JP4298023B2 - Nitride semiconductor multilayer deposition substrate and method for forming nitride semiconductor multilayer deposition substrate - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a multilayer deposited substrate or multilayer film of a group nitride semiconductor having a low crystal defect density suitable for forming a group III nitride semiconductor device, and a method for forming them.
[0002]
[Prior art]
Conventionally, high efficiency by direct transition using a group III nitride semiconductor (general structural formula is AlxGa1-xyInyN using aluminum Al, gallium Ga, indium In, nitrogen N, composition ratio x, y) Short wavelength laser oscillation has been reported. The substrate for forming such a laser must have a low crystal defect density, but the group III nitride semiconductor has a size that is small enough to withstand practical use, sapphire, SiC, spinel, MgO, GaAs, Si For example, a deposition substrate in which a group III nitride semiconductor is deposited on a different kind of substrate is used.
[0003]
However, there are considerable lattice mismatches and thermal expansion coefficient differences between these dissimilar substrates and Group III nitride semiconductors. For example, there is a 11-23% lattice mismatch and a thermal expansion coefficient difference of about 2 × 10 −6 K−1 between the sapphire substrate and the group III nitride semiconductor. For this reason, the crystallinity of the thin film or layer of the group III nitride semiconductor deposited on the dissimilar substrate deteriorated, and the electrical or optical characteristics of the thin film deteriorated.
[0004]
Therefore, attempts have been made to improve the crystallinity of the deposited substrate. Among them, a method of obtaining a multilayer deposition substrate by epitaxially growing several layers of a low temperature deposition buffer layer and a single crystal layer of a group III nitride semiconductor alternately on a different substrate is effective. In the literature, the buffer layer is also referred to as the buffer layer. Since the buffer layer also includes a buffer layer grown at a high temperature (growth at a single crystal growth temperature), the buffer layer formed at a temperature at which the single crystal does not grow is distinguished as a low temperature deposition buffer layer.
[0005]
In Japanese Patent Laid-Open No. 4-297030, Nakamura describes a single crystal layer of a gallium nitride semiconductor on an AlxGa1-xN (where x is 1 or less and greater than 0) buffer layer formed at a temperature at which the single crystal does not grow on the substrate. It is claimed that a higher quality gallium nitride semiconductor single crystal layer can be obtained by growing a single crystal layer of gallium nitride semiconductor on the AlN buffer layer.
Furthermore, when growing a GaN thin film on a substrate, it is better to use a GaN buffer layer than to use an AlN buffer layer.
“(1) Since the melting point is low, it is easy to crystallize easily when the temperature rises. Therefore, even if the thickness of the buffer layer is increased, the effect as the buffer layer can be expected.
(2) Since the buffer layer is GaN, when an epitaxial growth layer of GaN is grown thereon, the same material is grown on the same material, so that the crystallinity can be improved. It is thought that there are advantages such as. ”
[0006]
In Japanese Patent Laid-Open No. 9-199759, Akasaki et al. Alternated a substrate of a different material, that is, a low-temperature deposition buffer layer formed at a temperature at which the single crystal does not grow on the heterogeneous substrate and a single crystal layer formed at a temperature at which the single crystal grows. Discloses a technique in which three or more layers are stacked and a target group III nitride semiconductor layer is formed at a temperature at which a single crystal grows thereon. Three layers of AlN low temperature deposition buffer layers (deposition temperature 400 ° C., film thickness 50 nm) and GaN single crystal layers (growth temperature 1150 ° C., film thickness 300 nm, but only the uppermost film thickness is 1.5 μm) are laminated alternately. Examples have been disclosed. Etch pit density measured by electron scanning microscope after etching the top GaN single crystal layer with KOH is 4 × 10 7 cm −2 after deposition of one layer on the sapphire substrate, and 8 × 10 5 cm −3 when three layers are deposited. 2.
[0007]
In the specification of Japanese Patent Application No. 9-306215, Amano et al. Improved the above-mentioned method of red coral and the like so that a low temperature deposition buffer layer formed at a temperature at which a single crystal does not grow is subjected to temperature crystallization.
However, it is still desirable to improve the crystallinity of the deposited substrate. In particular, it is desired to grasp the stacking limit of the multilayer deposition substrate, improve the controllability of the quality of the multilayer deposition substrate, reduce the cost of the multilayer deposition substrate, and expand the application.
[0008]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to improve the crystallinity of a multilayer nitride substrate or multilayer thin film of a group nitride semiconductor.
Furthermore, it is to improve the quality controllability of the multi-layer deposition substrate, provide a method for obtaining a substrate of appropriate quality, and eliminate or reduce the problems of the prior art.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have clarified the mechanism by which the tensile strain in the growth surface is increased by the multi-layer deposition and leads to the generation of cracks, and have made the invention.
First, a nitride semiconductor multilayer deposition substrate according to the present invention is a multilayer deposition substrate including a plurality of layer pairs each including a low-temperature deposition buffer layer of nitride semiconductor and a single crystal layer of nitride semiconductor deposited immediately above the nitride semiconductor multilayer deposition substrate. The single crystal layer of the layer pair performs strain transfer to the compressive strain side in the growth plane with respect to the single crystal layer of the layer pair deposited by the layer pair.
[0010]
In the present invention, the crystallinity can be improved by selecting the number of layer pairs of 3 or more, and the crystallinity can be further improved by selecting the number of layer pairs of 4 or more. The nitride semiconductor multilayer deposition substrate according to claim 1, wherein:
[0011]
It is also advantageous to dope at least one of the layer pairs to reduce resistance.
[0012]
2. The nitride according to claim 1, wherein the low temperature deposition buffer layer is GaN and the single crystal layer is GaN in all of the layer pairs of 5 to 8 pairs in succession. Semiconductor multilayer deposition substrate.
[0013]
The method of the present invention is a method of forming a multi-layer deposition substrate comprising a plurality of layer pairs consisting of a nitride semiconductor low temperature deposition buffer layer and a nitride semiconductor single crystal layer deposited directly thereon.
Providing the one layer pair in which a single crystal layer included in the one layer pair generates a tensile strain in a growth plane;
The single crystal layer of the layer pair deposited on the single crystal layer included in the one layer pair has compressive strain along the growth surface;
It is characterized by providing.
[0014]
The method for forming a nitride semiconductor multilayer deposition substrate according to claim 11, wherein at least one of the tensile strain and the compressive strain can be observed at least at room temperature.
The magnitude of strain can be determined by measuring the lattice constant.
[0015]
Further, in a multilayer deposition substrate comprising a plurality of layer pairs each comprising a nitride semiconductor low temperature deposition buffer layer and a nitride semiconductor single crystal layer deposited immediately above the nitride semiconductor multilayer deposition substrate, at least two types of the layer pairs are provided. And one of the two types of layer pairs has less flexibility than the other and can be configured to include the at least one single crystal layer. .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Utilizing the above-mentioned technologies such as Amano, where a low temperature deposition buffer layer formed at a temperature at which a single crystal does not grow on a heterogeneous substrate or the same type substrate and a single crystal layer formed at a temperature at which the single crystal grows are alternately grown. As a result of experiments, the following findings were obtained.
[0017]
“Experiment 1”:
“Experiment 1” will be described with reference to FIG. 1, 3, and 7 schematically show the structures of the multilayer deposition substrates 10, 30, and 50, and do not use actual dimensions.
Step 1:
(Washing of substrate): A sapphire substrate (2-inch substrate) 11 having a (0001) C surface is etched by immersing it in hydrofluoric acid and aqua regia for 5 minutes each and rinsed with pure water for 5 minutes. Then, after organic washing with methanol and acetone for 5 minutes each, rinsing again with pure water for 5 minutes.
[0018]
Step 2:
(Substrate cleaning): The sapphire substrate 12 that has undergone the above steps at room temperature is transferred into a reaction furnace of a MOVPE (metal organic chemical vapor deposition method) apparatus. After sufficiently replacing the inside of the reaction furnace with nitrogen to remove oxygen and moisture, hydrogen is introduced and the sapphire substrate is heated and cleaned at 1100 ° C. for 10 minutes.
[0019]
Step 3:
(Formation of GaN low temperature deposition buffer layer): Thereafter, the temperature of the sapphire substrate 12 is set to 500 ° C., TMGa (trimethylgallium) and ammonia are supplied into the furnace for about 3 minutes, and the GaN low temperature of 30 nm is formed on the sapphire substrate 12. The deposition buffer layer 14 is grown and the supply of TMGa is stopped.
[0020]
Step 4:
(Formation of n-type GaN single crystal layer 16): After the growth of the GaN low-temperature deposition buffer layer 14, the temperature of the sapphire substrate 12 is increased to 1050 ° C. in about 3 minutes, and after about 5 minutes, TMGa (trimethylgallium) and Ammonia is supplied to start the growth of the GaN layer 16. When 1 μm is grown at a growth rate of 2.5 μm per hour, the supply of TMGa is stopped. The temperature of the sapphire substrate is also lowered to 500 ° C. During this time, the supply of ammonia continued.
[0021]
Step 5:
(Repeated formation of GaN low temperature deposition buffer layer 14 and GaN single crystal layer 16): Step 3 and step 4 are repeated a desired number of times to form a layer pair consisting of the GaN low temperature deposition buffer layer 14 and the GaN single crystal layer 16. . FIG. 1 shows a layer structure of a multilayer deposition substrate 10 after two pairs of layers are stacked.
Step 6:
(Observation of the growth surface of the uppermost GaN single crystal layer 16): The temperature of the multilayer deposition substrate 10 is lowered to room temperature, and the necessary measurements are taken out from the furnace. The measurement is the observation of the surface with a differential interference microscope and the measurement of the lattice constant of the single crystal layer with an X-ray diffractometer. In FIG. 2, the growth surface of the uppermost GaN single crystal layer 16 according to the number of layer pairs is observed with a differential interference microscope. 2A to 2E are photographs of observation results of the growth surface of the uppermost GaN single crystal layer 16 when the number of layer pairs is 2, 3, 6, 9, and 12, respectively, using a differential interference microscope.
[0022]
Also, in FIG. 5, changes in the c-axis lattice constant of the uppermost GaN single crystal layer 16 when the number of layer pairs is 2, 3, 6, 9, 12 are plotted as curve 1. The horizontal axis of the graph of FIG. 5 is the number of layer pairs, and the vertical axis is the c-axis lattice constant in units of 0.1 nm. The c-axis lattice constant of the surface is larger than the bulk lattice constant of about 0.5185 nm when the layer pair number is 1, but when the layer pair number is 2 or more, the lattice constant is smaller than the bulk lattice constant and becomes smaller as the layer pair number becomes larger. If the number of layer pairs is 2 or more, it indicates that tensile strain is generated in the growth plane. If the number of layer pairs is 9 or more, cracks are generated in the uppermost GaN single crystal layer 36, the strain is relaxed, and the c-axis lattice constant becomes equal to the bulk lattice constant. An increase in c-axis lattice constant (tensile strain) indicates a decrease in in-plane lattice constant (compressive strain), and an increase in c-axis lattice constant (tensile strain) indicates a decrease in in-plane lattice constant (compressive strain). Show.
The crystal strain is a relative name because the measured lattice constant value is referred to as tensile strain or compressive strain depending on the magnitude of the lattice constant compared to the bulk lattice constant. When the bulk lattice constants are found to have different values, the designation may change even with the same crystal strain.
The tensile strain at which cracks occur can be predicted by determining the corresponding critical lattice constant value.
[0023]
Here, when the crystal strain of the single crystal layer of one layer pair changes quantitatively in the single crystal layer of the second layer pair, it is referred to as “transition of crystal strain”. That is, the lattice constant has changed.
When the crystal strain of the single crystal layer of one layer pair is the tensile strain and the crystal strain of the second layer pair is a larger tensile strain, it is said that the crystal strain has “shifted to the tensile side”. That is, it means that the lattice constant has changed so as to increase.
When the crystal strain of the single crystal layer of one layer pair is the tensile strain and the crystal strain of the second layer pair is a smaller tensile strain, it is said that the crystal strain has “shifted to the compression side”. That is, it means that the lattice constant is changed so as to be small.
When the crystal strain of the single crystal layer of one layer pair is the tensile strain and the crystal strain of the second layer pair is the compressive strain, it is said that the crystal strain has “shifted to the compression side”. That is, it means that the lattice constant is changed so as to be small.
Even when a single crystal layer of one layer pair has a compressive strain, it is referred to as “transition to the compression side” and “transition to the tension side” as described above.
[0024]
The uppermost GaN single crystal layer 16 was cut and thinned to observe and count threading dislocations with a transmission electron microscope, and the crystal dislocation density, which is the density, was measured.
In FIG. 6, the change in crystal dislocation density on the surface of the uppermost GaN single crystal layer 16 with respect to the number of layer pairs is plotted as curve 1. The horizontal axis of the graph of FIG. 6 is the logarithm of the layer, and the vertical axis is the crystal dislocation density in units of square cm (cm−2) per unit from 1 × 10 7 cm −2 (1E7) to 1 × 1010 cm −2 (1E10). It is a scale. As the number of layer pairs increases, the crystal dislocation density decreases monotonously.
It should be noted that the etch pit density measured and reported by Akasaki et al. In JP-A-9-199759 differs from the crystal dislocation density here.
[0025]
“Experiment 2”:
A multilayer deposition substrate 30 shown in FIG. 3 where the number of layer pairs is 2 was formed from a substrate 32 similar to the substrate 12. Therefore, “Experiment 2” was performed by changing Step 3 of “Experiment 1” to Step 3 m in order to form the AlN low temperature deposition buffer layer 34.
Step 3m:
(Formation of the AlN low temperature deposition buffer layer 34): Thereafter, the temperature of the sapphire substrate 32 is set to 500 ° C., TMAl (trimethylaluminum) and ammonia are supplied into the furnace for about 3 minutes, and the AlN low temperature of 30 nm is formed on the sapphire substrate 32. A deposition buffer layer 34 is grown.
[0026]
4A to 4E are observation results of the surface of the uppermost GaN single crystal layer 36 when the number of layer pairs is 2, 3, 6, 9, and 12, respectively, using a differential interference microscope. In either case, no cracks are observed. Also, in FIG. 5, changes in the c-axis lattice constant of the surface of the uppermost GaN single crystal layer 16 when the number of layer pairs is 2, 3, 6, 9, 12 are plotted as curve 2. The lattice constant is constant at about 0.5188 nm and is larger than the bulk lattice constant of about 0.5185 nm. This indicates that compressive strain is generated in the growth surface direction of the uppermost GaN single crystal layer 16.
In FIG. 6, the change in the crystal dislocation density on the surface of the uppermost GaN single crystal layer 36 with respect to the number of layer pairs is plotted as curve 2. Also in “Experiment 2”, the crystal dislocation density decreases as the number of layer pairs increases.
[0027]
“Experiment 3”:
As shown in FIG. 7, three pairs of a GaN low temperature deposition buffer layer 54 and a GaN single crystal layer 56 are grown on a substrate 52 similar to the substrate 12 using Step 1 to Step 5 of “Experiment 1”. Thereafter, a pair of AlN low-temperature deposition buffer layer 55 and GaN single crystal layer 56 was grown in Step 3m of “Experiment 2” and Step 4 of “Experiment 1” to form a multilayer deposition substrate 50.
[0028]
FIG. 8 shows the result of observation of the surface of the uppermost GaN single crystal layer 56 by a differential interference microscope. The effect of the layer pair of the AlN low temperature deposition buffer layer 55 and the GaN single crystal layer 56 is that the c-axis lattice constant of the growth surface of the uppermost GaN single crystal layer 56 returns to 0.5188 nm and the crystal dislocation density decreases. is there.
Further growth of the GaN low-temperature deposition buffer layer 54 and the GaN single crystal layer 56 on the multilayer deposition substrate 50 using Step 1 to Step 5 of “Experiment 1” further reduces the crystal dislocation density without cracks. It is also possible to obtain a multilayer deposited substrate.
[0029]
"Discussion":
Therefore, as pointed out by Nakamura in Japanese Patent Laid-Open No. 4-297023, “(2) Since the buffer layer is GaN, when an epitaxial growth layer of GaN is grown thereon, the same material is grown on the same material. As can be seen from “Experiment 1”, the multilayer deposited substrate 10 has an upper limit in the number of layer pairs due to the occurrence of cracks. The upper limit can be taken to be modest and 6 at most. It can be seen that even four pairs or more, which were not clear in the prior art, can be deposited without cracking up to the upper limit. In addition, as seen in FIG. 6, Nakamura's indication was not verified with a layer pair number of 1.
Further, it can be seen that even if the buffer layer is not GaN, the number of layer pairs can be increased to reduce crystal defects.
[0030]
In addition, when the number of layer pairs is 2 or more, the average rate of decrease in crystal dislocation density with respect to the number of layer pairs is the same in both the GaN low temperature deposition buffer layer and the AlN low temperature deposition buffer layer. It is preferable that the resistance can be reduced and that there is no Al consumption. Therefore, only the uppermost layer pair has an AlN low temperature deposition buffer layer, or an AlN low temperature deposition buffer layer with an AlN molar fraction of 5% to 90%, preferably 10% to 50%, instead of the AlN low temperature buffer layer. This configuration is advantageous in that a request for reducing the resistance of the layer pair and a request for increasing the strain transfer to the tensile strain side can be arranged. Furthermore, the uppermost layer pair does not necessarily have to have a compressive strain in the growth plane, and the layer pair may be selected in a range in which no crack occurs in the uppermost single crystal layer according to the use of the deposited multilayer substrate.
Since the starting substrate can be grown not only on the sapphire substrate but also on a SiC, Si, MgAl2O4 substrate, an AlGaN thin film, or a substrate, device characteristics and cost can be arranged.
[0031]
Therefore, in order to increase the number of layer pairs to be deposited and reduce the crystal dislocation density, select layer pairs that do not generate cracks, or introduce layer pairs that generate compressive strain or reduce tensile strain before cracks occur. It can be said that the method of doing this and the multilayer deposition substrate constructed in this way are based on the present invention.
[0032]
As shown in FIG. 5, it is also known that the dislocation density decreases as the number of buffer layers increases as long as cracks do not occur. As described above, by selecting the material of the low temperature deposition buffer layer to be used, the number of layers can be arbitrarily selected without generation of cracks, that is, a substrate having an arbitrary dislocation density can be obtained.
[0033]
“Another Example of Experiment”
By the way, the patent application filed on October 16, 1998 by the applicant of the present application: Inventions of Takeuchi et al. (Hereinafter referred to as “the inventors of the present invention” described in the specification of “nitride semiconductor laser device”). "Invention of Takeuchi et al.") Deposited an AlN low temperature deposition buffer layer, an n-type GaN layer, an AlGaN low temperature deposition buffer layer, and an n-type AlGaN cladding layer on a sapphire substrate with a (0001) C plane. Thus, a nitride semiconductor laser element is configured.
Various experiments and considerations were made based on the invention of Takeuchi et al.
[0034]
(doping)
Doping is advantageous to reduce the resistivity of each layer pair. Furthermore, if the same kind of dopant is doped in the low temperature deposition buffer layer and the nitride semiconductor single crystal layer, the resistivity related to the low temperature deposition buffer layer can be reduced.
In many cases, it is preferable to perform more doping in the low temperature deposition buffer layer to promote a decrease in resistivity of the low temperature deposition buffer layer.
Si, Ge, and the like are used as n-type dopants, and Mg, Zn, and Be are used as p-type dopants. In particular, Si and Mg are preferable because the effect of lowering resistance and technically mature techniques can be applied. Choosing a high Si concentration lowers the resistivity of the n-type GaN layer but degrades the crystallinity. In addition, as in the case of Si, if the Mg concentration is too high, the crystallinity may be deteriorated, so care must be taken.
[0035]
In order to form the n-type AlN low temperature deposition buffer layers 34 and 55, Si is doped in the range of about 5 × 1017 to 5 × 1019 cm−3 by supplying silane simultaneously with TMAl (trimethylaluminum) and ammonium in the above step 3m. Good. In one example, it is 5 × 10 18 cm −3.
In the growth of the n-type GaN single crystal layers 16, 36, 56 and the n-type GaN low temperature deposition buffer layers 14, 54, Si is doped by supplying silane simultaneously with TMGa (trimethylgallium) and ammonia in Step 4 and Step 3 above. To do. The concentration is selected in the range of 5 × 10 17 cm −3 to 1 × 10 19 cm −3 with 2 × 10 18 cm −3 as the center. In one example, the concentration of dopant Si is 2 × 10 18 cm −3.
[0036]
Further, in the formation of the p-type AlN low temperature deposition buffer layers 34 and 55, TMAl (trimethylaluminum), ammonium and Cp2Mg (biscyclopentadienylmagnesium) are supplied at the same time in step 3m, so that Mg has a concentration of 1 × 10 18 to 5 × 10 20 cm −3. Dope within the range. In most cases, it is preferably about 1 × 1020 cm−3. As in the case of Si, care must be taken because the crystallinity can be degraded if the Mg concentration is too high.
The growth of the p-type GaN single crystal layers 16, 36, 56 and the p-type GaN low temperature deposition buffer layers 14, 54 is carried out in the above Step 4 and Step 3 with TMGa (trimethyl gallium) and ammonia together with Cp 2 Mg (biscyclopentadienyl magnesium). ) To be doped with Mg in a concentration range of 1 × 1018 to 1 × 1020 cm−3. On the other hand, it is preferably about 5 × 10 19 cm −3.
[0037]
(Composition and film thickness of low temperature deposition buffer layer or single crystal layer)
It has been found that the composition of the low temperature deposition buffer layer constituting the layer pair may be an AlGaN ternary compound in order to introduce the compressive strain, and may be an AlN molar fraction of 5% or more, preferably 10% or more. For applications where the resistivity of the low temperature deposition buffer layer is desired to be kept small, the AlN mole fraction should be selected to be less than 50% and, if the resistivity is quite important, about 10%.
The film thickness of the low-temperature deposited buffer layer is not less than a predetermined value at which the buffer effect is stably obtained, and not more than another predetermined value so that the crystal quality of itself and the nitride semiconductor single crystal layer are kept good. There is this like this. Therefore, the film thickness is preferably 2 nm or more and 100 nm or less, and more preferably 10 nm to 50 nm. The deposition temperature is selected in the range of 300 ° C to 700 ° C.
[0038]
The single crystal layer is not limited to the GaN layer but may be an AlGaN ternary compound layer. In the invention of Takeuchi et al., A single crystal layer of the AlGaN ternary compound is deposited on the low temperature deposition buffer layer of the AlGaN ternary compound.
The film thickness of the single crystal layer is preferably in the range of 0.1 μm to 3 μm. If it is thin, the production time is short, which is advantageous, but if it is too thin, the crystallinity deteriorates. The growth temperature is selected in the range of 1000 ° C to 1200 ° C.
[0039]
(Growth method)
In the above experimental examples, the MOVPE (metal organic vapor phase epitaxy) apparatus was used exclusively. Although it seems that there is no difficulty in making the present invention with other apparatuses, it is preferable to use a MOVPE (metal organic vapor phase epitaxy) apparatus in view of the maturity of the technology, operability, and cost.
[0040]
(Ease of manufacturing)
Since the tensile strain and the compressive strain can be observed at least by measuring the lattice constant at room temperature, it is possible to measure the lattice constant when performing a sampling inspection during mass production, so that the stability of the manufacturing process can be measured in a short time. Contributes to cost reduction.
[0041]
【The invention's effect】
By implementing the present invention, a multilayer substrate with few lattice defects can be formed, so that not only an optical element such as a laser diode but also an element structure and characteristics using many group III nitride semiconductors can be improved.
Non-limiting examples of these devices include AlGaN / GaN modulation-doped field effect transistors, ridge waveguide laser diodes, pn junction PDs (photodetection diodes), AlN / GaN semiconductor multi-thick reflective films, and AlN / GaN sub-layers. For example, an interband transition device.
[Brief description of the drawings]
FIG. 1 is a structural diagram of a multilayer deposition substrate 10 in which two pairs of layers composed of a GaN low temperature deposition buffer layer and a GaN single crystal layer are deposited on a sapphire substrate.
FIG. 2 is a differential interference microscope photograph of the surface of the uppermost GaN single crystal layer of a multilayer deposition substrate in which a layer pair consisting of a GaN low temperature deposition buffer layer and a GaN single crystal layer is deposited on a sapphire substrate.
FIG. 3 is a structural diagram of a multilayer deposition substrate 30 in which two pairs of layer pairs composed of an AlN low temperature deposition buffer layer and a GaN single crystal layer are deposited on a sapphire substrate.
FIG. 4 is a photograph taken by a differential interference microscope of the surface of the uppermost GaN single crystal layer of a multilayer deposition substrate in which a layer pair consisting of an AlN low temperature deposition buffer layer and a GaN single crystal layer is deposited on a sapphire substrate.
FIG. 5 is a graph showing changes in the lattice constant of the c-axis on the surface of the uppermost GaN single crystal layer with respect to the number of layer pairs of the multilayer deposition substrate.
FIG. 6 is a graph showing a change in lattice dislocation density on the surface of the uppermost GaN single crystal layer with respect to the number of layer pairs of the multilayer deposition substrate.
FIG. 7 shows a multilayer formed by growing three pairs of a GaN low temperature deposition buffer layer and a GaN single crystal layer on a sapphire substrate and then growing a pair of AlN low temperature deposition buffer layer and a GaN single crystal layer pair. 3 is a structural diagram of a deposition substrate 50. FIG.
8 is a photograph of the surface of the uppermost GaN single crystal layer of the multilayer deposition substrate 50 of FIG. 7 using a differential interference microscope.
[Explanation of symbols]
10, 30, 50 multilayer deposition substrate,
12, 32, 52 Sapphire substrate 14, 54 GaN low temperature deposition buffer layer 16, 36, 56 GaN single crystal layer 34, 55 AlN low temperature deposition buffer layer

Claims (19)

A substrate made of a first material;
A stacked layer pair located on the substrate,
The layer pair is
A buffer layer made of a low temperature deposited nitride semiconductor;
A single crystal layer of single crystal GaN grown directly on the buffer layer,
The at least one layer pair, the buffer layer of which consists of AlGaN or AlN, is located above the at least one layer pair, of which the buffer layer is made of AlGaN or AlN, and the other layer pair of which the buffer layer is made of GaN. A nitride semiconductor multilayer deposition substrate, wherein the in-plane strain of the crystal layer is configured to have the in-plane strain of a single crystal layer which is a compressive strain. The nitride semiconductor multilayer deposition substrate according to claim 1, wherein the stack includes three layer pairs. The nitride semiconductor multilayer deposition substrate according to claim 1, wherein the stack includes four layer pairs. 4. The buffer layer according to claim 1, wherein the buffer layer in the at least one layer pair made of AlGaN or AlN is made of AlGaN having an AlN molar fraction of between 5% and 100%. The nitride semiconductor multilayer deposition substrate according to claim. 5. The nitride semiconductor multilayer deposition substrate according to claim 4, wherein the buffer layer of the other layer pair is made of GaN. 6. The nitride semiconductor multilayer deposition substrate according to claim 5, wherein the number of adjacent layer pairs having a buffer layer made of GaN is less than six. 4. The nitride semiconductor multilayer deposition according to claim 1, wherein a majority of the buffer layer of the layer pair is made of AlGaN having an AlN mole fraction of between 10% and 90%. 5. substrate. The nitride semiconductor multilayer deposition substrate according to claim 4, wherein the AlN molar fraction is between 10% and 50%. 9. The nitride semiconductor multilayer deposition substrate according to claim 8, wherein the AlN molar fraction is approximately 10%. A method of forming a multi-layer deposition substrate comprising:
Providing a substrate of a first material;
Forming a stacked layer pair on the substrate,
Each of the layer pairs is
Depositing a low temperature deposited nitride semiconductor buffer layer at a temperature below that at which single crystal growth occurs;
Growing a single crystal layer of single crystal GaN directly on the buffer layer,
In the case of forming the layer pair of the stacked layers, the in-plane strain of the single crystal layer of the other layer pair in which the buffer layer is made of GaN, on which at least one layer pair of the buffer layer is made of AlGaN or AlN is positioned. Forming a single crystal layer that has compressive strain so as to have an in-plane strain, and forming a nitride semiconductor multilayer deposition substrate. The method for forming a nitride semiconductor multilayer deposition substrate according to claim 10, wherein in forming the stack, a stack having three layer pairs is formed. The method for forming a nitride semiconductor multilayer deposition substrate according to claim 10, wherein in forming the stack, a stack having four layer pairs is formed. In forming the buffer layer, a layer made of a semiconductor material composed of AlGaN having an AlN molar fraction of 5% to 100% is used as the buffer layer in at least one layer pair in which the buffer layer is composed of AlGaN or AlN. 13. The method for forming a nitride semiconductor multilayer deposition substrate according to claim 10, wherein the nitride semiconductor multilayer deposition substrate is deposited. 14. The method for forming a nitride semiconductor multilayer deposition substrate according to claim 13, wherein in forming the buffer layer, layers made of a semiconductor material made of GaN are each deposited as a buffer layer of another layer pair. 15. The nitride semiconductor multilayer according to claim 14, wherein in forming the stack, the stack is formed such that the number of adjacent layer pairs having a buffer layer made of GaN is less than six. Method for forming a deposition substrate. A semiconductor layer composed of AlGaN having an AlN mole fraction between 10% and 90% is deposited as a buffer layer of a majority of the layer pairs in depositing the buffer layer. 14. A method for forming a nitride semiconductor multilayer deposition substrate according to 13. The method for forming a nitride semiconductor multilayer deposition substrate according to any one of claims 13 to 16, wherein an AlN molar fraction is between 10% and 50% in depositing the buffer layer. The method for forming a nitride semiconductor multilayer deposition substrate according to any one of claims 13 to 16, wherein an AlN molar fraction is approximately 10% for depositing the buffer layer. The method further comprises the step of measuring the lattice constant of the single crystal layer at one of room temperature (a) and elevated temperature (b) to determine in-plane strain of the single crystal layer. The method for forming a nitride semiconductor multilayer deposition substrate according to any one of 18.

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