JPH08264899A - Manufacture of gallium nitride semiconductor - Google Patents

Abstract

PURPOSE: To provide a vapor growth method of a high-quality single-crystal GaN layer. CONSTITUTION: GaN buffer layer 2 is deposited on a sapphire substrate 1 by metal organic vapor-phase epitaxy(MOVPE) at 600 deg.C by supplying trimethylgallium(TMG) and ammonium with hydrogen as a carrier gas. Then, the supply of TMG is stopped, temperature is increased to 1030 deg.C within the mixed atmosphere of ammonium and hydrogen, and further single-crystal GaN layer 3 is deposited by adding triethylgallium(TEG). Therefore, by switching a feed gas, a flat GaN buffer layer with less residual impurity can be deposited over a wide temperature range, the mixture of such impurity as carbon can be suppressed in the growth of the single-crystal GaN layer, and a GaN single crystal with an improved C-axis orientation property and a high crystallizability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a gallium nitride-based semiconductor used for a light emitting diode in a wavelength range from blue to ultraviolet or a semiconductor laser diode in the same wavelength range, and particularly to electrical, optical and crystalline structure. The present invention relates to a vapor phase growth method of a gallium nitride-based semiconductor having excellent properties.

[0002]

2. Description of the Related Art A blue light emitting device is expected as a light source for a full color display or an optical disk capable of high density recording, and is a II-VI group compound semiconductor such as ZnSe or III such as SiC or GaN.
-A lot of research is being done using group V compound semiconductors.
In particular, a blue light emitting diode has recently been realized using GaN, GaInN, etc., and a light emitting element using a gallium nitride-based semiconductor has attracted attention. Metalorganic vapor phase epitaxy (MOVPE method) and molecular beam epitaxy method (MBE method) are generally used as a method for depositing a gallium nitride based semiconductor crystal.

For example, a deposition method using the MOVPE method will be described. Organometallic trimethylgallium (TMG) and ammonia (NH3) are placed in a reactor equipped with a sapphire substrate.
Is used as a carrier gas for hydrogen at 600 ° C.
After depositing a polycrystalline GaN buffer layer at a temperature of about 100 ° C., the supply of TMG, which is a Ga raw material, is stopped and the substrate is cooled to 100
The temperature is raised to about 0 ° C. Next, TMG is again supplied onto the substrate to deposit a GaN single crystal layer.

Other than the Ga raw material, there is triethylgallium (TEG), etc., but in any case, the Ga raw material is the same in vapor phase growth of the GaN buffer layer and the GaN single crystal layer. is there.

[0005]

However, in vapor phase growth such as the conventional method, the electrical, optical, and
Not all crystallographic properties can be of high quality.
For example, a GaN single crystal used for a blue light emitting diode using TMG as a Ga raw material has an excellent crystal structure, but has a level in the forbidden band due to residual impurities and defects. It makes the realization of semiconductor lasers impossible.

Further, when TEG is used as a Ga raw material, an excellent GaN single crystal can be produced in terms of crystal structure, but it is necessary to deposit a GaN buffer layer at a considerably low temperature in order to suppress surface irregularities. As a result, a large amount of impurities and defects are present in the buffer layer, which deteriorates the optical properties of the GaN single crystal layer on it. When the deposition temperature of the GaN buffer layer is increased to suppress the inclusion of impurities in the crystal, GaN
However, because of the large lattice mismatch between the substrate and the GaN crystal on the sapphire substrate, the surface irregularities become large and the device structure of the light emitting device cannot be deposited.

An object of the present invention is to solve the above problems and provide a method for producing a gallium nitride-based semiconductor excellent in electrical, optical and crystal structure.

[0008]

Means for solving the problems Means for solving the above problems are as follows.

The first means is MO of gallium nitride based semiconductor.
A step of depositing a GaN low temperature deposition layer on the substrate at 500 ° C. or higher and 600 ° C. or lower using trimethylgallium on the substrate in VPE vapor phase growth, and using triethylgallium on the GaN low temperature deposition layer at a temperature higher than the deposition temperature to form a GaN single crystal A method for manufacturing a gallium nitride-based semiconductor, comprising the step of depositing a layer. In particular, the gallium nitride-based semiconductor manufacturing method is effective when a sapphire C surface is used as the substrate.

The second means is to use trimethylgallium on the substrate in vapor phase growth of gallium nitride-based semiconductors.
N a step of depositing a low temperature deposition layer, a step of heat treating the substrate on which the GaN low temperature deposition layer is deposited at a temperature above the deposition temperature for a certain time in a mixed gas atmosphere of ammonia and hydrogen, and using triethylgallium after the heat treatment And a step of depositing a GaN single crystal layer at the deposition temperature or higher.
Particularly, the heat treatment is a method for producing a gallium nitride-based semiconductor in which it is effective to perform the heat treatment at 1000 ° C. or higher within 1 hour.

[0011]

According to the first method for manufacturing a gallium nitride-based semiconductor of the present invention, when the GaN buffer layer is deposited using TMG, the polycrystalline GaN buffer layer can be deposited at a high temperature. A small number of buffer layers can be formed.
When TEG is used as the source gas, the buffer layer becomes a single crystal instead of a polycrystal at a high temperature, so this layer is not suitable for the buffer layer. Is it a single crystal here,
Whether it becomes polycrystalline depends on the decomposition temperature of the raw material gas.
That is, if it is deposited at a temperature higher than the decomposition temperature of the source gas, it becomes a single crystal, and if it is deposited at a lower temperature, it becomes a polycrystal. In the present invention, since the TEG gas having a high decomposition temperature is used, the deposition temperature itself lower than the decomposition temperature can be set to a relatively high temperature, so that the buffer layer can be deposited at a high temperature and in a polycrystalline state. By depositing at a high temperature, mixing of impurities can be reduced. Further, since the buffer layer is polycrystalline, the surface irregularities are small and can be made flat.

In summary, when a GaN buffer layer is deposited using TMG, the decomposition temperature of TMG is higher than the decomposition temperature of TEG by about 100 ° C., so the surface unevenness is small and remains over a wide temperature range. It is possible to deposit a polycrystalline GaN buffer layer containing less impurities, particularly oxygen, which has a large effect on crystallinity. The reason why the decomposition temperature of TMG is about 100 ° C. higher than that of TEG is that, as shown in FIGS. 2 (a) and 2 (b), in the TMG of (a), the molecule directly bonded to Ga is a methyl group, and T shown in b)
It is considered that the binding energy is large because the mass is smaller than the ethyl group in EG.

Further, when GaN single crystal is grown on the buffer layer, by switching to TEG as a Ga raw material, carbon mixing of residual impurities, which is excellent in C-axis orientation and contributes to a deep level, is suppressed. .

According to the second method for producing a gallium nitride-based semiconductor of the present invention described above, even if a GaN buffer layer in a polycrystalline state having particularly poor crystallinity is deposited at a low temperature of 500 ° C. or lower, the GaN single layer on the buffer layer is deposited. If heat treatment is performed at a temperature of 1000 ° C. or higher in a mixed atmosphere of ammonia and hydrogen before crystal growth, the buffer layer can be made to be a single crystal to some extent.
By depositing a single crystal, a GaN single crystal with good crystallinity can be obtained. The heat treatment is preferably carried out for less than 1 hour, and if it is carried out for more than 1 hour, surface irregularities increase and the opposite effect is obtained.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 First, as shown in FIG. 1, a GaN buffer layer 2 is deposited on a C-face 1 of a sapphire substrate by using trimethylgallium (TMG). Crystal growth is performed by metal organic vapor phase epitaxy (MOVPE).

Prior to vapor phase growth, the sapphire substrate 1 is placed on a susceptor in a reaction furnace, evacuated and then heated at 1100 ° C. for 15 minutes in a hydrogen atmosphere of 70 Torr to clean the substrate surface.

Next, after cooling to 600 ° C., TMG was added to 60
μmol / min, 2.5 L / min of ammonia and 2 L / min of carrier hydrogen are flown to deposit the GaN buffer layer 2 to a thickness of 50 nm.

Then, only the TMG supply is stopped and the temperature is adjusted to 10
After heating up to 30 ℃, supply TEG at 60μmol / min
An aN single crystal layer 3 is deposited to 1.2 μm. Then, only the TEG supply is stopped, and the mixture is cooled to room temperature in a mixed atmosphere of ammonia and hydrogen.

The above temperature profile and gas supply profile are as shown in FIG. 3, but the source gas is TMG.
The feature is to switch from TEG to TEG. .

Next, the effectiveness of depositing the GaN buffer layer 2 using TMG will be described. FIG. 4 shows the growth temperature dependence of surface roughness (irregularities) when a GaN low temperature deposition layer, that is, a buffer layer is grown on a sapphire substrate by the MOVPE method.

According to the experiment, when TMG is used as the source gas, the surface is flat at 600 ° C. or less and the roughness is small, but when TEG is used, the temperature is 500 ° C., which is lower than when TMG is used.
Only a flat surface could be obtained. The increase in roughness at high temperature is considered to be due to the initiation of nucleation of GaN single crystals on a sapphire substrate with a large lattice mismatch.
A flat GaN single crystal cannot be deposited on the buffer layer.

Also, at 500 ° C. or lower, almost no GaN was deposited in any of the raw materials. Therefore, when TEG is used as the raw material for the GaN buffer layer, the growth temperature is 5
The quality of the GaN single crystal layer is fluctuated by a slight change in the condition, which is limited to around 00 ° C.

On the other hand, when TMG is used for depositing the buffer layer, as can be seen from FIG. 4, a flat surface can be obtained over a temperature range of about 100 ° C., and deposition can be performed under a wide growth condition. Furthermore, its deposition temperature can be realized at a higher temperature than that when TEG is used. The higher the growth temperature, the more advantageous is the suppression of incorporation of residual impurities. This will be described with reference to FIG.

FIG. 5 shows GaN using TMG on a sapphire substrate.
5 shows a depth profile obtained by SIMS analysis of residual impurities in a sample in which a buffer layer (low temperature deposition layer, 600 ° C.) and a GaN single crystal layer (high temperature deposition layer, 1030 ° C.) were deposited. The low temperature deposition layer contains a considerable amount of carbon, oxygen and hydrogen,
In the layer with high growth temperature, these were almost at the detection limit. In particular, oxygen slightly diffuses into the GaN single crystal layer and causes defects that create deep levels, so it is necessary to suppress this.

However, when TEG is used as the material of the buffer layer, the growth temperature of the buffer layer needs to be further lowered by 100 ° C., and the mixing and diffusion of impurities become more serious.
Therefore, it is found that using TMG as the raw material of the GaN buffer layer is more effective from the viewpoint of mixing impurities.

Next, the effectiveness of using TEG as a raw material for the GaN single crystal layer on the GaN buffer layer will be described.

First, in terms of impurity mixing, from the result of the SIMS profile of FIG. 5 described above, no impurities exceeding the detection limit were detected in the GaN single crystal layer deposited by using TEG. However, in the GaN single crystal layer deposited using TMG, about 1.5 times the carbon level in the GaN single crystal layer deposited using TEG was detected. When the electrical characteristics of the samples using TMG or TEG as the raw material of the GaN single crystal layer were examined by Hall measurement, all the samples had high resistance.

However, when photoluminescence is measured at a low temperature, the emission from the deep level is dominant from the GaN single crystal using TMG as shown in FIG.
A large band edge emission was observed from the GaN single crystal using.

Further, FIG. 7 shows the result of examining the GaN single crystal film thickness dependence of the full width at half maximum of the diffraction peak of the (0002) plane using X-ray diffraction. It was found that the present invention using TEG for the GaN single crystal layer has a narrower full width at half maximum of the diffraction peak and is superior in C-axis orientation than the conventional method using TMG.

As described above, the source gas for the buffer layer is made to contain T
By using MG and TEG as a raw material for the single crystal layer,
A good GaN single crystal layer was obtained. The table below shows the summary.

[0032]

[Table 1]

Although the sapphire C plane is used as the substrate in this embodiment, it is clear that the plane orientation may be any direction. Furthermore, the substrate is not limited to sapphire,
Needless to say, a similar effect can be obtained with a substrate such as SiC.

Example 2 A second deposition method of the GaN crystal laminated structure shown in FIG. 1 will be described. As shown in the temperature profile and gas supply profile of FIG.
Prior to MOVPE vapor phase growth, the sapphire substrate 1 is placed on a susceptor in a reaction furnace, vacuum exhausted, and then heated at 1100 ° C. for 15 minutes in a hydrogen atmosphere of 70 Torr to clean the substrate surface. Then, after cooling to 500 ° C. or 600 ° C., 60 μmol / min of TMG and 2.
5 L / min and 2 L / min of carrier hydrogen are flown to deposit the GaN buffer layer 2 to 50 nm. Next, only the supply of TMG is stopped, the temperature is raised to 1030 ° C., and this state is maintained for 1 hour for heat treatment. Next, supply TEG at 60 μmol / min to obtain GaN.
The single crystal layer 3 is deposited to 1.2 μm. Then, only the TEG supply is stopped, and the mixture is cooled to room temperature in a mixed atmosphere of ammonia and hydrogen.

In order to investigate the effect of the heat treatment, the surface roughness of the GaN buffer layer deposited at 500 ° C. and 600 ° C. with respect to the heat treatment time and the full width at half maximum of the X-ray diffraction peak of the (0002) plane are shown in FIG. Is. 500 ° C
It was found that the roughness of the polycrystalline layer having a strong polycrystalline state deposited in step 3 increased for 30 minutes or more, and gradually became a single crystal. At this time, it was found that the full width at half maximum of the X-ray diffraction peak of the GaN single crystal layer on the buffer layer subjected to this heat treatment was narrowed corresponding to the single crystallization of the buffer layer, and the crystallinity was improved.

On the other hand, the roughness of the buffer layer deposited at 600 ° C. hardly changes even when heat treatment is applied, and is a thermally stable buffer layer which is considerably close to a single crystal state. At this time, the full width at half maximum of the X-ray diffraction peak of the GaN single crystal layer on the buffer layer subjected to this heat treatment hardly changes. From the results of the above heat treatment, there are polycrystalline GaN buffer layers with various degrees of single crystallization in the temperature range between 500 ° C and 600 ° C, which is ideal for relaxing strain with a substrate with a large lattice mismatch. It was found that various polycrystalline states existed.

From the above results, the GaN buffer layer was deposited in the temperature range between 500 ° C. and 600 ° C., and the heat treatment was applied. After the deposition at 540 ° C., the heat treatment was applied at 1030 ° C. for 15 minutes. The full width at half maximum of the X-ray diffraction peak of the upper GaN single crystal layer was 90 seconds, the highest value not previously reported, and high-quality GaN single crystal with high resistance and very strong band edge emission was obtained. Was given.

From the experimental results of this time, it is preferable that the heat treatment is 1000 ° C. or higher, and if the temperature is lower than this temperature, the heat treatment takes too long and the crystallinity is lowered. The heat treatment time is preferably within 1 hour in order to avoid deterioration of crystallinity.

Although the sapphire C plane is used as the substrate in this embodiment, it is obvious that the plane orientation may be any direction. Furthermore, the substrate is not limited to sapphire,
Needless to say, a similar effect can be obtained with a substrate such as SiC.

Further, the heat treatment atmosphere is not limited to a mixed atmosphere of ammonia and hydrogen, but an atmosphere capable of suppressing dissociation of nitrogen atoms from the GaN single crystal surface, that is, an atmosphere containing nitrogen atoms such as nitrogen gas has the same effect. can get.

In this embodiment, the source gas for the buffer layer is T
Although MG is used, TEG gas may be used as a raw material because heat treatment is performed after the buffer layer is deposited.

Example 3 A semiconductor laser is manufactured by growing a crystal on the GaN single crystal produced in Example 1 or Example 2.

First, the GaN single crystal 3 shown in FIG. 1 has a low impurity concentration, a flat surface, and an excellent C-axis orientation. Therefore, the crystal 3 is suitable for a semiconductor laser. Can grow crystals.

In this embodiment, an InGaN layer is formed as an active layer on the single crystal 3, and GaN is formed as a barrier layer on both sides of the active layer.
A double hetero structure semiconductor laser provided with a barrier layer is constituted. In this laser, as described above, the buffer layer on the substrate side and the GaN single crystal layer 3 have a structure suitable for the subsequent crystal.

[0045]

As described above, according to the first manufacturing method of the present invention, a buffer layer having a flat surface can be deposited over a wide temperature range. Residual impurities can be suppressed, and diffusion and mixing of impurities into the GaN single crystal on the buffer layer can be suppressed. Further GaN
Even in the growth of the single crystal itself, it is possible to suppress the mixing of impurities and to realize a GaN single crystal layer having a good C-axis orientation.

According to the second manufacturing method of the present invention, it is possible to realize the optimum polycrystalline state of the GaN buffer layer for relaxing the strain generated between the substrate and the substrate having a large lattice mismatch. A high quality GaN single crystal layer having an ideal C-axis orientation is realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross section of an experimental sample.

FIG. 2 shows the molecular structures of trimethylgallium (TMG) and triethylgallium (TEG).

FIG. 3 is a diagram showing a temperature profile and a gas supply profile according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the growth temperature dependence of surface roughness (irregularities) when a GaN low temperature deposition layer, that is, a buffer layer is grown on a sapphire substrate by the MOVPE method.

FIG. 5 SIMS of residual impurities in a sample obtained by depositing a GaN buffer layer (low temperature deposition layer, 600 ° C.) and a GaN single crystal layer (high temperature deposition layer, 1030 ° C.) on a sapphire substrate using TMG.
Diagram showing analysis results

FIG. 6 shows low temperature (16K) photoluminescence of GaN single crystals deposited using TMG or TEG.

FIG. 7 is a diagram showing the GaN single crystal film thickness dependence of the full width at half maximum of the diffraction peak of the (0002) plane observed using X-ray diffraction.

FIG. 8 is a diagram showing a temperature profile and a gas supply profile according to Example 2 of the present invention.

FIG. 9: Surface roughness and (0002) of GaN buffer layer deposited at 500 ° C. and 600 ° C. with respect to heat treatment time.
Figure showing the full width at half maximum of the X-ray diffraction peak of the surface

[Explanation of symbols]

 1 Sapphire substrate 2 GaN buffer layer 3 GaN single crystal layer

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

Claims (10)

[Claims] 1. A method comprising: depositing a GaN deposition layer using trimethylgallium; and depositing a GaN single crystal layer on the GaN deposition layer using triethylgallium at a temperature equal to or higher than the deposition temperature. Method for manufacturing gallium nitride-based semiconductor. 2. The deposition temperature of the GaN deposited layer is 500 ° C. or higher 60
The method for producing a gallium nitride-based semiconductor according to claim 1, wherein the temperature is 0 ° C. or lower. 3. The method for producing a gallium nitride-based semiconductor according to claim 1, wherein the substrate is a sapphire C plane. 4. A step of depositing a GaN deposition layer using trimethylgallium, and a step of heat-treating the substrate on which the GaN deposition layer is deposited at a temperature higher than the deposition temperature for a predetermined time in a gas atmosphere containing nitrogen atoms, And a step of depositing a GaN single crystal layer using triethylgallium at the deposition temperature or higher after the heat treatment, the method for producing a gallium nitride based semiconductor. 5. The method for producing a gallium nitride based semiconductor according to claim 4, wherein the heat treatment atmosphere is a mixed gas of ammonia and hydrogen. 6. The method for producing a gallium nitride-based semiconductor according to claim 4, wherein the heat treatment temperature is 1000 ° C. or higher. 7. The method for producing a gallium nitride-based semiconductor according to claim 4, wherein the heat treatment time is 1 hour or less. 8. GaN deposited using trimethylgallium
A gallium nitride-based semiconductor comprising: a low-temperature deposited layer; and a GaN single crystal layer deposited on the deposited layer by using triethylgallium at the deposition temperature or higher. 9. A semiconductor laser comprising the gallium nitride-based semiconductor according to claim 8 and a double hetero structure made of an AlGaInN-based semiconductor. 10. An InGaN layer is used as an active layer and Ga is used as a barrier layer.
The semiconductor laser according to claim 9, wherein an N layer is used.