JP3353527B2 - Manufacturing method of gallium nitride based semiconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a gallium nitride semiconductor used for a light emitting diode over a wavelength range from blue to ultraviolet or a semiconductor laser diode in the same wavelength range. The present invention relates to a method for vapor-phase growth of a gallium nitride based semiconductor having excellent characteristics.

[0002]

2. Description of the Related Art Blue light-emitting elements are expected as light sources for optical disks capable of full-color displays and high-density recording, and III-VI compound semiconductors such as ZnSe and III-crystals such as SiC and GaN.
-Active research has been made using Group V compound semiconductors.
In particular, recently, a blue light emitting diode has been realized using GaN, GaInN, or the like, and a light emitting element using a gallium nitride-based semiconductor has attracted attention. As a method for depositing a gallium nitride based semiconductor crystal, a metal organic chemical vapor deposition (MOVPE) method and a molecular beam epitaxy method (MBE method) are generally used.

For example, a deposition method using the MOVPE method will be described. An organometallic trimethylgallium (TMG) and ammonia (NH3) are placed in a reactor having a sapphire substrate.
Is supplied onto the substrate using hydrogen as a carrier gas,
After depositing a polycrystalline GaN buffer layer at about the temperature, the supply of TMG as a Ga
Raise the temperature to about 0 ° C. Next, TMG is supplied again on the substrate, and a GaN single crystal layer is deposited.

[0004] Other examples of the Ga source include triethyl gallium (TEG). In any case, the Ga source is the same in the vapor phase growth of the GaN buffer layer and the GaN single crystal layer. is there.

[0005]

However, in the vapor phase growth as in the conventional method, the electrical, optical,
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 source has excellent crystal structure, but has a level in the forbidden band due to residual impurities and defects. This makes it impossible to realize a semiconductor laser.

When TEG is used as a Ga raw material, a GaN single crystal excellent in crystal structure can be produced. However, in order to suppress surface irregularities, it is necessary to deposit a GaN buffer layer at a considerably low temperature. As a result, a large amount of impurities and defects were present in the buffer layer, and the optical properties of the GaN single crystal layer thereon were degraded. Increasing the deposition temperature of the GaN buffer layer to suppress impurities from entering the crystal
Becomes a single crystal and deposits on the substrate. In particular, on a sapphire substrate, since the lattice mismatch between the substrate and the GaN crystal is large, the unevenness of the surface becomes large and the element structure of the light emitting element cannot be deposited.

An object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing a gallium nitride-based semiconductor having excellent electrical, optical and crystal structures.

[0008]

Means for solving the above problems are as follows.

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

The second means is to use trimethylgallium on a substrate in the vapor phase growth of gallium nitride based semiconductor.
Depositing an N low-temperature deposition layer, heat-treating the substrate on which the GaN low-temperature deposition layer has been deposited at a temperature equal to or higher than the deposition temperature in a mixed gas atmosphere of ammonia and hydrogen for a predetermined time, and using triethylgallium after the heat treatment. Depositing a GaN single crystal layer at a temperature equal to or higher than the deposition temperature.
In particular, the heat treatment is a method for manufacturing a gallium nitride-based semiconductor in which it is effective to perform the heat treatment at 1000 ° C. or higher for one hour or less.

[0011]

According to the first method for producing a gallium nitride based semiconductor of the present invention, a polycrystalline GaN buffer layer can be deposited at a high temperature when depositing a GaN buffer layer using TMG. A small number of buffer layers can be formed.
When TEG is used as a source gas, the buffer layer is not polycrystalline at high temperature but becomes single crystal, so this layer is not suitable for the buffer layer. Here it becomes a single crystal,
Whether it becomes polycrystalline depends on the decomposition temperature of the source gas.
In other words, a single crystal is deposited when deposited at a temperature higher than the decomposition temperature of the source gas, and a polycrystal is deposited when deposited at a lower temperature. 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 polycrystal. By depositing at a high temperature, contamination with impurities can be reduced. In addition, since the buffer layer is polycrystalline, the surface can be made flat with small irregularities.

In summary, when a GaN buffer layer is deposited using TMG, the decomposition temperature of TMG is about 100 ° C. higher than the decomposition temperature of TEG. A polycrystalline GaN buffer layer containing less oxygen, which has a large influence on impurities, particularly crystallinity, can be deposited. The reason why the decomposition temperature of TMG is about 100 ° C. higher than that of TEG is that, as shown in FIGS. 2A and 2B, in TMG of FIG. 2A, the molecule directly bonded to Ga is a methyl group, and FIG. T shown in b)
This is probably because the binding energy is large because the mass is smaller than the ethyl group in the EG.

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

According to the second method of manufacturing a gallium nitride based semiconductor of the present invention, even if a GaN buffer layer in a polycrystalline state having a particularly poor crystallinity at a low temperature of 500 ° C. or less is deposited, a GaN single layer on the buffer layer is deposited. If heat treatment is performed at 1000 ° C. or higher in a mixed atmosphere of ammonia and hydrogen before crystal growth, the buffer layer can be monocrystallized to some extent.
When a single crystal is deposited, a GaN single crystal with good crystallinity can be obtained. The heat treatment is preferably performed within one hour, and if performed more than that, the unevenness of the surface increases, which has an adverse effect.

[0015]

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

(Embodiment 1) As shown in FIG. 1, a GaN buffer layer 2 is first deposited on a sapphire substrate C surface 1 using trimethylgallium (TMG). Crystal growth is performed by metal organic chemical vapor deposition (MOVPE).

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

Next, after cooling to 600 ° C.,
The GaN buffer layer 2 is deposited to a thickness of 50 nm by flowing μmol / min, ammonia at 2.5 L / min, and carrier hydrogen at 2 L / min.

Next, only the supply of TMG was stopped, and the temperature was reduced to 10%.
After the temperature was raised to 30 ° C., TEG was supplied at a rate of 60 μmol / min.
An aN single crystal layer 3 is deposited to a thickness of 1.2 μm. Next, only the supply of TEG is stopped, and the mixture is cooled to room temperature in a mixed atmosphere of ammonia and hydrogen.

The temperature profile and the gas supply profile described above are as shown in FIG.
The feature is that the mode is switched 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 the surface roughness (irregularities) when a GaN low-temperature deposited layer, that is, a buffer layer is grown on a sapphire substrate by the MOVPE method.

According to an experiment, when TMG is used as a source gas, a flat surface having a small roughness is used at a temperature of 600 ° C. or less, but when TEG is used, 500 ° C. is lower than that when TMG is used.
Only a flat surface could be obtained. It is considered that the roughness increases at high temperatures because the GaN single crystal starts to grow on the sapphire substrate with large lattice mismatch.
A flat GaN single crystal cannot be deposited on the buffer layer.

At temperatures below 500 ° C., almost no GaN was deposited on any of the raw materials. Therefore, when TEG is used as a raw material of the GaN buffer layer, the growth temperature is 5
The temperature is limited to around 00 ° C., and the quality of the GaN single crystal layer fluctuates with a slight change in conditions.

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

FIG. 5 shows GaN using TMG on a sapphire substrate.
7 shows a depth profile obtained by analyzing, using SIMS, residual impurities in a sample on which a buffer layer (low-temperature deposited layer, 600 ° C.) and a GaN single-crystal layer (high-temperature deposited layer, 1030 ° C.) are deposited. Cold deposition layers contain significant amounts 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 a defect to form a deep level, so that it is necessary to suppress this.

However, when TEG is used as a material for the buffer layer, the growth temperature of the buffer layer must be further lowered by 100 ° C., and the contamination and diffusion of impurities become more serious.
Therefore, it is understood that the use of TMG as the raw material of the GaN buffer layer is more effective from the viewpoint of impurity contamination.

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

First, from the viewpoint of impurity contamination, no impurity exceeding the detection limit was detected in the GaN single crystal layer deposited using TEG based on the result of the SIMS profile of FIG. 5 described above. However, carbon was detected in the GaN single crystal layer deposited using TMG at about 1.5 times the carbon level in the GaN single crystal layer deposited using TEG. 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, and all samples had high resistance.

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

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

As described above, the source gas of the buffer layer is T
By using MG and using TEG as the raw material of the single crystal layer,
A good GaN single crystal layer was obtained. The following table summarizes this.

[0032]

[Table 1]

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

(Example 2) A second deposition method of the laminated structure of the GaN crystal shown in FIG. 1 will be described. First, as shown by the temperature profile and the gas supply profile in FIG.
Prior to MOVPE vapor phase growth, the sapphire substrate 1 is placed on a susceptor in a reactor, evacuated, and then heated at 1100 ° C. for 15 minutes in a 70 Torr hydrogen atmosphere to clean the substrate surface. Next, after cooling to 500 ° C. or 600 ° C., TMG was 60 μmol / min and ammonia was 2.
At a flow rate of 5 L / min and a flow rate of carrier hydrogen of 2 L / min, a GaN buffer layer 2 is deposited to a thickness of 50 nm. Next, only the supply of TMG is stopped, the temperature is raised to 1030 ° C., and this state is maintained for one hour to perform heat treatment. Next, TEG was supplied at 60 μmol / min to supply GaN.
A single crystal layer 3 is deposited to a thickness of 1.2 μm. Next, only the supply of TEG is stopped, and the mixture is cooled to room temperature in a mixed atmosphere of ammonia and hydrogen.

In order to examine 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 (0002) plane X-ray diffraction peak are shown in FIG. It is. 500 ℃
It has been found that the roughness of the strong polycrystalline buffer layer deposited in step (1) increases when the heat treatment is performed for 30 minutes or more, and the buffer layer gradually becomes 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 became narrower in accordance with 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 the buffer layer is a thermally stable buffer layer substantially 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 the heat treatment hardly changes. As a result of the above heat treatment, polycrystalline GaN buffer layers with various degrees of single crystallization exist in the temperature range between 500 ° C and 600 ° C, and are optimal for relieving strain with substrates with large lattice mismatch. It was found that a polycrystalline state existed.

From the above results, a GaN buffer layer was deposited in a temperature range between 500 ° C. and 600 ° C., subjected to a heat treatment, deposited at 540 ° C., and then subjected to a heat treatment 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 is 90 seconds, which is the highest value that has not been reported so far, and a high-quality GaN single crystal with high resistance and very strong band edge emission is obtained. Was done.

From the results of this experiment, the heat treatment is preferably performed at a temperature of 1000 ° C. or higher. At a temperature lower than this temperature, the heat treatment takes too much time, and conversely, the crystallinity decreases. Also, the heat treatment time is preferably within one hour in order to avoid deterioration of crystallinity.

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

The heat treatment atmosphere is not only a mixed atmosphere of ammonia and hydrogen but also an atmosphere that can suppress 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 of the buffer layer is T
Although MG is used, since the heat treatment is performed after the buffer layer is deposited, TEG gas may be used as a raw material.

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

First, the GaN single crystal 3 shown in FIG. 1 has a low impurity concentration, a flat surface, and excellent C-axis orientation. Crystal growth.

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

[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 incorporation 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, the incorporation of impurities can be suppressed and a GaN single crystal layer having good C-axis orientation can be realized.

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

[Brief description of the drawings]

FIG. 1 shows a cross section of an experimental sample.

FIG. 2 is a diagram showing 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 deposited layer, that is, a buffer layer is grown on a sapphire substrate by MOVPE.

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

FIG. 6 is a diagram showing low-temperature (16K) photoluminescence of a GaN single crystal deposited using TMG or TEG.

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

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

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

[Explanation of symbols]

 Reference Signs List 1 sapphire substrate 2 GaN buffer layer 3 GaN single crystal layer

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hidemi Takeishi 1006 Odakadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-9-116130 (JP, A) JP-A-6 JP-A-6-268259 (JP, A) JP-A-6-268257 (JP, A) JP-A-4-209577 (JP, A) JP-A-2-81484 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00 H01L 21 / 205,21 / 31,21 / 365 JICST file (JOIS)

Claims (4)

(57) [Claims] A step of flowing trimethylgallium and ammonia into a reaction furnace at a deposition temperature of 500 ° C. or more and 600 ° C. or less to deposit a first semiconductor layer, which is a buffer layer made of polycrystalline GaN, on a substrate; A step of flowing triethylgallium and ammonia into the reaction furnace at a deposition temperature higher than the deposition temperature of the first semiconductor layer to deposit a second semiconductor layer composed of a single crystal layer directly on the first semiconductor layer A method for producing a gallium nitride-based semiconductor, comprising: 2. The method according to claim 1, further comprising a heat treatment step between the step of depositing the first semiconductor layer and the step of depositing the second semiconductor layer. 3. The method for producing a gallium nitride-based semiconductor according to claim 2, wherein the atmosphere gas in said heat treatment step contains nitrogen atoms. 4. A substrate, and a first semiconductor layer which is a buffer layer made of polycrystalline GaN deposited on the substrate by flowing trimethylgallium and ammonia at a deposition temperature of 500 ° C. or more and 600 ° C. or less, A second semiconductor layer consisting of a single crystal layer deposited immediately above the first semiconductor layer by flowing triethylgallium and ammonia at a deposition temperature higher than the deposition temperature of the first semiconductor layer. Gallium-based semiconductor.