JPWO2008117627A1 - AlGaN crystal growth method on silicon substrate - Google Patents

Abstract

Provided is a method for growing high-quality AlGaN crystals on a silicon substrate without complicated processing. The surface of the silicon substrate 1024 is terminated with hydrogen. First, heating is performed at 700 ° C. or higher, for example, about 950 ° C. to desorb hydrogen. After changing the carrier gas from hydrogen to nitrogen, the temperature is raised to the crystal growth temperature of AlGaN. At the same time, the raw material gas is introduced. In this way, AlGaN is epitaxially grown. Since AlGaN crystal growth was performed after desorption of hydrogen, a higher quality AlGaN crystal can be obtained.

Description

  The present invention relates to a method for crystal growth of AlGaN on a silicon substrate and related techniques.

  AlGaN is widely used as a material for light-emitting diodes and the like.

  MOVPE (Metalorganic Chemical Vapor Phase Deposition) is known as one of the methods for growing AlGaN crystals, and has been widely used. When AlGaN is crystal-grown by this MOVPE method, a sapphire substrate or a silicon carbide (SiC) substrate has been used as a substrate (referred to as a substrate crystal) as a base for the crystal growth.

  Since these substrates are very expensive, the use of inexpensive silicon substrates has long been considered.

Silicon substrate
However, it is known that when an AlGaN crystal is grown by the MOVPE method using this silicon substrate, it is difficult to continue high-quality crystal growth for a long time. The reason is considered to be that the source gas reacts with silicon.

  Also, for example, “http://www.sanken-ele.co.jp/news/contents/20011122.htm” (Sanken Electric, NEWS release) (Non-patent Document 3) on the Internet excludes Al from AlGaN. Similar problems have been pointed out with respect to GaN, which is a new material. This Non-Patent Document 3 also describes a method for solving the above problems.

  According to this description, firstly, in order to suppress the reaction between silicon and the GaN material, it is proposed that the silicon surface before epitaxial growth is made flat in atomic order and covered with hydrogen atoms. Yes. Second, in order to improve the crystallinity of GaN, it has been proposed to investigate various plane orientations of the silicon substrate and adopt the Si (111) plane having the best crystallinity. It is described that the general technical common sense that it is difficult to directly grow GaN crystals on a silicon substrate because Si and Ga react by such a method is described.

  Although shown here is the growth of GaN crystals, it is known that similar problems exist for AlGaN.

  Thus, it was difficult to grow an AlGaN crystal using a silicon substrate.

  Therefore, the idea that an AlGaN or GaN buffer layer may be formed on a silicon substrate before the epitaxial growth of AlGaN has long existed. However, it is known that when such a buffer layer is formed, irregularities and holes are formed on the substrate. This reason was thought to be because Si and Ga would react. This problem is also described in Non-Patent Document 1, for example. The state of the “hole” described in Non-Patent Document 1 relates to a GaN buffer layer, but AlGaN can be considered in a similar manner. This non-patent document 1 also includes a photograph showing the appearance of a “hole”.

Crystal growth of GaN and AlGaN by the improved conventional technique Therefore, it is difficult to adopt a buffer layer made of GaN, and in recent years, it has been considered to use a buffer layer made of AlN.

  When an AlN buffer layer is used, an AlN buffer layer is first provided on a silicon substrate at a low temperature. Next, crystal growth of GaN or AlGaN is performed at a high temperature.

Other prior art documents AlGaN and various other techniques are known for crystal growth of GaN.

  (A) A light-emitting diode using an AlN buffer layer as described above is described in Patent Document 1 below. This Patent Document 1 shows a structure in which a porous silicon layer is formed on a silicon substrate, a buffer layer made of AlN is formed thereon, and an InAlGaN layer is formed thereon (Matsushita Electric).

  (B) Patent Document 2 below shows a structure in which a multilayer buffer layer is formed on a silicon substrate. The buffer layer of Patent Document 2 has a structure in which a first layer made of AlN, a second layer made of GaN, and a third layer made of AlGaN are stacked repeatedly. It is described that the buffer layer becomes high resistance and the leakage current of HEMT decreases (Sanken Electric).

  (C) Patent Document 3 below shows an example in which an AlGaN buffer layer is used in a GaN-based semiconductor device. This Patent Document 3 shows a structure in which a SiC thin film layer is provided on a SiMOX substrate and an AlGaN buffer layer is formed thereon (Toshiba).

  (D) For example, a technique for depositing GaN on GaAs is known. In this technique, it can be said that it is preferable to grow GaN on the surface where arsenic is easily removed in consideration of the “front” and “back” surfaces of the GaAs crystal surface (111). Such a technique is described in Non-Patent Document 2 below.

  (E) Patent Document 4 below discloses a configuration in which a titanium nitride film is provided on a silicon substrate and GaN is stacked thereon.

  (C) Moreover, the following patent document 5 discloses a technique for providing irregularities on a silicon substrate. By this unevenness, even if GaN is directly grown without providing a low-temperature GaN buffer layer, it is possible to suppress the lateral growth of the crystal and to realize a flat crystal growth.

  (D) Patent Document 6 listed below discloses a technique for crystal growth of III-V nitride (particularly GaN) using a silicon substrate on which a natural oxide film is formed. Patent Document 3 discloses a technique in which the natural oxide is nitrided and converted to a SiON film, and then a III-V nitride (particularly GaN) is crystal-grown on the SiON film.

  (E) Patent Document 7 listed below describes a technique comprising two stages of growth as a method for growing a nitride semiconductor crystal. First, in the first stage, island-like crystal regions are formed on a substrate (base) at a low crystal growth rate at a low temperature. In the second stage, a technique is disclosed in which crystal growth is performed at a high temperature and a high crystal growth rate so as to bond island-like crystal regions.

  (F) In Patent Document 8 below, an amorphous layer of GaN is formed on a base plate made of a GaN single crystal, and a single crystal layer of GaN is further formed on the amorphous layer. A description is disclosed. It is said that crystal defects such as dislocations are reduced.

  (G) In Patent Document 9 below, a 3C—SiC single crystal layer and a BGaN mixed crystal layer are sequentially provided on a single crystal silicon substrate. Then, a c-GaN single crystal film is formed on these. It is described that a GaN semiconductor capable of controlling defects can be obtained.

  (H) Patent Document 10 below discloses a technique in which a c-BP film is formed on a silicon substrate as a buffer layer, and 3C-SiC or c-GaN is epitaxially grown on the buffer layer. Yes. It is described that the problem of lattice mismatch can be solved. Also disclosed is a technique for forming an amorphous SiC or GaN film at 300 ° C. to 600 ° C. on the c-BP buffer layer.

JP 2006-303154 A (Matsushita Electric Industrial Co., Ltd.) JP 2005-158889 (Sanken Electric) JP 09-223819 A (Patent No. 3409958) (Toshiba) JP 2000-031534 A (Sunken) JP 2002-289540 A (Mitsubishi Electric Cable) Japanese Patent Laid-Open No. 10-163528 (Furukawa Electric) JP 2002-313733 A (Sony) JP 2000-340509 A (Sumitomo Electric Industries) JP-A-2005-32766 (Toshiba Ceramics) JP 2004-22581 A (Toshiba Ceramics) A. Dadgar, M. Poscherieder, J. Blasing, et al., "MOVPE growth of GaN on Si (111) substrates", J. of Crystal Growth 248 (2003), pp556-562 Yoshinao Kumagai, Akinori Koukitu, Hisashi Seki, "Investigation of Substrate Orientation Dependennce for the Growth of GaN on GaAs (111) A and (111) B Surfaces by Metalorganic Hydrogen Chloride Vapor-phase Epitaxy", Jpn. J. Appl. Phys. , Vol.39 (2000), pp.L149-L151, Part2, No.2B, 15 February 2000 "Development of GaN-based high-efficiency blue LED using silicon substrate", NEWS release, November 2001, Sanken Electric, [Search February 8, 2005], Internet <URL: http: //www.sanken- ele.co.jp/news/contents/20011122.htm>

  As described above, there are various attempts to perform AlGaN crystal growth on a silicon substrate, but these have the following problems.

  (1) In the technique of using AlN or other substances as a buffer layer, the material used increases, and the apparatus tends to be complicated. In addition, since the types of materials increase, the management cost of the materials also increases.

  (2) Further, in the method of performing some processing on the surface of the silicon substrate, it is necessary to process the surface to “roughen”, and there is a possibility that a problem in flatness may occur. Moreover, the process for a process is needed and there exists a possibility that the crystal growth method may become complicated.

  Therefore, a technique capable of growing a high-quality AlGaN crystal on a silicon substrate by a simpler technique is widely desired.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for growing an AlGaN crystal on a silicon substrate without complicated processing.

  As described above, silicon substrates (Si substrates) are widely available as large substrate crystals in the world, so that if they can be used as substrates, it is possible to manufacture optical elements and electronic devices at a very low cost. Therefore, as already described, many studies have been made on crystal growth of AlGaN on a silicon substrate.

  As described above, when AlGaN is epitaxially grown on Si under normal conditions, a hole-like defect is generated at the AlGaN-Si interface, and it is expected that good crystal growth of AlGaN cannot be achieved. There have been many reports (papers and conference presentations) that capture this phenomenon and generally cause a reaction between the substrate Si and a Ga molecular species as a raw material.

  Currently, one of the most popular techniques for solving this problem would be the use of the buffer layer described above. That is, an AlN thin film (buffer layer) is first grown on a Si substrate, and then GaN is grown. LEDs are actually made using this technology and are commercially available. This is described in Non-Patent Document 3 above.

By the way, the inventors of the present application have studied for a long time a method of growing AlGaN on a Si substrate.

  As a result, the inventors of the present application normally do not react Si and Ga raw materials, but cause defects such as holes in the silicon substrate when AlGaN is directly grown on a silicon substrate. It was found that hydrogen in the gas phase atmosphere was adsorbed on the outermost surface of Si and the adsorbed hydrogen hindered the growth of AlGaN.

For example, if a GaN buffer layer is to be grown there, it is considered that the growth is hindered and a hole is formed in this layer. The inventors of the present invention have clarified that NH ₃ and Si, which are raw materials, react through the holes during AlGaN growth at a high temperature, and the interface becomes uneven.

  Through these studies, in order to grow AlGaN directly on a Si substrate, the inventors have fully desorbed hydrogen adsorbed on Si in an atmosphere without hydrogen (or sufficiently small), and then AlGaN. The inventors have invented a method for performing epitaxial growth.

  According to this method, a good quality AlGaN crystal can be obtained. The inventors of the present application actually executed this method and grown AlGaN on a Si substrate to obtain an AlGaN crystal. This AlGaN crystal was confirmed to be a high-quality AlGaN crystal capable of PL emission.

  Specifically, the present invention employs the following means.

  (1) In order to solve the above problems, the present invention provides a method for crystal growth of AlGaN on a silicon substrate, wherein a hydrogen desorption step for desorbing hydrogen atoms on the silicon substrate, and a hydrogen desorption step And a crystal growth step of crystal growth of AlGaN on the silicon substrate.

  As described above, since hydrogen atoms on the silicon substrate are desorbed, it is possible to prevent hydrogen from interfering with AlGaN crystal growth. Then, if AlGaN crystal growth is performed, a good quality AlGaN crystal can be obtained.

  (2) Further, in the AlGaN crystal growth method according to the above (1), the hydrogen desorption step includes a step of heating the silicon substrate to a temperature of 700 ° C. or higher. This is a crystal growth method.

  Hydrogen can be eliminated by heating. The heating temperature is more preferably 800 ° C. or higher, and even more preferably 900 ° C. or higher.

  (3) Further, in the AlGaN crystal growth method according to the above (1), the hydrogen desorption step includes a step of placing the silicon substrate in a nitrogen atmosphere at a temperature of 700 ° C. or higher. This is an AlGaN crystal growth method.

  When heating, under a nitrogen atmosphere not containing hydrogen, it is possible to prevent hydrogen from being bound (terminated) to the surface again. The temperature in the nitrogen atmosphere is more preferably 800 ° C. or higher, and even more preferably 900 ° C. or higher.

  As shown in the embodiments described later, even when hydrogen is contained in the initial stage of heating, the case where the atmosphere is changed to an atmosphere not containing hydrogen during heating is also included in the technical scope of the present invention.

  (4) Further, according to the present invention, in the AlGaN crystal growth method according to the above (1), the hydrogen desorption step includes a step of placing the silicon substrate in an inert gas atmosphere having a temperature of 700 ° C. or higher. An AlGaN crystal growth method characterized by the following.

  When heating is performed in an inert gas atmosphere containing no hydrogen, it is possible to prevent hydrogen from being bonded (terminated) to the surface again. The temperature of the inert gas is more preferably 800 ° C. or higher, and even more preferably 900 ° C. or higher.

  (5) Further, according to the present invention, in the AlGaN crystal growth method according to the above (1), the crystal growth step includes a step of growing an AlGaN crystal in an atmosphere not containing hydrogen. This is a crystal growth method.

  (6) In the AlGaN crystal growth method according to (1), the hydrogen desorption step is a step of changing the atmosphere around the silicon substrate to an atmosphere containing no hydrogen in the step. And the crystal growth step includes a step of introducing a source gas into the atmosphere after the change, further setting a temperature to a crystal growth temperature, and growing an AlGaN crystal on the silicon substrate. This is an AlGaN crystal growth method.

  With such a configuration, since there is no interference by hydrogen atoms when forming the AlGaN crystal, a higher quality AlGaN crystal can be obtained.

  As described above, according to the present invention, hydrogen atoms are desorbed from the surface of the silicon substrate, and as a result, it is possible to grow AlGaN crystals thereon.

It is a schematic diagram of the crystal growth apparatus used in this Embodiment. It is a conceptual diagram of the AlGaN crystal growth method demonstrated in this Embodiment. It is a graph showing the temperature change etc. in the case of crystal growth in this Embodiment. It is a graph which shows the relationship between the ratio of hydrogen gas, and a coverage. A graph showing the relationship between the proportion of AlCl ₃ in the source gas and the Al composition in the obtained AlGaN crystal is shown. It is an X-ray profile of the AlGaN crystal (Al composition 55%) created in the present embodiment. It is a graph which shows the result of having measured the optical physical property of the AlGaN crystal (Al composition 55%) created in this Embodiment using photoluminescence measurement. It is a SEM (scanning electron microscope) photograph which shows the mode of the silicon substrate surface at the time of providing a GaN buffer layer on Si substrate. It is a microscope picture of sectional drawing at the time of growing an AlGaN crystal about 1 micrometer on Si substrate by the method demonstrated in this Embodiment. 10 is a photomicrograph when the cross section of FIG. 9 is viewed obliquely from above about 20 degrees.

Explanation of symbols

1000 GaN crystal growth apparatus 1012 Aluminum raw material supply unit 1012a First gas introduction path
1014 Gallium source supply section 1014a Second gas introduction path 1016 Nitrogen source supply section 1016a Third gas introduction path 1018 Mixing section 1020 Growth section 1020a Discharge port 1022 AlGaN
1024 substrate crystal, Si substrate (silicon substrate)

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present embodiment, as a method for growing an AlGaN crystal on a silicon substrate, a preferred embodiment of a technique for performing epitaxial growth after dehydrogenation will be described.

As described in Chapter 1 Principle Background Art, when a GaN buffer layer is formed on a silicon substrate, for example, it is known that the surface flatness is lost, for example, there is a hole in the substrate surface. As a result, even if an AlGaN crystal was epitaxially grown on the GaN buffer layer, a good quality GaN crystal could not be obtained. Conventionally, it has been customary to say that the cause of holes in the substrate surface is that Si and Ga react.

  The inventor of the present application considered that this general theory is not necessarily a valid reason, and thought that the cause of the occurrence of holes and the like was hydrogen atoms existing on the surface of the silicon substrate. And we were able to confirm the validity of this idea through experiments.

The result of this experiment is shown in FIG. FIG. 8 is a SEM (scanning electron microscope) photograph showing the state of the silicon substrate surface when a GaN buffer layer is provided on the silicon substrate. The film formation conditions for these GaN buffer layers are: a gas atmosphere in which the partial pressure of TMG gas is 2.0 × E-5 atm, the partial pressure of NH ₃ gas is 0.2 atm, and the temperature is 640 ° C. The film was formed. The total pressure of this gas is 1 atm. This condition is common to FIGS. 8 (1), (2), and (3).

  The difference between (1), (2) and (3) in FIG. 8 is the carrier gas used.

FIG. 8 (1) is an example using a carrier gas which is all N ₂ . In this embodiment, the hydrogen partial pressure ratio in the carrier gas is referred to as “F”. That is, in FIG. 8 (1), F = 0 (hydrogen partial pressure ratio is 0).

  As shown in FIG. 8A, it is clearly shown that the GaN buffer layer covers the entire surface of the silicon substrate at the hydrogen partial pressure ratio F = 0.

Next, in FIG. 8 (2), N ₂ + H ₂ was used as a carrier gas. In this case, the hydrogen partial pressure ratio F = 0.1. That is, this is an example using a carrier gas containing 10% hydrogen.

  As shown in FIG. 8 (2), at the hydrogen partial pressure ratio F = 0.1, although the GaN buffer layer covers the silicon substrate surface, there are some places where the silicon substrate is partially exposed. . Thus, it is clear from the photograph that the GaN buffer layer has holes partially opened.

Next, in FIG. 8 (3), H ₂ was used as a carrier gas. In this case, since the carrier gas is all hydrogen gas, the hydrogen partial pressure ratio F = 1.0.

  As shown in FIG. 8 (3), at the hydrogen partial pressure ratio F = 1.0, the GaN buffer layer is only scattered in an island shape on the surface of the silicon substrate, and most of the silicon substrate is not covered. Is exposed. Thus, the GaN buffer layer is hardly formed.

  From these facts, it is clear that the surface homology of the GaN buffer layer depends on the hydrogen partial pressure. Then, it was found that the formation of the GaN buffer layer is hindered when hydrogen is contained in the apparatus system during film formation (specifically, in the carrier gas) even at only 10 percent.

  As a result of the above, the inventors of the present invention use a carrier gas having a hydrogen gas partial pressure ratio of 0 or almost close to 0 to desorb hydrogen on the surface of the silicon substrate, and then grow AlGaN on the silicon substrate. Thus, a new AlGaN crystal growth method has been realized.

Chapter 1-2 Apparatus Configuration A schematic diagram of a vapor phase growth apparatus 1000 used in the present embodiment is shown in FIG.

  The vapor phase growth apparatus 1000 includes an aluminum source supply unit 1012 that supplies an aluminum source, a gallium source supply unit 1014 that supplies a gallium source, and a nitrogen source supply unit 1016 that supplies a nitrogen source. The gas output from each supply unit is mixed in the mixing unit 1018 and then used for crystal growth in the growth unit 1020. The growth unit 1020 is composed of a quartz reaction chamber and is provided with an exhaust port 1020a.

As shown in FIG. 1, the aluminum raw material supply unit 1012 is a reaction chamber in which metallic aluminum is accommodated in a predetermined reaction chamber. The aluminum material supply portion 1012, first gas introduction passage 1012a is provided, and HCl through the first gas inlet passage 1012a, and hydrogen gas _{H 2,} nitrogen gas _{N 2} is introduced. The ratio of hydrogen gas to nitrogen gas will be described in detail later.

As a result, the metal aluminum and these gases react to produce AlCl ₃ which is an AlGaN aluminum material. The generated AlCl ₃ is transferred to the mixing unit 1018 together with the carrier gas.

  Note that the aluminum raw material supply unit 1012 is maintained at a predetermined temperature by using a heating device (not shown).

As shown in FIG. 1, the gallium source supply unit 1014 is a reaction chamber in which metallic gallium is accommodated in a predetermined reaction chamber. The gallium material supply portion 1014, the second gas introduction path 1014a is provided, and HCl through the second gas introducing passage 1014a, and hydrogen gas _{H 2,} nitrogen gas _{N 2} is introduced. As a result, metal gallium and these gases react to generate GaCl, which is a gallium raw material for AlGaN. The GaCl thus obtained is transferred to the mixing unit 1018 together with the carrier gas.

Nitrogen source supply unit Nitrogen source supply unit 1016 is a predetermined reaction chamber as shown in FIG. The nitrogen material supply portion 1016, third and gas introducing passage 1016a is provided, the hydrogen gas _{H 2} through the third gas introduction passage 1016a, a nitrogen gas _{N 2,} ammonia NH ₃ is introduced .

Although not shown, a heating device is provided around the nitrogen raw material supply unit 1016 and is heated to a predetermined temperature. With this heat, the ammonia NH ₃ in the nitrogen raw material supply unit 1016 is placed in a state of being decomposed at a predetermined rate. A mixed gas of ammonia NH ₃ decomposed at such a predetermined ratio, hydrogen gas H ₂ , and nitrogen gas N ₂ is transferred to the mixing unit 1018.

The mixing unit mixing unit 1018 mixes the source gases supplied from the above-described source units of the aluminum source supply unit 1012, the gallium source supply unit 1014, and the nitrogen source supply unit 1016. Moreover, in order to maintain at predetermined temperature, the predetermined heating apparatus not shown is provided.

The growth part growth part 1020 accommodates a substrate crystal (Si substrate 1024 (silicon substrate)) for crystal growth. In order to obtain a temperature suitable for crystal growth, a predetermined heating device (not shown) is provided. Such a heating apparatus can employ various configurations that have been known in the past. For example, heating with a heating wire or high-frequency heating can be used.

  In the present embodiment, a Si substrate 1024 is placed in the growth unit 1020, and AlGaN 1022 grows on this Si substrate 1024.

Chapter 1 3 Crystal Growth Flow FIG. 2 shows a conceptual diagram of the AlGaN crystal growth method described in the present embodiment. First, in FIG. 2A, the surface of the Si substrate 1024 is terminated with hydrogen. Next, in FIG. 2 (2), this hydrogen is desorbed. This point is characteristic in the present embodiment. Then, AlGaN is epitaxially grown on the surface from which hydrogen has been removed, and an AlGaN crystal layer 1022 is formed.

Chapter 2 Specific Example Based on the principle described in Chapter 1 and the apparatus used, a specific processing flow for actually growing an AlGaN crystal will be described.

2.1 Operation of Crystal Growth Crystal growth of AlGaN is performed using a crystal growth apparatus 1000 as shown in FIG. Changes in temperature and carrier gas at that time are shown in the graph of FIG. In the graph of FIG. 3, the horizontal axis represents elapsed time, and the vertical axis represents temperature (° C.).

As shown in this graph, the Si substrate 1024 is first cleaned with HF, and immediately after cleaning, the surface of the silicon substrate is terminated with hydrogen atoms and is stable. From this state, the temperature is increased to 250 ° C. and preheating is performed. Carrier gas used at this time is H _2.

  After preheating at 250 ° C. for about 10 minutes, the temperature is raised to 950 ° C. and maintained at that temperature. As a result, the terminating hydrogen atom is desorbed. That is, this desorption causes the hydrogen coverage to be 0%.

As a result, a clean Si surface (silicon surface) can be formed. When heating at 950 ° C. is continued for about 15 minutes, the carrier gas is replaced with N _{2 so} that new hydrogen atoms do not terminate on the surface.

One of the characteristic matters in the present embodiment is the presence of a heating step by replacing this carrier gas with N ₂ . Since it is replaced with N ₂ , hydrogen is newly prevented from terminating on the Si surface.

  After heating at 950 ° C. for about 10 minutes, the temperature is further raised to 1100 ° C. or higher, and AlGaN is epitaxially grown. Of course, the source gas will be introduced accordingly. In this way, crystal growth of AlGaN is performed.

Hydrogen Coverage Now, when switching to the nitrogen carrier gas described with reference to FIG. 3, if the mixing is performed while controlling the ratio of hydrogen gas, the hydrogen coverage that terminates the surface of the Si substrate changes.

  A graph for explaining this phenomenon is shown in FIG. FIG. 4 shows a graph showing the relationship between the hydrogen gas ratio and the coverage. In the graph of FIG. 4, the horizontal axis represents the ratio of hydrogen gas, and the vertical axis represents the coverage. In the graph of FIG. 4, the hydrogen coverage is 0 in the “0” on the horizontal axis, that is, the complete “nitrogen” system.

  On the other hand, in the case of “1” on the horizontal axis, that is, the complete “hydrogen” system, the coverage is 0.56. Thus, AlGaN growth is hindered when hydrogen is present on the surface of the Si substrate, and it is difficult to grow a uniform film.

Adjustment of Al composition Next, in the present embodiment, it is possible to adjust the composition of the obtained crystal by changing the ratio of the raw material gas. In the present embodiment, the Al composition can be changed from 0% to 100% by changing the proportion of AlCl _{3 in} the group III raw materials (AlCl ₃ and GaCl).

FIG. 5 shows a graph showing the relationship between the proportion of AlCl _{3 in} the source gas and the Al composition in the obtained AlGaN crystal. In this graph, the horizontal axis represents the proportion of AlCl ₃ (Al raw material vapor phase supply ratio: R), and the vertical axis represents the Al composition in the AlGaN crystal (solid phase composition ratio x). Here, the solid layer composition ratio x is x in Al _x Ga _1-x N.

  Then, X-ray diffraction was performed on the AlGaN crystal (Al composition 55%) grown on the Si substrate 1024 by the process as described above. The result is shown in FIG. FIG. 6 shows an X-ray diffraction profile, in which the horizontal axis represents an angle (degree) and the vertical axis represents a signal intensity (arbitrary unit).

  As is clear from this profile, only the intensity peak due to the Si (111) plane and AlGaN having an Al composition of 55% was observed, confirming that AlGaN was epitaxially grown.

  Next, the optical physical properties of the same AlGaN crystal (Al composition 55%) as above were measured using room temperature photoluminescence measurement. A graph representing the result is shown in FIG. The vertical axis of this graph is the emission intensity (arbitrary unit), and the horizontal axis is the emission wavelength. As shown in this graph, it was possible to emit light having a strong peak at 308 nm. As a result, it was confirmed that a high-quality AlGaN crystal was grown, similar to the result of the X-ray profile.

2.2 Actual state of the AlGaN crystal on the Si substrate The AlGaN crystal could be grown on the Si substrate by the method described above. An AlGaN crystal having a thickness of about 1 μm was grown on a Si substrate, and a cross-sectional view thereof was taken with an electron micrograph. This is shown in FIG. From FIG. 9, it was confirmed that the interface between the Si substrate and the AlGaN layer was not deteriorated. It was also confirmed that a uniform crystal growth of the AlGaN layer was actually possible on the Si substrate. The black area in FIG. 9 is in the air.

  FIG. 10 shows a photograph of a cross section similar to that shown in FIG. 9 observed with an electron microscope at an angle of about 20 degrees from the cross section.

Chapter 3 Modification (1) In the above-mentioned example, hydrogen was desorbed at 950 ° C., but by experiments conducted by the inventors of the present application, hydrogen is efficiently desorbed at approximately 700 ° C. or higher. It turns out that you can. Therefore, the hydrogen desorption process is preferably performed at a temperature of 700 ° C. or higher.

  (2) In the above-described example, when hydrogen is desorbed by heating, the carrier gas is changed from hydrogen to nitrogen, and the atmosphere is in a nitrogen atmosphere. This prevents hydrogen from adhering to the Si substrate again, but it is preferable because the same effect can be expected even if the atmosphere at that time is an inert gas atmosphere instead of a nitrogen atmosphere.

  It has been found through experiments by the present inventors that the temperature of nitrogen gas or inert gas is more preferably 800 ° C. or higher, and even more preferably 900 ° C. or higher.

  (3) In the example described above, AlGaN crystal was grown immediately after desorption of hydrogen. However, in some cases, a buffer layer was stacked on the Si substrate, and the AlGaN crystal was formed on the buffer layer. It is also preferable to cause the growth.

Claims (6)

In a method for crystal growth of AlGaN on a silicon substrate,
A hydrogen desorption step of desorbing hydrogen atoms on the silicon substrate;
After the hydrogen desorption step, a crystal growth step for crystal growth of AlGaN on the silicon substrate;
An AlGaN crystal growth method comprising: In the AlGaN crystal growth method according to claim 1,
The AlGaN crystal growth method, wherein the hydrogen desorption step includes a step of heating the silicon substrate to a temperature of 700 ° C. or higher. In the AlGaN crystal growth method according to claim 1,
The AlGaN crystal growth method, wherein the hydrogen desorption step includes a step of placing the silicon substrate in a nitrogen atmosphere at a temperature of 700 ° C. or higher. In the AlGaN crystal growth method according to claim 1,
The AlGaN crystal growth method, wherein the hydrogen desorption step includes a step of placing the silicon substrate in an inert gas atmosphere having a temperature of 700 ° C. or higher. In the AlGaN crystal growth method according to claim 1,
The AlGaN crystal growth method, wherein the crystal growth step includes a step of growing an AlGaN crystal in an atmosphere containing no hydrogen. In the AlGaN crystal growth method according to claim 1,
The hydrogen desorption step includes a step of changing the atmosphere around the silicon substrate to an atmosphere containing no hydrogen in the step,
The crystal growth step includes a step of introducing a source gas into the atmosphere after the change, further setting a temperature to a crystal growth temperature, and growing an AlGaN crystal on the silicon substrate. Crystal growth method.

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