KR101135950B1

KR101135950B1 - A semiconductor and a fabrication method thereof

Info

Publication number: KR101135950B1
Application number: KR20090113277A
Authority: KR
Inventors: 서용곤; 황성민
Original assignee: 전자부품연구원
Priority date: 2009-11-23
Filing date: 2009-11-23
Publication date: 2012-04-18
Also published as: KR20110056805A

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method of manufacturing the same. The present invention relates to a semiconductor device comprising: a substrate having a hexagonal crystal structure; A buffer layer grown on the main surface of the substrate with the a-plane ({11-20} plane) as a main surface in a horizontal growth mode; A first semiconductor layer grown on the main surface of the buffer layer with a-plane ({11-20} plane) as a main surface in a vertical growth mode; And a second semiconductor layer grown on the main surface of the first semiconductor layer with the a-plane ({11-20} plane) as the main surface in a horizontal growth mode. to provide.

Hexagonal System, Group III, Group V

Description

A semiconductor device and method for manufacturing the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method for manufacturing the same, and more particularly, to a semiconductor device and a method for manufacturing the same, which are made of Group III-V compounds produced in high quality in a horizontal growth mode in an inert gas atmosphere.

In general, the semiconductor light emitting device may be a light emitting diode (LED). LEDs are devices used to send and receive signals by converting electrical signals into infrared, visible or light using the properties of compound semiconductors.

The use range of LED is used in home appliances, remote controllers, electronic signs, indicators, and various automation devices, and the types are largely divided into Infrared Emitting Diode (IRD) and Visible Light Emitting Diode (VLED).

As the usage area of LEDs becomes wider, the required luminance, such as electric lamps used for living and electric lamps for rescue signals, becomes higher and higher, and in recent years, development of high-power light emitting diodes is actively underway.

In particular, much research and investment have been made on semiconductor optical devices using Group III and Group V compounds such as GaN (gallium nitride), AlN (aluminum nitride), InN (indium nitride), and the like. This is because the nitride semiconductor light emitting device has a bandgap of a very wide area ranging from 1.9 eV to 6.2 eV, and thus has three advantages of realizing three primary colors of light.

As such, nitride-based single crystal substrates such as gallium nitride (GaN), which are used as main substrates in the manufacture of semiconductor devices, are mostly nitride films of c-plane ({0001} plane), mainly sapphire c-plane ({0001}). Cotton) It is obtained by growing on a single crystal substrate by the method of Metal Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE) or HVPE. As described above, in the c-plane ({0001} plane) nitride-based single crystal film thus formed, the gallium layer and the nitrogen layer are repeatedly stacked in the c-crystal axial direction, thereby exhibiting polarity.

For example, for GaN / AlGaN heterostructures, the electronic band structure within the heterostructure is tilted by a strong electric field formed by spontaneous polarization or piezoelectric polarization. Reduce the carrier recombination rate, resulting in lower quantum efficiency.

In detail, there is a polarization discontinuity in the c-crystal growth direction, creating a sheet charge fixed to the surface and interface, resulting in an internal electric field in the quantum well. The separation of the electron and hole wave functions to shift the light emission toward the red wavelength, and when the electric field is applied, the emission wavelength is shifted toward the short wavelength, making it difficult to develop a device for long wavelength.

In contrast, since a-plane ({11-20}) nitride-based crystals have non-polar characteristics, the problem of c-plane ({0001}) nitride-based single crystals as described above, namely, polarization It is possible to overcome the problem that the quantum efficiency is reduced by the internal electric field by.

The a-plane ({11-20}) nitride-based crystals do not have a polarization field and thus do not cause band bending, and have a stark effect from a structure in which an AlGaN / GaN quantum well is grown on a non-polar crystal plane. Since no effect) is observed, the non-polar nitride-based heterostructure on the a-plane ({11-20} plane) has the potential to be usefully used for high-efficiency ultraviolet light-emitting elements and high-power microwave transistors.

In addition, the a-plane ({11-20} plane) nitride film may have a higher concentration of p-doping than the c-plane ({0001} plane) nitride single crystal film. This is because the activation energy is lower than the c-plane (the {0001} plane) on the a-plane ({11-20} plane). In addition, the more doped Al is included in GaN, the doping efficiency is generally reduced sharply, the doping is relatively higher in the a-plane ({11-20} plane) than the c-plane ({0001} plane).

Although the a-plane ({11-20} plane) nitride-based single crystal film has many advantages over the c-plane ({0001} plane), it has not been manufactured and commercialized as a substrate because it has good crystallinity. This is because it is difficult to obtain a smooth film surface.

As such, the reason why the growth on the a-plane ({11-20} plane) is difficult is that gallium and nitrogen coexist so that the growth rates of gallium and nitrogen are different.

Accordingly, an object of the present invention in view of the conventional requirements as described above is to improve the rough surface and low quality crystallinity due to the difference in growth rate of gallium and nitrogen in the manufacture of a semiconductor device having a nonpolarized or semipolarized buffer layer. A semiconductor device and a method of manufacturing the same are provided.

A semiconductor device according to a preferred embodiment of the present invention for achieving the above object is a substrate having a hexagonal crystal structure; A buffer layer grown on the main surface of the substrate with the a-plane ({11-20} plane) as a main surface in a horizontal growth mode; A first semiconductor layer grown on the main surface of the buffer layer with a-plane ({11-20} plane) as a main surface in a vertical growth mode; And a second semiconductor layer grown on the main surface of the first semiconductor layer with the a-plane ({11-20} plane) as the main surface in a horizontal growth mode.

The buffer layer and the second semiconductor layer are formed using an inert gas having low thermal conductivity as an atmosphere gas.

The inert gas is characterized in that any one selected from argon and nitrogen.

The buffer layer and the second semiconductor layer may be formed in a mixed atmosphere of an inert gas having low thermal conductivity and a gas having high thermal conductivity.

The inert gas having low thermal conductivity is any one selected from argon and nitrogen, and the high thermal conductivity gas is any one selected from hydrogen and helium.

The substrate has a r-plane ({1-102} plane) or an m-plane ({1-100} plane) of a hexagonal crystal structure as a main surface.

The buffer layer, the first semiconductor layer and the second semiconductor layer is formed from a III-V group compound.

The ratio of the Group V element (V / III) to the Group III element of the Group III-V compound forming the buffer layer and the second semiconductor layer is characterized in that 10 to 400.

The ratio of the Group V element (V / III) to the Group III element of the Group III-V compound forming the first semiconductor layer is characterized in that 800 to 1500.

The buffer layer, the first semiconductor layer and the second semiconductor layer is characterized by growing at a growth temperature of 900 to 1200 ℃.

The buffer layer and the second semiconductor layer is grown at a pressure of 50 to 200 mbar, the first semiconductor layer is characterized in that the growth at a pressure of 400 to 700 mbar.

The buffer layer is grown to a thickness of 5 to 300nm, the first semiconductor layer is characterized by growing to a thickness of 1 to 2μm, the second semiconductor layer is characterized by growing to a thickness of 1 to 10μm.

A method of manufacturing a semiconductor device according to an embodiment of the present invention for achieving the above object, the process of providing a substrate having a hexagonal crystal structure, and a-plane (in the horizontal growth mode on the main surface of the substrate) Growing the buffer layer with the {11-20} plane as the main plane, and growing the first semiconductor layer with the a-plane (the {11-20} plane) as the main plane in the vertical growth mode on the main plane of the buffer layer. And growing a second semiconductor layer on the main surface of the first semiconductor layer with the a-plane ({11-20} plane) as the main surface in a horizontal growth mode.

The buffer layer and the second semiconductor layer are formed in a mixed atmosphere of an inert gas having low thermal conductivity and a gas having high thermal conductivity.

The inert gas having low thermal conductivity is any one selected from argon and nitrogen, and the gas having high thermal conductivity is any one selected from hydrogen and helium.

The ratio of the Group V element (V /) III to the Group III element of the Group III-V compound forming the first semiconductor layer is characterized in that 800 to 1500.

According to the embodiment of the present invention as described above, the gallium nitride semiconductor is grown in an inert gas atmosphere having low thermal conductivity in the horizontal growth mode. The rough surface and low quality crystallinity due to the difference in the growth rate of gallium and nitrogen, according to the embodiment of the present invention can slow the growth of gallium as much as possible to reduce the difference in growth rate with nitrogen. Accordingly, a high quality a-plane ({11-20} plane) semiconductor layer can be obtained by improving the rough surface and low crystallinity.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. At this time, it should be noted that the same components in the accompanying drawings are represented by the same reference numerals as possible. In addition, detailed descriptions of well-known functions and configurations that may blur the gist of the present invention will be omitted.

Hereinafter, the semiconductor device and the method of manufacturing the same will be described with respect to the light emitting device and the method for manufacturing the same. In particular, in the horizontal growth mode of the buffer layer serving as a buffer of the upper and lower layers on the substrate, such as argon or nitrogen Provided is a method of growing a high quality Al _x Ga _(1-x) N (0≤x≤1) layer in an inert gas atmosphere having low thermal conductivity to improve its crystal and surface properties. In the embodiment of the present invention, a description will be given mainly of the nitride semiconductor, in particular, GaN, but is not limited to this, all nitride semiconductors such as Al _x Ga _(1-x) N (0≤x≤1) can be applied.

In an embodiment of the present invention, the "horizontal growth mode" means growing faster by growing sideways than growing upward. Correspondingly, " vertical growth mode " means to grow faster by growing faster than laterally growing.

1 and 2 are side cross-sectional views schematically showing a semiconductor device according to an embodiment of the present invention.

Referring to FIG. 1, a semiconductor device according to an embodiment of the inventive concept may include a substrate 100, a buffer layer 200, a first semiconductor layer 300, and a second semiconductor layer sequentially grown on the substrate 100. 400.

Also, referring to FIG. 2, the semiconductor device may include an n-type semiconductor layer 500 formed on the second semiconductor layer 400, an active layer 600 sequentially stacked on some surfaces of the n-type semiconductor layer 500, and The p-type semiconductor layer 700, the n-type electrode 800 formed on the surface on which the active layer 600 of the n-type semiconductor layer 500 is not stacked, and the p-type electrode 900 formed on the p-type semiconductor are further added. It may be a semiconductor light emitting device.

The substrate 100 uses the sapphire substrate 100, and uses the r-plane ({1-102} plane) or the m-plane ({1-100} plane) of a hexagonal crystal structure as its main surface.

The buffer layer 200, the first semiconductor layer 300, and the second semiconductor layer 400 may be formed using a group III-V compound, and the group III-V compound may include GaN, AlN, and InN. . In this case, in the group III-V compound forming the buffer layer 200 and the second semiconductor layer 400, the ratio of the group III element (V / III) to the group III element is preferably 10 to 400. Meanwhile, in the group III-V compound forming the first semiconductor layer 300, the ratio of group V elements (V / III) to the group III elements is preferably 800 to 1500.

The buffer layer 200, the first semiconductor layer 300, and the second semiconductor layer 400 are sequentially stacked on the substrate 100, and grow on the a-plane ({11-20} plane) as the main surface. Let's do it. In this case, the buffer layer 200 and the second semiconductor layer 400 grow in a horizontal growth mode, and the first semiconductor layer 300 grows in a vertical growth mode. When the buffer layer 200, the first semiconductor layer 300, and the second semiconductor layer 400 are all grown in a horizontal growth mode with the a-plane ({11-20} plane) as the main surface, the growth time is long. For this reason, the growth rate may be increased by growing the first semiconductor layer 300 in the vertical growth mode.

In particular, the buffer layer 200 is formed on the main surface of the substrate 100, the buffer layer 200 serves to buffer the stress between the substrate 100 and the layer 300 grown on the substrate 100. To perform.

Since the buffer layer 200 is formed on the a-plane ({11-20} plane) as the main plane, the non-polarization buffer layer 200 is formed when the substrate 100 is formed on the r-plane ({1-102} plane). You can get it. In addition, when the substrate 100 uses the m-plane ({1-100} plane) as the main plane, the semi-polarization buffer layer 200 can be obtained.

When the buffer layer 200 is grown on the c-plane ({0001} plane) on the substrate 100 according to the conventional art, the growth process is performed under a hydrogen atmosphere. On the other hand, according to the embodiment of the present invention, the buffer layer 200 and the second semiconductor layer 400 are grown by using an a-plane ({11-20} plane) as an inert gas having low thermal conductivity as an atmosphere gas. Such inert gases can exemplify argon or nitrogen. As such, when the inert gas having low thermal conductivity is used as the atmosphere gas, the buffer layer 200 may be uniformly formed as a whole by lowering the growth rate of gallium, which is faster than nitrogen. Accordingly, crystallinity and surface characteristics of the buffer layer 200 can be improved.

In addition, the buffer layer 200 and the second semiconductor layer 400 may be grown in an inert gas atmosphere having low thermal conductivity or a mixed atmosphere of an inert gas having low thermal conductivity and a gas having high thermal conductivity in the horizontal growth mode. Gas having high thermal conductivity may exemplify H ₂ or He. The atmosphere gas of the mixed atmosphere is preferably used when the second semiconductor layer 400 is grown or when the buffer layer 200 is grown on the m-plane ({1-100} plane) substrate 100. Do.

On the other hand, the first semiconductor layer 300 is formed using hydrogen as the atmosphere gas.

When the buffer layer 200, the first semiconductor layer 300, and the second semiconductor layer 400 are grown, they are grown at a growth temperature of 900 to 1200 ° C.

When the buffer layer 200 and the second semiconductor layer 400 are grown, the growth pressure is preferably set to 50 to 200 mbar, and the first semiconductor layer 300 is preferably grown by applying a pressure of 400 to 700 mbar. Do.

The buffer layer 200 may be grown to a thickness of 5 to 300 nm, the first semiconductor layer 300 may be grown to a thickness of 1 to 2 μm, and the second semiconductor layer 400 may be grown to a thickness of 1 to 10 μm. .

Next, a semiconductor device manufacturing method according to an embodiment of the present invention will be described. 3 is a flowchart illustrating a method of fabricating a semiconductor device in accordance with an embodiment of the present invention, and FIGS. 4 to 8 are side cross-sectional views illustrating a method of fabricating a semiconductor device in accordance with an embodiment of the present invention.

Referring to FIG. 3, the substrate 100 is prepared in step S210. Here, the sapphire substrate 100 is preferably the substrate 100. In particular, the substrate 100 is preferably formed such that the r-plane ({1-102} plane) faces the main plane, that is, the r-plane ({1-102} plane) faces upward. In addition, the board | substrate 100 can make m-plane ({1-100} surface) into a main surface, without making r-plane ({1-102} plane) into a main surface. This substrate 100 is shown in FIG. 4.

Next, referring to FIG. 5, the buffer layer 200 is formed in the horizontal growth mode in step S220 on the r-plane ({1-102} plane) of the substrate 100 described above. At this time, it is preferable to grow GaN having the a-plane ({11-20} plane) as a main surface on the r-plane ({1-102} plane) of the substrate 100 as the buffer layer 200.

While the growth of the buffer layer 200 mainly having a c-plane ({0001} plane) is performed under a hydrogen atmosphere, in the present invention, an inert gas having low thermal conductivity is used as the atmosphere gas to form the buffer layer 200. Such inert gases can exemplify argon or nitrogen. As such, when the inert gas having low thermal conductivity is used as the atmosphere gas, the buffer layer 200 may be uniformly formed as a whole by lowering the growth rate of gallium, which is faster than nitrogen. At this time, the buffer layer 200 is grown at a temperature of 900 to 1200 ℃.

In addition, the buffer layer 200 may be formed using a III-V compound as a material for forming the buffer layer 200, and typically, the III-V compound may be GaN. In addition, other Group III-V compounds such as AlN and InN may be used instead of GaN. In this case, the ratio of the Group V element (V / III) to the Group III element is preferably 10 to 400.

In addition, the buffer layer 200 is preferably formed at a growth pressure of 50 to 200 mbar during growth, and the thickness is preferably grown to 5 to 300 nm.

On the other hand, when the substrate 100 uses the sapphire substrate 100 having the m-plane ({1-100} plane) as the main surface instead of the r-plane ({1-102} plane) as the main surface, the substrate 100 By growing GaN having the a-plane ({11-20} plane) as the main surface on the N-side, GaN of the semi-polarization 11-22 can be obtained. In this case, the buffer layer 200 may be grown in an inert gas atmosphere having low thermal conductivity or a mixed atmosphere of inert gas having low thermal conductivity and gas having high thermal conductivity in the horizontal growth mode in which the buffer layer 200 is formed. Gas having high thermal conductivity may exemplify H ₂ or He.

Referring to FIG. 6, growth of the a-plane ({11-20} plane) GaN, which is the buffer layer 200 in the horizontal growth mode as a whole, takes a long time to grow, and thus, in the vertical growth mode on the buffer layer 200 in step S230. The first semiconductor layer 300 is formed. The first semiconductor layer 300 grows a-plane ({11-20} plane) GaN and may increase the growth rate by growing in a vertical growth mode.

The first semiconductor layer 300 is formed using hydrogen as an atmosphere gas. At this time, the first semiconductor layer 300 is formed at a temperature of 900 to 1200 ℃.

The first semiconductor layer 300 may be formed using a III-V compound, and typically, the III-V compound may be GaN. At this time, the ratio of the Group V element (V / III) to the Group III element is preferably 800 to 1500.

The first semiconductor layer 300 is preferably grown at a growth pressure of 400 to 700 mbar, and preferably at a thickness of 1 to 2 μm.

Referring to FIG. 7, in operation S240, the second semiconductor layer 400 is formed on the first semiconductor layer 300 in a horizontal growth mode. The second semiconductor layer 400 preferably grows a-plane ({11-20} plane) GaN, thereby improving crystallinity and surface properties. The second semiconductor layer 400 grows to a thickness of 1 to 10 μm.

The growth conditions of the second semiconductor layer 400 are performed within the same range as that of the buffer layer 200. That is, the buffer layer 200 is formed using an inert gas such as argon or nitrogen having low thermal conductivity as an atmosphere gas. As such, when the inert gas having low thermal conductivity is used as the atmosphere gas, the buffer layer 200 may be uniformly formed as a whole by lowering the growth rate of gallium, which is faster than nitrogen.

When the second semiconductor layer 400 is formed in the horizontal growth mode, the second semiconductor layer 400 may be grown in a mixed atmosphere of an inert gas having a low thermal conductivity and a gas having a high thermal conductivity instead of an inert gas atmosphere having a low thermal conductivity. Here, the gas having high thermal conductivity may exemplify H ₂ or He.

The second semiconductor layer 400 is grown at a temperature of 900 to 1200 ° C. In addition, the second semiconductor layer 400 uses a III-V compound as its material, and the ratio of the Group V element (V / III) to the Group III element is preferably 10 to 400. The second semiconductor layer 400 is preferably formed with a growth pressure of 50 to 200 mbar during its growth.

Referring to FIG. 8, as described above, after manufacturing the substrate 100 according to the embodiment of the present invention, the n-type semiconductor layer 500 is formed on the second semiconductor layer 400 in step S250. . Next, the active layer 600 is stacked on the n-type semiconductor layer 500 in step S260, and the p-type semiconductor layer 700 is formed on the active layer 600 in step S270.

The n-type semiconductor layer 500 is preferably doped with Si (silicon), and the p-type semiconductor layer 700 is doped with Mg (magnesium).

Here, the active layer 600 has a quantum well (MQW) structure and generates light by combining holes flowing through the p-type semiconductor layer 700 and electrons flowing through the n-type semiconductor layer 500. At this time, light of energy corresponding to the excitation level or the energy band gap difference of the quantum well is emitted.

Then, the active layer 600 and a portion of the p-type semiconductor layer 700 is removed to expose a portion of the top surface of the n-type semiconductor layer 500 in step S280.

Next, the n-type electrode 800 is formed on the n-type semiconductor layer 500 exposed in step S290, and the p-type electrode 900 is formed on the p-type semiconductor layer 700 in step S300. To complete.

9 and 10 are views for explaining the effect of the semiconductor device manufacturing method according to an embodiment of the present invention.

FIG. 9 illustrates a- grown on the sapphire substrate 100 having the r-plane ({1-102} plane) as growth conditions of the buffer layer 200 having the general c-plane ({0001} plane) as the main plane. The surface of the buffer layer 200 mainly having a plane ({11-20} plane) is illustrated, and FIG. 10 shows a plane ({11-20} plane) grown under growth conditions according to an embodiment of the present invention. The buffer layer 200 surface is shown. Here, the buffer layer 200 was grown using GaN as a material.

As shown, the buffer layer 200 whose main surface is the a-plane ({11-20} plane) formed under the c-plane ({0001} plane) growth conditions has a very rough surface, whereas in the embodiment of the present invention, It can be seen that the buffer layer 200 whose main surface is the a-plane ({11-20} plane) accordingly can obtain a very clean surface.

11 is a graph for explaining the effect of the semiconductor device manufacturing method according to an embodiment of the present invention.

In FIG. 11, the buffer layer 200 is phi-scanned by x-ray to compare crystallinity.

The graph of FIG. 11 shows a scan result 51 of the buffer layer 200 grown under growth conditions having a general c-plane ({0001} plane) as a main surface, and a- grown with growth conditions according to an embodiment of the present invention. The scan result 53 of the buffer layer 200 whose plane ({11-20} plane) is the main plane is shown.

As shown, when the c-axis direction of the hexagonal system was measured based on the reference (0 ^o ), the x-ray half width was 1445 arcsec in the existing c-plane ({0001} plane) growth conditions. Under the conditions of 349 arcsec, the crystallinity was found to be very good.

As described above, according to the exemplary embodiment of the present invention, by growing a gallium nitride semiconductor using an inert gas having low thermal conductivity as an atmosphere gas in a horizontal growth mode, the growth rate with respect to nitrogen may be reduced by delaying the growth of gallium as much as possible. As a result, it is possible to improve the rough surface due to the difference in the growth rate of gallium and nitrogen and the crystallinity of low quality, and to obtain a semiconductor layer made of GaN of high quality as a whole.

On the other hand, the embodiments of the present invention disclosed in the specification and drawings are merely presented specific examples to easily explain the technical contents of the present invention and help the understanding of the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein.

1 and 2 are side cross-sectional views schematically showing the components of a semiconductor device according to an embodiment of the present invention.

3 is a flowchart illustrating a method of fabricating a semiconductor device in accordance with an embodiment of the present invention.

4 to 8 are side cross-sectional views illustrating a method of fabricating a semiconductor device in accordance with an embodiment of the present invention.

Claims

In the manufacturing method of a semiconductor device using a III-V group compound,

Preparing a substrate having a hexagonal crystal structure,

A-plane ({11-) on the main surface of the substrate in a horizontal growth mode in which a group III-V compound is supplied at 900 to 1200 ° C, 50 to 200 mbar, and a V / III ratio of 10 to 400 in an argon or nitrogen gas atmosphere. 20} cotton) as a main surface to grow a buffer layer,

Growing a first semiconductor layer on the main surface of the buffer layer with the a-plane ({11-20} plane) as a main surface in a vertical growth mode;

And growing a second semiconductor layer on the main surface of the first semiconductor layer in a horizontal growth mode with the a-plane ({11-20} plane) as the main surface.

The method of claim 1,

And the second semiconductor layer is grown in an argon gas or nitrogen gas atmosphere.

The method of claim 1,

And the second semiconductor layer is grown by using a mixture of one selected from argon gas and nitrogen gas and one selected from hydrogen gas and helium gas as an atmosphere gas.

The method of claim 1,

The substrate has a r-plane ({1-102} plane) or m-plane ({1-100} plane) of a hexagonal crystal structure as a main surface.

The method of claim 1,

The method of manufacturing a semiconductor device, characterized in that the ratio of the Group V element (V / III) to the Group III element of the Group III-V compound to grow the second semiconductor layer.

The method of claim 1,

The method of manufacturing a semiconductor device, characterized in that the ratio of the Group V element (V / III) to the Group III element of the Group III-V compound to grow the first semiconductor layer.

The method of claim 1,

And the first semiconductor layer is grown in a hydrogen gas atmosphere.

The method of claim 1,

And the first semiconductor layer and the second semiconductor layer are grown at a growth temperature of 900 to 1200 ° C.

The method of claim 1,

Wherein the second semiconductor layer is grown at a pressure of 50 to 200 mbar, and the first semiconductor layer is grown at a pressure of 400 to 700 mbar.

The method of claim 1,

Wherein the buffer layer is grown to a thickness of 5 to 300 nm, the first semiconductor layer is grown to a thickness of 1 to 2 μm, and the second semiconductor layer is grown to a thickness of 1 to 10 μm. .

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