° C., and other layers are 1020 ° C. In addition, Japanese Patent Application Laid-Open No. 8-316528 similarly discloses a blue LD using a gallium nitride-based semiconductor having a quantum well structure active layer. Was created without particular attention.

A blue LED is described, for example, in the above-mentioned Japanese Patent Application Laid-Open No. 8-316528, and a cross-sectional view thereof is shown in FIG. 8, 121 is a sapphire substrate, 122 is a GaN buffer layer, 123 is an n-GaN contact layer, 124 is an n-Al _0.3 Ga _0.7 N second n-type cladding layer, and 125 is n-In _0.01 Ga _0.99 GaN first n
Type cladding layer 126 is 3 nm thick In _0.05 Ga _0.95 N
Single quantum well structure active layer, 127 is p-In _0.01 Ga
_0.99 GaN first p-type cladding layer, 128 is p-Al _0.3
Ga _0.7 N second p-type cladding layer, 129 is a p-GaN contact layer, 130 is a p-side electrode, and 131 is an n-side electrode. The temperature during the growth of these crystals depends on the GaN buffer layer 1
22 is 500 ° C., and the single quantum well structure active layer 126 is 80 ° C.
The temperature is 0 ° C., and that of each of the other layers is 1050 ° C. Also in such a blue LED, the thickness of the substrate at the time of crystal growth has been produced without particular consideration.

[0005]

However, conventional blue LDs and blue LED elements using a quantum well structure active layer have a very large distribution of light emission characteristics in the plane of a substrate wafer used during crystal growth. There was a problem. That is, in a blue LD, the oscillation wavelength greatly differs between the central portion and the peripheral portion of the substrate wafer, and the yield for obtaining a desired oscillation wavelength is greatly reduced. For example, when a sapphire substrate having a diameter of 2 inches is used, the oscillation wavelength has a difference of 150 nm between the central portion and the peripheral portion of the substrate wafer. Furthermore, the conventional blue LD has an oscillation threshold current value of 1
Since it is as high as 00 mA or more, it has been necessary to drastically reduce the oscillation threshold current value for practical use for information processing of optical disks and the like.

Although blue LEDs have already been put into practical use, the emission wavelengths are significantly different between the central portion and the peripheral portion of the substrate wafer as in the case of the blue LD, and the yield for obtaining the desired emission wavelength is greatly reduced. There is a problem of doing it. LEs with the same emission wavelength, like a large full-color display using LEDs
In an application that requires a large amount of D, if the yield of blue LEDs is reduced due to the large in-plane distribution of the emission wavelength, the cost of a full-color display will increase. For this reason, realization of a blue LED that can be manufactured with the same emission wavelength with high yield has been desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and solves the above-mentioned problems in the gallium nitride-based semiconductor light emitting device to provide a semiconductor laser having uniform and good laser oscillation characteristics within the surface of a substrate wafer. It is an object of the present invention to provide an element and a method of manufacturing the same, and a light emitting diode element having a uniform emission wavelength within a substrate wafer surface and a method of manufacturing the same.

[0008]

In order to achieve the above object, a gallium nitride based semiconductor light emitting device according to the present invention is sandwiched between a cladding layer and / or a guide layer made of a nitride semiconductor by a vapor growth method. It is manufactured by setting the thickness of a substrate when forming a quantum well structure active layer made of a nitride semiconductor containing at least indium and gallium to 5 μm or more and 50 μm or less.

In finding such a present invention,
The present inventor has conducted a detailed investigation on the cause of the problem in the conventional device, and as a result, the distribution of the surface temperature within the surface of the substrate wafer during the crystal growth when forming the quantum well layer revealed that It was found that a distribution of the light emission characteristics occurred in the inside. That is, I used as a quantum well layer in a gallium nitride based semiconductor light emitting device
In the nGaN material, the In composition greatly changes depending on the temperature of the substrate surface on which InGaN is formed. Especially InGaN
Immediately after the crystal growth of
The change in n composition is large. Therefore, when a quantum well layer having a very small thickness is formed of InGaN,
The effect immediately after starting the crystal growth of GaN is not significant,
It has been found that when the substrate surface temperature decreases, the In composition rapidly increases. In InGaN materials, I
Since the emission wavelength changes depending on the n composition, the emission wavelength becomes longer as the In composition increases.

Further, it has been found that the distribution of the surface temperature in the substrate wafer surface is affected by uneven heat conduction due to the warpage of the substrate during crystal growth. In crystal growth of a gallium nitride based semiconductor, the temperature of the substrate wafer is set to 500 ° C. to 110 ° C.
Although the crystal growth is performed at 0 ° C., the temperature of the substrate is increased by heat conduction from a heating element in contact with the bottom surface of the substrate to increase the temperature of the substrate. In this case, in a conventional gallium nitride based semiconductor light emitting device having a substrate thickness of 50 μm or more, a temperature difference occurs between the bottom surface and the surface of the substrate because the substrate is thick, and the bottom surface has a higher temperature than the surface. . As a result, the bottom surface of the substrate has a larger thermal expansion than the surface, and the substrate wafer 130 is warped as shown in FIG. 9, and only the center portion is in contact with the heating element 131 and the peripheral portion is separated from the heating element. It will be in a state. Therefore, heat from the heating element is less likely to be transmitted to the peripheral portion, and the temperature of the peripheral portion is lower than that of the central portion. For this reason, when InGaN is crystal-grown, the In composition becomes large in the peripheral portion, causing a distribution of the light emission characteristics in the plane of the substrate wafer.

That is, in a blue LD, the oscillation wavelength is InG.
Since the In composition of the aN quantum well structure active layer is determined by the In composition in the central portion and the peripheral portion of the substrate wafer, the oscillating wavelength varies greatly due to the difference in In composition, and the yield for obtaining a desired oscillating wavelength is greatly reduced. I was Furthermore, the In inside the resonator structure of one blue LD element also
Since the distribution of the In composition of the GaN quantum well layer occurs,
The optical gain obtained at a constant emission wavelength is reduced, and the oscillation threshold current is increased. On the other hand, the emission wavelength of the blue LED is significantly different between the central portion and the peripheral portion of the substrate wafer, similarly to the blue LD, and the yield for obtaining the desired emission wavelength has been greatly reduced.

Therefore, according to the present invention, a quantum well structure active layer made of a nitride semiconductor containing at least indium and gallium sandwiched between a clad layer and / or a guide layer made of a nitride semiconductor is formed by a vapor phase growth method. By reducing the thickness of the substrate at this time to 5 μm or more and 50 μm or less, the temperature difference between the bottom surface and the surface of the substrate when growing InGaN crystal is eliminated, and the warpage of the substrate wafer during crystal growth is suppressed. Since the substrate wafer comes into contact with the heating element on the entire bottom surface, the distribution of the surface temperature in the surface of the substrate wafer was suppressed.

Further, the warpage of the substrate causing the surface temperature distribution in the surface of the substrate wafer is caused not only by the thickness of the substrate during crystal growth but also by the coefficient of thermal expansion between the gallium nitride based semiconductor formed on the substrate and the substrate. It is also caused by the difference. That is, as in the conventional example, after forming a cladding layer or the like made of a gallium nitride based semiconductor on a substrate at about 1050 ° C.,
When the substrate temperature is lowered to about 800 ° C. to form a GaN quantum well structure active layer, the substrate warps due to the difference in thermal expansion coefficient between the substrate and the gallium nitride based semiconductor formed on the substrate, This caused a surface temperature distribution in the plane of the wafer.

Therefore, according to the present invention, by using gallium nitride as the substrate, the difference in the coefficient of thermal expansion between the semiconductor layer formed on the substrate and the substrate is reduced, and the warpage of the wafer due to thermal strain is suppressed. The surface temperature distribution in the plane of the wafer was further improved.

As a result, the gallium nitride-based semiconductor laser device having an improved emission characteristic distribution from the InGaN quantum well structure active layer, a uniform oscillation wavelength within the substrate wafer surface and a low oscillation threshold current value, and a substrate wafer surface A gallium nitride-based light-emitting diode device having a uniform emission wavelength within the device was realized.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a sectional view showing a gallium nitride based semiconductor laser device according to a first embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a portion A in FIG. . In this figure, 1 has a c-plane as a surface and a thickness of 40 μm.
m, a semi-insulating GaN substrate having a diameter of 2 inches, 2 a non-doped GaN buffer layer, 3 an n-GaN n-type contact layer, 4 an n-Al _0.1 Ga _0.9 Nn clad layer, 5
Is an n-GaN guide layer, 6 is a multiple quantum well structure active layer composed of two In _0.2 Ga _0.8 N quantum well layers 14 and one In _0.05 Ga _0.95 N barrier layer 15, and 7 is Al _0.2 Ga _0.8
N evaporation prevention layer, 8 is a p-GaN guide layer, 9 is p-Al
_0.1 Ga _0.9 Np-type clad layer, 10 is a p-GaN p-type contact layer, 11 is a p-side electrode, 12 is an n-side electrode, and 13 is a SiO ₂ insulating film.

In this embodiment, the semi-insulating GaN substrate 1
Was set to 40 μm, but the thickness is not particularly limited as long as it is between 5 μm and 50 μm. The surface of the substrate may have another plane orientation such as the a-plane.

The non-doped GaN buffer layer 2 is for preventing the gallium nitride based semiconductor light emitting portion formed thereon from deteriorating due to the deterioration of the surface state of the semi-insulating GaN substrate 1. The buffer layer 2 may not be provided as long as the surface state of the insulating GaN substrate 1 is kept good. The material of the buffer layer 2 is not limited to GaN as long as a gallium nitride-based semiconductor can be epitaxially grown thereon.
N or AlGaN ternary mixed crystal may be used.

N-type cladding layer 4 and p-type cladding layer 9
Is an AlG having an Al composition other than n-Al _0.1 Ga _0.9 N
An aN ternary mixed crystal may be used. In this case, when the Al composition is increased, the energy gap difference and the refractive index difference between the active layer and the cladding layer increase, and carriers and light are effectively confined in the active layer, further reducing the oscillation threshold current and improving the temperature characteristics. I can do it. Also, if the Al composition is reduced to such an extent that the confinement of carriers and light is maintained, the mobility of carriers in the cladding layer increases, and thus there is an advantage that the device resistance of the semiconductor laser device can be reduced. Further, these cladding layers may be quaternary or higher mixed crystal semiconductors containing trace amounts of other elements, and the composition of the mixed crystals in the n-type cladding layer 4 and the p-type cladding layer 9 may not be the same.

The guide layers 5 and 8 are made of a material whose energy gap has a value between the energy gap of the quantum well layer constituting the multiple quantum well structure active layer 6 and the energy gap of the cladding layers 4 and 9. If so, other materials such as a ternary mixed crystal such as InGaN or AlGaN or an InGaAlN quaternary mixed crystal may be used without being limited to GaN.
It is not necessary to dope the entire guide layer with a donor or an acceptor.
Only a part of the side may be non-doped, and further, the entire guide layer may be non-doped. In this case, there are advantages that the number of carriers existing in the guide layer is reduced, light absorption by free carriers is reduced, and the oscillation threshold current can be further reduced.

The two-layer In _0.2 Ga _0.8 N quantum well layer 14 constituting the multi-quantum well structure active layer 6 and the single layer In _0.05 G
The composition of the a _0.95 N barrier layer 15 may be set according to the required laser oscillation wavelength. If the oscillation wavelength is desired to be longer, the In composition of the quantum well layer 14 is to be increased, and if the shorter wavelength is desired, the quantum well layer 14 is required. Is reduced. Further, the quantum well layer 14 and the barrier layer 15 may be a quaternary or higher mixed crystal semiconductor containing a small amount of another element in the InGaN ternary mixed crystal. Further, the barrier layer 15 may simply use GaN.

Next, a method for fabricating the gallium nitride based semiconductor laser will be described with reference to FIGS. In the following description, the case where MOCVD (metal organic chemical vapor deposition) is used is shown, but any growth method capable of epitaxially growing GaN may be used, such as MBE (molecular beam epitaxy) or HDVPE (hydride vapor phase epitaxy). Other vapor phase epitaxy methods such as the method described above.

First, trimethyl gallium (TMG) is placed on a semi-insulating GaN substrate 1 having a c-plane as a surface, a thickness of 40 μm, and a diameter of 2 inches, which is placed on a heating element in a predetermined growth furnace. Non-doped GaN buffer layer 2 at a growth temperature of 600 ° C. using ammonia and ammonia (NH ₃ ) as raw materials.
Is grown to 35 nm.

Next, the growth temperature is raised to 1050 ° C., and a 3 μm-thick Si-doped n-GaN n-type contact layer 3 is grown using TMG, NH ₃ and silane gas (SiH ₄ ) as raw materials. Subsequently, trimethyl aluminum (TMA) was added to the raw material, and the growth temperature was 1050 ° C.
0.7 μm thick Si-doped n-Al _0.1 Ga
_{A 0.9} Nn-type cladding layer 4 is grown. Subsequently, the TMA is removed from the raw material, and the Si-doped n-GaN guide layer 5 having a thickness of 0.05 μm is grown at a growth temperature of 1050 ° C.

Next, the growth temperature is lowered to 800 ° C.
, NH ₃ , and trimethylindium (TMI) as raw materials and an In _0.2 Ga _0.8 N quantum well layer (5 nm thick)
14, In _0.05 Ga _0.95 N barrier layer (5 nm thick) 15,
An In _0.2 Ga _0.8 N quantum well layer (thickness: 5 nm) 14 is sequentially grown to form a multiple quantum well structure active layer (total thickness: 15 nm) 6. Further, using TMG, TMA and NH ₃ as raw materials, an Al _0.2 Ga _0.8 N evaporation preventing layer 7 having a thickness of 10 nm is grown at a growth temperature of 800 ° C.

Next, the growth temperature is raised again to 1050 ° C., and TMG, NH ₃ , and cyclopentadienyl magnesium (Cp ₂ Mg) are used as raw materials to a thickness of 0.05 μm.
An m-doped Mg-doped p-GaN guide layer 8 is grown. Subsequently, TMA was added to the raw material, and the growth temperature was kept at 1050 ° C., and the Mg-doped p-Al _0.1 Ga _0.9 layer having a thickness of 0.7 μm was formed.
The Np-type cladding layer 9 is grown. Subsequently, except that TMA was removed from the raw material, the growth temperature was kept at 1050 ° C. and the thickness was 0.2 mm.
A μm Mg-doped p-GaN p-type contact layer 10 is grown to complete a gallium nitride based epitaxial wafer.

Thereafter, the wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to lower the resistance of the Mg-doped p-type layer.

Further, the n-type p-GaN p-type contact layer 10 is stripped from the outermost surface of the p-GaN p-type contact layer 10 by a conventional photolithography and dry etching technique.
-Etching is performed until the GaN n-type contact layer 3 is exposed. Next, using the same photolithography and dry etching techniques as described above, the p-GaN p-type contact layer is formed on the outermost surface of the remaining p-GaN p-type contact layer 10 so as to form a ridge structure in a stripe shape having a width of 5 μm. 10 and p-Al _0.1 Ga _0.9 Np type clad layer 9 are etched.

Subsequently, a 200 nm thick SiO ₂ insulating film 13 is formed on the side surfaces of the ridge and on the surface of the p-type layer other than the ridge. A p-side electrode 11 made of nickel and gold is formed on the surfaces of the SiO ₂ insulating film 13 and the p-GaN p-type contact layer 10, and an n-GaN n-type contact layer 3 exposed by etching is formed on the surface of the n-GaN n-type contact layer 3. The side electrode 12 is formed to complete a gallium nitride based LD wafer.

Thereafter, the wafer is cleaved in a direction perpendicular to the ridge stripe to form a laser cavity end face.
It is further divided into individual chips. Then, each chip is mounted on a stem, each electrode is connected to a lead terminal by wire bonding, and a gallium nitride based semiconductor laser device is completed.

The blue LD device manufactured as described above has the laser characteristics of an oscillation wavelength of 430 nm and an oscillation threshold current of 40 mA. Further, the distribution of the oscillation wavelength in the plane of the substrate wafer was reduced, and the difference in the oscillation wavelength between the central portion and the peripheral portion of the wafer, which was conventionally 150 nm, was reduced to 10 nm. Thus, according to the present invention, InGaN
The distribution of the emission characteristics from the quantum well active layer was improved, and a gallium nitride based semiconductor laser device having a uniform oscillation wavelength and a low oscillation threshold current value within the surface of the substrate wafer was realized.

FIG. 3 shows the difference in oscillation wavelength between the center and the periphery of the wafer due to the thickness of the semi-insulating GaN substrate having a diameter of 2 inches in the gallium nitride based semiconductor laser device. A graph showing the change and the change of the oscillation threshold current value is shown. The structure of each semiconductor laser is the same as the gallium nitride based semiconductor laser device according to the first embodiment of the present invention except that the thickness of the GaN substrate during crystal growth is different. As you can see from this figure,
When the thickness of the GaN substrate during crystal growth exceeds 50 μm, the in-plane distribution of the oscillation wavelength increases rapidly, and the oscillation threshold current value also increases. Therefore, the reason why the emission wavelength is uniform in the wafer surface and a low oscillation threshold current value can be obtained is that the thickness of the GaN substrate during crystal growth is 5 μm or more and 50 μm or less in the first embodiment of the present invention. Only the gallium nitride based semiconductor laser device according to the example is used.
When the thickness of the substrate is smaller than 5 μm, the mechanical strength of the substrate is reduced, so that the substrate is easily broken, and the substrate is broken when handling the wafer, which leads to an increase in cost.

In the present embodiment, the number of the quantum well layers 14 constituting the multi-quantum well structure active layer 6 is two. However, a multi-quantum well structure having three or more layers may be used. A single quantum well structure may be used. Further, in the present embodiment, the layer thicknesses of the quantum well layer 14 and the barrier layer 15 are both 5 nm, but these layer thicknesses need not be the same, and may be different. Further, the thickness of the quantum well layer is not limited to this embodiment.

In this embodiment, the Al _0.2 Ga _0.8 N evaporation preventing layer 7 is formed so as to be in contact with the active layer 6 having a multiple quantum well structure. However, the growth temperature of the quantum well layer 14 is increased. This is to prevent evaporation in between. Therefore, any material that protects the quantum well layer 14 can be used as the evaporation prevention layer 7 and has another Al composition.
You may use 1GaN ternary mixed crystal or GaN. The evaporation preventing layer 7 may be doped with Mg. In this case, there is an advantage that holes are easily injected from the p-GaN guide layer 8 and the p-Al _0.1 Ga _0.9 Np type clad layer 9. Further, when the In composition of the quantum well layer 14 is small, the quantum well layer 14 does not evaporate even if the evaporation prevention layer 7 is not formed. The characteristics of the system semiconductor laser device are not impaired.

In this embodiment, the injection current is narrowed by forming the ridge stripe structure. However, other current narrowing methods such as an electrode stripe structure may be used. Further, in the present embodiment, the cavity facet of the laser is formed by cleavage, but the cavity facet can also be formed by dry etching.

Further, in this embodiment, since the semi-insulating GaN substrate is used, the n-side electrode 12 is formed on the surface of the n-GaN n-type contact layer 3 exposed by etching. , The n-side electrode 12 may be formed on the back surface of the substrate. Further, the p-type and n-type configurations may be reversed.

When the gallium nitride based semiconductor laser of this embodiment was used as a light source for reading data from an optical disk, return light from the optical disk which was incident on the laser emission surface at a distance of about 60 μm from a light emitting portion was generated. , GaN
It was not incident on the substrate. Therefore, in the conventional example in which a substrate thicker than 50 μm was used, this return light incident on the substrate caused noise of the semiconductor laser and caused a data read error, but in this embodiment, the substrate was as thin as 50 μm or less. As a result, the return light does not enter the substrate, the generation of noise due to the return light is suppressed, and the effect that no data reading error occurs is obtained.

(Embodiment 2) FIG. 4 is a sectional view showing a gallium nitride based semiconductor light emitting diode device according to a second embodiment of the present invention. In this figure, 21 is an n-type GaN substrate having a c-plane as a surface and having a thickness of 20 μm and a diameter of 2 inches, 22 is an n-GaN n-type contact layer, and 23 is an n-Al _0.1 Ga _0.9 Nn-type clad layer. , 24
Is an n-GaN guide layer, 25 is an active layer having a single quantum well structure composed of an In _0.2 Ga _0.8 N quantum well layer, and 26 is an Al _0.2
Ga _0.8 N evaporation preventing layer, 27 is a p-GaN guide layer, 2
8 p-Al _0.1 Ga _0.9 Np-type cladding layer, the 29 p-
A GaN p-type contact layer, 30 is a p-side electrode, and 31 is an n-side electrode.

In this embodiment, the thickness of the n-type GaN substrate 21 is set to 20 μm, but the thickness is not limited as long as it is between 5 μm and 50 μm. The surface of the substrate may have another plane orientation such as the a-plane.

N-type cladding layer 23 and p-type cladding layer 2
8 is Al having an Al composition other than n-Al _0.1 Ga _0.9 N.
A GaN ternary mixed crystal or simply GaN may be used. In this case, when the Al composition is increased, the energy gap difference between the active layer and the cladding layer increases, and the carriers are effectively confined in the active layer, thereby improving the temperature characteristics. Further, when the Al composition is reduced to such an extent that the confinement of the carriers is maintained, the mobility of the carriers in the cladding layer is increased, so that there is an advantage that the element resistance of the light emitting diode element can be reduced. Further, these cladding layers may be quaternary or higher mixed crystal semiconductors containing trace amounts of other elements, and the composition of the mixed crystal in the n-type cladding layer 23 and the p-type cladding layer 28 may not be the same.

The guide layers 24 and 27 are made of a material whose energy gap has a value between the energy gap of the quantum well layer constituting the single quantum well structure active layer 25 and the energy gap of the cladding layers 23 and 28. If GaN is not limited to other materials, such as InGaN / Al
GaN ternary mixed crystal, InGaAlN quaternary mixed crystal, or the like may be used. Further, it is not necessary to dope the entire guide layer with a donor or an acceptor, and only a part of the single quantum well structure active layer 25 side may be non-doped, and further, the entire guide layer may be non-doped. In this case, there is an advantage that the number of carriers existing in the guide layer is reduced, light absorption by free carriers is reduced, and light output is further improved. The guide layers 24 and 27 have an advantage that electrons and holes can be easily injected from the n-type cladding layer 23 and the p-type cladding layer 28 into the single quantum well structure active layer 25, respectively. 24 and 2
Even if the layer 7 is not provided, the LED element characteristics will not be significantly deteriorated, so that the guide layers 24 and 27 may be omitted.

I constituting the single quantum well structure active layer 25
The composition of the n _0.2 Ga _0.8 N quantum well layer may be set according to the required emission wavelength. If the emission wavelength is to be increased, the In composition of the quantum well layer 25 is to be increased, and if the emission wavelength is to be shortened, the quantum well layer is to be reduced. 25 In composition is reduced. Further, the quantum well layer 25 may be a quaternary or higher mixed crystal semiconductor containing a small amount of another element in the ternary mixed crystal of InGaN.

Next, a method for fabricating the gallium nitride based semiconductor light emitting diode will be described with reference to FIG. In the following description, the case where MOCVD (metal organic chemical vapor deposition) is used is shown, but any growth method capable of epitaxially growing GaN may be used, such as MBE (molecular beam epitaxy) or HDVPE (hydride vapor phase epitaxy). Other vapor phase epitaxy methods such as the method described above.

First, on an n-type GaN substrate 21 having a c-plane as a surface and a thickness of 20 μm and a diameter of 2 inches, which is set on a heating element in a predetermined growth furnace, TMG, NH ₃ ,
Using SiH ₄ as a raw material and a growth temperature of 1050 ° C., a 3 μm-thick Si-doped n-GaN n-type contact layer 22 is grown. Subsequently, TMA was added to the raw material, and 0.3 μm thick S
An i-doped n-Al _0.1 Ga _0.9 Nn-type clad layer 23 is grown. Then, excluding TMA from the raw material, the growth temperature was kept at 1050 ° C., and the Si-doped n-
A GaN guide layer 24 is grown.

Next, the growth temperature was lowered to 800 ° C.
, NH ₃ , and TMI as raw materials, and a 3 nm-thick I
An active layer 25 having a single quantum well structure composed of an n _0.2 Ga _0.8 N quantum well layer is formed. Continue with TMG, TMA and N
Using H ₃ as a raw material, an Al _0.2 Ga _0.8 N evaporation preventing layer 26 having a thickness of 10 nm is grown at a growth temperature of 800 ° C.

Next, the growth temperature is increased again to 1050 ° C., and a 0.05 μm-thick Mg-doped p-GaN guide layer 27 is grown using TMG, NH ₃ and Cp ₂ Mg as raw materials. Subsequently, TMA was added to the raw material, and the growth temperature was kept at 1050 ° C., and a 0.3 μm-thick Mg-doped p-
An Al _0.1 Ga _0.9 Np type clad layer 28 is grown. Subsequently, the TMA is removed from the raw material, and the Mg-doped p-GaN p-type contact layer 29 having a thickness of 0.2 μm is grown at a growth temperature of 1050 ° C. to complete a gallium nitride based epitaxial wafer.

Thereafter, the wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to lower the resistance of the Mg-doped p-type layer.

Subsequently, the p-GaN p-type contact layer 29
A p-side electrode 30 made of nickel and gold is formed on the surface of
An n-side electrode 31 made of titanium and aluminum is formed on the back surface of the n-type GaN substrate 21 to complete a gallium nitride-based LED wafer.

Thereafter, the wafer is divided into individual chips. Then, each chip is mounted on the stem, the n-side electrode 31 and the stem are connected, and the p-side electrode 30 and the lead terminal are connected by wire bonding, thereby completing a gallium nitride based semiconductor light emitting diode device.

The blue LED device manufactured as described above exhibited light emission characteristics of a light emission wavelength of 430 nm and a light output of 4 mW at a forward current of 20 mA. Example 1
Similarly to the above, the distribution of the emission wavelength in the surface of the substrate wafer becomes smaller, and the center of the wafer and the peripheral portion are conventionally 150 nm.
The difference in the emission wavelength was reduced to 3 nm. As described above, according to the present invention, the distribution of the light emission characteristics from the InGaN quantum well active layer is improved, and a gallium nitride based semiconductor light emitting diode element having a uniform light emission wavelength within the surface of the substrate wafer can be realized.

In this embodiment, the number of In _0.2 Ga _0.8 N quantum well layers constituting the single quantum well structure active layer 25 is set to 1 and the thickness is set to 3 nm. A structure active layer may be used, and the layer thickness of the quantum well layer is not limited to this embodiment.

In this embodiment, the Al _0.2 Ga _0.8 N evaporation preventing layer 26 is in contact with the single quantum well structure active layer 25.
Is formed in order to prevent the quantum well layer 25 from evaporating while the growth temperature is being increased. Therefore, any material that protects the quantum well layer 25 can be used as the evaporation prevention layer 26, and an AlGaN ternary mixed crystal or GaN having another Al composition may be used. The evaporation preventing layer 26 may be doped with Mg. In this case, the p-GaN guide layer 27 or the p-Al _0.1
There is an advantage that holes are easily injected from the Ga _0.9 Np type cladding layer 28. Further, In of the quantum well layer 25
When the composition is small, the quantum well layer 25 does not evaporate without forming the evaporation prevention layer 26. Therefore, even if the evaporation prevention layer 26 is not formed, the characteristics of the gallium nitride based semiconductor light emitting diode element of the present embodiment are It is not spoiled.

Further, in this embodiment, since the n-type GaN substrate is used, a dry etching step for exposing the n-GaN n-type contact layer as in the first embodiment is not required, so that the cost in manufacturing the blue LED is reduced. Can be reduced. Note that the p-type and n-type configurations may be reversed. When a semi-insulating GaN substrate is used, it can be manufactured by the same manufacturing process as the conventional one. However, if the thickness of the substrate at the time of crystal growth is 5 μm or more and 50 μm or less, the present invention similar to the second embodiment can be obtained. The effect is obtained.

(Embodiment 3) FIG. 5 is a sectional view showing a gallium nitride based semiconductor laser device according to a third embodiment of the present invention, and FIG. 6 is an enlarged sectional view of a portion B in FIG. FIG. In this figure, reference numeral 41 denotes an n-type GaN substrate having a c-plane as a surface, a thickness of 8 μm, and a diameter of 2 inches;
42 is an n-GaN buffer layer, 43 is an n-GaN layer, 4
4 n-Al _0.1 Ga _0.9 Nn-type cladding layer, the 45 n-
A GaN guide layer, 46 is a multiple quantum well structure active layer comprising three In _0.2 Ga _0.8 N quantum well layers 54 and two In _0.05 Ga _0.95 N barrier layers 55, and 47 is Al _0.2 Ga _0.8 N
Evaporation prevention layer, 48 is a p-GaN guide layer, 49 is pA
l _0.1 Ga _0.9 Np type cladding layer, 50 is a p-GaN p type contact layer, 51 is a p-side electrode, 52 is an n-side electrode, 53
Is an SiO ₂ insulating film.

In this embodiment, the thickness of the n-type GaN substrate 41 is set to 8 μm. However, the thickness is not limited as long as it is between 5 μm and 50 μm. The surface of the substrate may have another plane orientation such as the a-plane.

The n-GaN buffer layer 42 is made of n-type GaN
This is to prevent the crystallinity of the gallium nitride based semiconductor light emitting portion formed thereon from being deteriorated due to the deterioration of the surface state of the substrate 41. However, if the surface state of the n-type GaN substrate 41 is kept good. As long as the buffer layer 42 is not provided. The material of the buffer layer 42 is not limited to GaN as long as a gallium nitride-based semiconductor can be epitaxially grown thereon.
Although a ternary mixed crystal of AlGaN or the like may be used, it is preferable to use GaN from the viewpoint of reducing a potential barrier due to a heterojunction. Further, the n-type cladding layer 44, the p-type cladding layer 49, and the guide layers 45 and 48 may use other compositions or other materials without being limited to the present embodiment, as in the first embodiment.

Next, a method for fabricating the gallium nitride based semiconductor laser will be described with reference to FIGS. In the following description, the case where MOCVD (metal organic chemical vapor deposition) is used is shown, but any growth method capable of epitaxially growing GaN may be used, such as MBE (molecular beam epitaxy) or HDVPE (hydride vapor phase epitaxy). Other vapor phase epitaxy methods such as the method described above.

First, TMG and NH ₃ were placed on an n-type GaN substrate 41 having a c-plane as a surface and having a thickness of 8 μm and a diameter of 2 inches, which was placed on a heating element in a predetermined growth furnace. The n-GaN buffer layer 42 is grown to 35 nm at a growth temperature of 600 ° C.

Next, the growth temperature is raised to 1050 ° C., and a 1 μm-thick Si-doped n-GaN layer 43 is grown using TMG, NH ₃ and SiH ₄ as raw materials. Subsequently, TMA was added to the raw material, and the Si-doped n-Al _0.1 Ga _0.9 layer having a thickness of 0.7 μm was kept at a growth temperature of 1050 ° C.
A Nn-type cladding layer 44 is grown. Subsequently, the TMA was removed from the raw material, and the growth temperature was kept at 1050 ° C. and the thickness was reduced to 0.1 mm.
A 05 μm Si-doped n-GaN guide layer 45 is grown.

Next, the growth temperature was lowered to 800 ° C.
, NH ₃ , and TMI as raw materials, and In _0.2 Ga _0.8
N quantum well layer (4 nm thick) 54 and In _0.05 Ga _0.95 N
Barrier layers (thickness: 3 nm) 55 are alternately grown two by two, and one In _0.2 Ga _0.8 N quantum well layer (thickness: 4 nm) 54 is finally grown to form a multiple quantum well structure active layer (total thickness). (18 nm) 46 is created. Continue to T
Using MG, TMA and NH ₃ as raw materials, the growth temperature is 80
At 0 ° C., an Al _0.2 Ga _0.8 N evaporation preventing layer 47 having a thickness of 10 nm is grown.

Next, the growth temperature is raised to 1050 ° C. again, and a Mg-doped p-GaN guide layer 48 having a thickness of 0.05 μm is grown using TMG, NH ₃ and Cp ₂ Mg as raw materials. Subsequently, TMA was added to the raw material, and the growth temperature was kept at 1050 ° C., and the Mg-doped p-
An Al _0.1 Ga _0.9 Np type clad layer 49 is grown. Subsequently, the Mg-doped p-GaN p-type contact layer 50 having a thickness of 0.2 μm is grown at a growth temperature of 1050 ° C., excluding TMA from the raw material, to complete a gallium nitride-based epitaxial wafer.

Thereafter, the wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to lower the resistance of the Mg-doped p-type layer. Further, the p-GaN p-type contact layer 50 and p-type p-GaN p-type contact layer 50 are formed on the outermost surface of the p-GaN p-type contact layer 50 by using ordinary photolithography and dry etching techniques so as to form a ridge structure having a stripe shape of 5 μm width.
-The Al _0.1 Ga _0.9 Np type clad layer 49 is etched.

Subsequently, a 200 nm thick SiO ₂ insulating film 53 is formed on the side surfaces of the ridge and on the surface of the p-type layer other than the ridge. A p-side electrode 51 made of nickel and gold is formed on the surface of the SiO ₂ insulating film 53 and the p-GaN p-type contact layer 50, and an n-side electrode 52 made of titanium and aluminum is formed on the back surface of the n-type GaN substrate 41. Thus, a gallium nitride based LD wafer is completed.

Thereafter, the wafer is cleaved in a direction perpendicular to the ridge stripe to form a laser cavity end face.
It is further divided into individual chips. Then, each chip is mounted on a stem, the n-side electrode 52 and the stem are connected,
The gallium nitride based semiconductor laser device is completed by connecting the p-side electrode 51 and the lead terminal by wire bonding.

The blue LD device manufactured as described above had laser characteristics of an oscillation wavelength of 430 nm and an oscillation threshold current of 40 mA. In addition, the distribution of the oscillation wavelength in the plane of the substrate wafer became smaller, and the difference in the oscillation wavelength between the center and the periphery of the wafer, which was conventionally 150 nm, was reduced to 5 nm. As described above, also in this embodiment, InGa
The distribution of the emission characteristics from the N quantum well active layer was improved, and a gallium nitride based semiconductor laser device having a uniform oscillation wavelength and a low oscillation threshold current value within the surface of the substrate wafer was realized.

In the present embodiment, the thickness of the n-type GaN substrate is reduced to 8 μm, so that when the reflection end face of the laser resonator is formed by cleavage, the cleavage is easily performed. As a result, the production yield of the device was improved and the cost was reduced. Furthermore, since the n-side electrode was formed on the back surface of the substrate using the n-type GaN substrate, only one wire bonding process was required, and the device manufacturing process was simplified.

In this embodiment, the n-type GaN substrate is used. However, the configuration of the p-type and n-type may be reversed by using a GaN substrate having p-type conductivity. Further, in the present embodiment, the number of the quantum well layers 54 constituting the multiple quantum well structure active layer 46 is three, but a multiple quantum well structure of two layers or four or more layers may be used. A single quantum well structure may be used. Further, the thicknesses of the quantum well layer and the barrier layer are not limited to the present embodiment, and other thicknesses can be used.

[0068]

As described above, the gallium nitride based semiconductor light emitting device according to the present invention contains at least indium and gallium sandwiched between a cladding layer and / or a guide layer made of a nitride semiconductor by a vapor growth method. By reducing the thickness of the substrate when forming the quantum well structure active layer made of a nitride semiconductor to 5 μm or more and 50 μm or less, the temperature difference between the bottom surface and the surface of the substrate when growing InGaN crystal is eliminated. By suppressing the warpage of the substrate wafer during the growth of the base crystal, the substrate wafer comes into contact with the heating element on the entire bottom surface, so that the distribution of the surface temperature in the substrate wafer surface was suppressed.

Further, by using gallium nitride as the substrate, the difference in the coefficient of thermal expansion between the semiconductor layer formed on the substrate and the substrate is reduced, and the warpage of the wafer due to thermal distortion is suppressed, so that the in-plane of the substrate wafer can be reduced. The distribution of surface temperature was further improved.

As a result, the distribution of the light emission characteristics from the InGaN quantum well active layer is improved, the gallium nitride based semiconductor laser device having a uniform oscillation wavelength and a low oscillation threshold current value within the substrate wafer surface, and A gallium nitride-based light emitting diode device having a uniform emission wavelength was realized.

When the gallium nitride based semiconductor laser of this embodiment was used as a light source for reading data from an optical disk, no return light was incident on the substrate because the substrate was as thin as 50 μm or less. The occurrence was suppressed, and the data read error was reduced. Furthermore, when the reflection end face of the laser resonator is formed by cleavage due to the thinness of the substrate, cleavage can be performed with good yield, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a portion A of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 shows the dependence of the difference in oscillation wavelength between the central part and the peripheral part of the wafer on the thickness of the GaN substrate in the gallium nitride based semiconductor laser device and the G of the oscillation threshold current value.
FIG. 4 is a graph showing the thickness dependency of an aN substrate.

FIG. 4 is a sectional view showing a semiconductor light emitting diode device according to a second embodiment of the present invention.

FIG. 5 is a sectional view showing a semiconductor laser device according to a third embodiment of the present invention.

FIG. 6 is an enlarged sectional view of a portion B of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 7 shows a conventional blue LD using a gallium nitride based semiconductor.
FIG.

FIG. 8 shows a conventional blue LE using a gallium nitride-based semiconductor.
It is sectional drawing of D.

FIG. 9 is a diagram showing the warpage of a substrate when the temperature of a conventional substrate wafer placed on a heating element is increased.

[Explanation of symbols]

1 semi-insulating GaN substrate 2 non-doped GaN buffer layer 3 n-Gann type contact layer 4 n-Al _0.1 Ga _0.9 Nn type cladding layer 5 n-GaN guide layer 6 multiple quantum well structure active layer 7 Al _0.2 Ga _0.8 N evaporation preventing Layer 8 p-GaN guide layer 9 p-Al _0.1 Ga _0.9 Np-type cladding layer 10 p-GaN p-type contact layer 12 n-side electrode 13 SiO ₂ insulating film 14 In _0.2 Ga _0.8 N quantum well layer 15 In _0.05 Ga _0.95 N barrier layer

Claims (2)

[Claims] 1. A nitride for forming a quantum well structure active layer made of a nitride semiconductor containing at least indium and gallium sandwiched between a clad layer and / or a guide layer made of a nitride semiconductor by a vapor growth method. A method for manufacturing a gallium nitride-based semiconductor light emitting device, wherein a thickness of a gallium substrate is 5 μm or more and 50 μm or less. 2. A substrate for forming a quantum well structure active layer made of a nitride semiconductor containing at least indium and gallium sandwiched between a clad layer and / or a guide layer made of a nitride semiconductor by a vapor phase growth method. A gallium nitride based semiconductor light emitting device having at least one quantum well layer obtained by setting the thickness of the semiconductor layer to 5 μm or more and 50 μm or less.