JP2009170542A - Epitaxial-wafer manufacturing method and epitaxial wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method to manufacture an epitaxial wafer for a nitride semiconductor light-emitting element, capable of generating long-wavelength light, while avoiding the occurrence of droplets. <P>SOLUTION: In the method to manufacture an epitaxial wafer for a nitride semiconductor light-emitting element, an Al<SB>X2</SB>Ga<SB>1-X2</SB>N (0≤X2≤1) layer 19 is grown on a substrate 11, having the surface made of In<SB>X1</SB>Ga<SB>1-X1</SB>N (0<X1≤1), at a first temperature T1. A GaN layer 23 is grown on the Al<SB>X2</SB>Ga<SB>1-X2</SB>N layer 19 at a second temperature T2. The Al<SB>X2</SB>Ga<SB>1-X2</SB>N layer 19 covers the surface of the substrate 11. The growth temperature (T1) of the Al<SB>X2</SB>Ga<SB>1-X2</SB>N (0≤X2≤1) layer 19 is lower than the growth temperature (T2) of the GaN layer 23. The substrate 11 may be an InGaN template or an InGaN bulk substrate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an epitaxial wafer and an epitaxial wafer.

Patent Document 1 describes a short wavelength semiconductor light emitting device that exhibits high reliability even under high output oscillation and realizes a long wavelength up to about 550 nm. In order to form this semiconductor light emitting device, a GaN buffer layer having a thickness of about 20 nm is formed on a C-plane sapphire substrate, and then a GaN layer having a thickness of about 2 μm is grown. A patterned SiO ₂ layer is formed on the GaN layer. Thereafter, InGaN having a thickness of about 20 μm is selectively grown.
JP 2000-299530 A

  According to the knowledge of the inventors, it has become possible to grow InGaN and InN by the HVPE method having a high growth rate, and a bulk substrate made of InGaN or InN or a template made of InGaN or InN can be used. It has become like this.

In Patent Document 1, InGaN is grown laterally using a SiO ₂ mask formed on GaN in order to reduce distortion of the InGaN layer. However, the production of the SiO ₂ mask is complicated. If the above-described bulk substrate or template is used, photolithography for creating a mask as in Patent Document 1 is not necessary.

  When using a bulk substrate or template, high-temperature-grown GaN with good crystallinity is desirable for the initial layer of epitaxial growth. However, when GaN is deposited, InGaN (InN) on the bulk substrate surface and the template surface decomposes during the temperature rise to the growth temperature of GaN, and droplets are generated on the bulk substrate and the template.

  By using an InGaN (InN) -based semiconductor, a nitride-based semiconductor light-emitting element capable of generating long-wavelength light is provided. Therefore, it is desired to avoid the generation of droplets for this production.

  The present invention has been made in view of such circumstances, and is an epitaxial for a nitride-based semiconductor light-emitting device capable of generating light having a long wavelength while avoiding generation of droplets due to InGaN (InN). It is an object of the present invention to provide a method for producing a wafer and to provide this epitaxial wafer.

One aspect of the present invention is a method of fabricating an epitaxial wafer for a nitride based semiconductor light emitting device. In this method, (a) an Al _X2 Ga _1-X2 N (0 ≦ X2 ≦ 1) layer is formed at a first temperature on a substrate having a surface made of In _X1 Ga _1-X1 N (0 <X1 ≦ 1). And (b) growing a GaN layer on the Al _X2 Ga _1-X2 N layer at a second temperature. The Al _X2 Ga _1-X2 N layer covers the surface of the substrate, and the first temperature is lower than the second temperature.

According to the present invention, before the GaN layer of good crystal quality is grown at a high temperature, the Al _X2 Ga _1-X2 N layer is grown at a low temperature to cover the In _X1 Ga _1-X1 N surface. Therefore, even in a high temperature atmosphere related to the growth of the GaN layer, decomposition of In _X1 Ga _{1 -X1} N can be avoided, and no droplets are generated. The high temperature grown GaN layer provides a good foundation for subsequent growth of gallium nitride based semiconductors for nitride based semiconductor light emitting devices capable of generating long wavelength light.

  In the method according to the present invention, the first temperature may be not less than 550 degrees Celsius and not more than 850 degrees Celsius, and the second temperature may be not less than 950 degrees Celsius and not more than 1150 degrees Celsius.

In the method according to the present invention, the thickness of the Al _X2 Ga _1-X2 N layer is preferably 3 nm or more. According to the Al _X2 Ga _1-X2 N layer having this thickness, decomposition of In _X1 Ga _1-X1 N can be avoided.

  In the method according to the present invention, the thickness of the GaN is preferably 100 nm or more. According to the GaN layer having this thickness, an underlayer having good crystal quality can be provided.

In the method according to the present invention, after the substrate was placed in the growth furnace, the Al X2 _{Ga 1-X2} prior to the growth of the _N layer, the first while flowing a gas containing at least nitrogen as a constituent element in the growth furnace A step of raising the temperature of the substrate to a temperature of The hydrogen fraction of the gas is preferably from 0% to 5%. According to this method, if the hydrogen fraction is 5% or less, the promotion of decomposition of In _X1 Ga _{1 -X1} N in the hydrogen atmosphere is suppressed.

In the method according to the present invention, the substrate includes a support base and a nitride layer composed of the In _X1 Ga _1-X1 N (0 <X1 ≦ 1), and the nitride layer is 20 micrometers or more. It is preferable. This substrate is suitable for the growth of a nitride semiconductor layer containing indium for a nitride-based semiconductor light-emitting device capable of generating light having a long wavelength. In the method according to the present invention, the support substrate can be made of any material of GaN, sapphire, SiC, ZnO and GaAs. An epitaxial wafer for a nitride-based semiconductor light-emitting element can be provided using the In _X1 Ga _1-X1 N template.

In the method according to the present invention, the substrate may be an In _X1 Ga _1-X1 N substrate. The In _X1 Ga _1-X1 N surface is provided by an In _X1 Ga _1-X1 N substrate. An epitaxial wafer for a nitride-based semiconductor light-emitting device can be manufactured using a bulk In _X1 Ga _1-X1 N substrate.

In the method according to the present invention, the Al _X2 Ga _1-X2 N layer is preferably made of AlGaN. Since the Al—N bond is strong, the decomposition inhibiting action of In _X1 Ga _1-X1 N is provided.

The method according to the present invention may further include a step of growing an active layer on the GaN layer. Since this active layer is included in the gallium nitride based semiconductor stack formed on the In _X1 Ga _1-X1 N surface, it is suitable for a long wavelength nitride based semiconductor light emitting device.

  The method according to the present invention may further include a step of growing an InGaN layer after the growth of the GaN layer and before the growth of the active layer. The InGaN layer is thicker than the GaN layer. With this InGaN layer, an active layer suitable for a long wavelength nitride-based semiconductor light-emitting device can be grown.

In the method according to the present invention, prior to growing the Al _X2 Ga _1-X2 N layer, a nitride thick film made of In _X1 Ga _1-X1 N is deposited on a support by HVPE, A step of manufacturing a substrate can be further provided. The growth of the Al _X2 Ga _1-X2 N layer is performed by the HVPE method, and the growth of the GaN layer is performed by the MOVPE method. According to this method, while growing a nitride thick film consisting of _{In X1 Ga 1-X1} N by HVPE, growing the _{Al X2 Ga 1-X2} N layer thereon, the nitride-based semiconductor of the long wavelength A substrate for a light emitting element is formed. For this reason, it is not necessary to grow an Al _X2 Ga _{1 -X2} N layer before growing a gallium nitride based semiconductor for a nitride based semiconductor light emitting device.

Another aspect of the present invention is an epitaxial wafer for a nitride-based semiconductor light-emitting device. The epitaxial wafer includes (a) a substrate made of In _X1 Ga _1-X1 N (0 <X1 ≦ 1), and (b) Al _X2 Ga _1-X2 N (0 ≦ X2 ≦ 1) covering the surface of the substrate. A layer. Alternatively, the epitaxial wafer includes (a) a supporting substrate, (b) an In _X1 Ga _1-X1 N (0 <X1 ≦ 1) layer provided on the supporting substrate, and (c) the In _X1 Ga _{1 -X1} cover the surface of the N layer _{Al X2 Ga 1-X2 N (} 0 ≦ X2 ≦ 1) and a layer. The support base is made of any material of GaN, sapphire, SiC, ZnO and GaAs. According to this epitaxial wafer, no droplets or the like are generated when a nitride semiconductor light emitting device having a long wavelength is manufactured.

In the epitaxial wafer according to the present invention, the thickness of the Al _X2 Ga _1-X2 N is preferably 3 nm or more. According to the Al _X2 Ga _1-X2 N layer having this thickness, decomposition of In _X1 Ga _1-X1 N can be avoided.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, there is provided a method for producing an epitaxial wafer for a nitride-based semiconductor light-emitting device capable of generating light having a long wavelength while avoiding generation of droplets due to InGaN (InN). Provided. This epitaxial wafer is also provided.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, a method for producing an epitaxial wafer of the present invention and an embodiment related to the epitaxial wafer will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

FIG. 1 is a drawing showing a process flow of a method for producing an epitaxial wafer according to the present embodiment. FIG. 2 is a drawing showing the main steps of the method for producing the epitaxial wafer according to the present embodiment. Referring to the process flow 100, in step S101, a substrate 11 having a surface made of In _X1 Ga _1-X1 N (0 <X1 ≦ 1) is prepared. As the substrate 11, for example, an In _X1 Ga _1-X1 N template, an In _X1 Ga _1-X1 N bulk substrate, or the like can be used. An epitaxial wafer for a nitride-based semiconductor light-emitting device can be manufactured using a bulk In _X1 Ga _{1 -X1} N substrate, an In _X1 Ga _{1 -X1} N template, and the like. Preferably, In _X1 Ga _1-X1 N is a hexagonal crystal, and the normal line of the main surface of the substrate 11 is substantially perpendicular to the C axis or inclined at a slight off angle with respect to the C axis. is doing.

FIG. 3 is a diagram illustrating a configuration example of an In _X1 Ga _1-X1 N template. Referring to FIG. 3A, a substrate 11a is shown as an example of an In _X1 Ga _1-X1 N template. The substrate 11 a includes a support base 13 and a nitride layer 15 having an outermost surface made of In _X1 Ga _{1 -X1} N. The support base 13 can be made of any material such as GaN, sapphire, SiC, ZnO, and GaAs. A so-called low-temperature GaN layer 17a is preferably grown on the support base 13, and the nitride layer 15 is made of In _X1 Ga _1-X1 N. The growth temperature of the low-temperature GaN layer 17a is, for example, 500 degrees Celsius, and the film thickness is, for example, 25 nm.

Referring to FIG. 3B, a substrate 11b is shown as an example of an In _X1 Ga _1-X1 N template. Similarly to the substrate 11a, the substrate 11b includes a support base 13 and a nitride layer 15 having an outermost surface made of In _X1 Ga _1-X1 N. It is preferable to grow a so-called low-temperature GaN layer 17a and high-temperature GaN layer 17b on the support base 13. The growth temperature of the high-temperature GaN layer 17b is, for example, 1150 degrees Celsius and the film thickness is, for example, 500 nm.

In the templates 11a and 11b shown in FIGS. 3A and 3B, the nitride layer 15 is preferably 20 micrometers or more. The substrates 11a and 11b are suitable for growing a nitride semiconductor layer containing indium for a nitride-based semiconductor light-emitting element capable of generating light having a long wavelength. When the thickness is 20 micrometers or more, the strain of In _X1 Ga _{1 -X1} N can be reduced, which is suitable for growing an InGaN film having a large indium composition on the layer 15.

As shown in FIG. 2A, the substrate 11 is placed in the growth furnace 21. As the growth furnace 21, for example, a metal organic vapor phase growth furnace can be used. Thereafter, the temperature of the growth furnace 21 is changed from the room temperature to the growth temperature T1 while flowing the process gas G0. The process gas G0 can contain at least one of nitrogen and ammonia. In the temperature rising period prior to the growth of the Al _X2 Ga _1-X2 N layer, hydrogen may be contained in the process gas G0, but the hydrogen fraction is preferably 5% or less. If the hydrogen fraction is 5% or less, the decomposition promotion of In _X1 Ga _1-X1 N in the hydrogen atmosphere is suppressed. It is preferred that the hydrogen fraction is zero. There is no possibility of In _X1 Ga _{1 -X1} N decomposition due to hydrogen in the atmosphere.

In step S102, as shown in FIG. 2 (b), grown _{Al X2 Ga 1-X2 N (} 0 ≦ X2 ≦ 1) layer 19 at a first temperature T1 on the substrate 11. The Al _X2 Ga _1-X2 N layer 19 can be, for example, an n-conducting Al _0.02 Ga _0.98 N layer having a thickness of 10 nm. As the source gas G1, for example, TMGa, TMAl, and NH ₃ can be used. The growth temperature T1 is, for example, 800 degrees Celsius. The first temperature T1 is preferably not less than 550 degrees Celsius, for example. This is because the crystal quality can be improved at a temperature higher than this temperature. Moreover, it is preferable that 1st temperature T1 is 850 degrees C or less, for example. This is because if the temperature is lower than this temperature, decomposition of the surface of In _X1 Ga _{1 -X1} N during Al _X2 Ga _{1 -X2} N layer growth can be suppressed. When Al _X2 Ga _1-X2 N layer is formed of AlGaN, because strong Al-N bonds are _formed, the ones decomposition inhibitory action of the In _{X1 Ga 1-X1} N and excellent. _{Alternatively,} when the Al _{X2 Ga 1-X2} N layer is made of GaN, it becomes what crystal quality is good by only easier to migrate from Al group III element at low temperatures Ga. This GaN layer provides an action of suppressing decomposition of In _X1 Ga _1-X1 N.

The Al _X2 Ga _1-X2 N layer 19 covers the surface 10 of the substrate 11. The thickness D1 of the Al _X2 Ga _1-X2 N layer 19 is preferably 3 nm or more. According to the Al _X2 Ga _1-X2 N layer having this thickness, decomposition of In _X1 Ga _1-X1 N can be avoided. The thickness D1 is preferably 50 nm or less. Exceeding this thickness may cause a deterioration in the crystal quality of the Al _X2 Ga _1-X2 N layer.

In step S103, as shown in FIG. 2C, the GaN layer 23 is grown on the Al _X2 Ga _1-X2 N layer 19 at the second temperature T2. The GaN layer 23 has n conductivity, for example. As the source gas G2, for example, TMGa and NH ₃ can be included. The second temperature T2 is higher than the first temperature T1. Specifically, the growth temperature T2 is, for example, 1000 degrees Celsius. The second temperature T2 is preferably not less than 950 degrees Celsius, for example. This is because the crystal quality can be improved at a temperature higher than this temperature. The second temperature T2 is preferably 1150 degrees Celsius or less, for example. This is because, if the temperature is higher than this temperature, decomposition may proceed inside the crystal of In _X1 Ga _1-X1 N.

According to this step, before the GaN layer 23 having a good crystal quality is grown at a high temperature, the Al _X2 Ga _1-X2 N layer 19 is grown at a low temperature to cover the surface of In _X1 Ga _1-X1 N. Therefore, even in a high temperature atmosphere related to the growth of the GaN layer 23, decomposition of In _X1 Ga _{1 -X1} N can be avoided, and no droplets are generated. The high temperature grown GaN layer 23 provides a good foundation for subsequent growth of gallium nitride based semiconductors for nitride based semiconductor light emitting devices capable of generating long wavelength light.

After this step, the growth is completed and the substrate 11 is taken out from the growth furnace 21. An epitaxial wafer E0 for a long wavelength light emitting device is provided. Epitaxial wafer E0 has the following structure. The epitaxial wafer E0 having one structure includes an In _X1 Ga _1-X1 N substrate and an Al _X2 Ga _1-X2 N layer covering the surface of the substrate. The epitaxial wafer E0 having a different structure includes a support base made of a different material from the gallium nitride-based material, an In _X1 Ga _1-X1 N layer provided on the support base, and the surface of the In _X1 Ga _1-X1 N layer. And an Al _X2 Ga _1-X2 N layer covering the substrate. According to this epitaxial wafer E0, no droplets or the like are generated during the production of a long-wavelength nitride-based semiconductor light emitting device.

  In the invention according to the present embodiment, the following steps can be continued without being limited to the production of the epitaxial wafer E0. Next, as shown in FIG. 2 (d), a cladding layer, an active layer, an electron blocking layer, and a contact layer are sequentially deposited on the underlayer in a growth furnace 21.

In step S <b> 104, an In _X3 Ga _1-X3 N layer 25 for the cladding layer is grown on the GaN layer 23. The In _X3 Ga _1-X3 N layer 25 has n conductivity, for example. As the source gas, for example, TMGa, TMIn, and NH ₃ can be used. The growth temperature T3 of the In _X3 Ga _1-X3 N layer 25 is, for example, 800 degrees Celsius. The third temperature T3 is preferably not less than 650 degrees Celsius, for example. This is because the crystal quality can be improved at a temperature higher than this temperature. The third temperature T3 is preferably 900 degrees Celsius or less, for example. Below this temperature, the desired In composition can be obtained.

In step S105, as shown in FIG. 2D, the active layer 27 is grown on the In _X3 Ga _1-X3 N layer 25. The active layer 27 is formed to emit light having a long wavelength in a wavelength range of 480 nm to 600 nm. In the preferred embodiment, the active layer 27 can have a quantum well structure 29 and can have alternating barrier layers 31 and well layers 33. The well layer 33 can be made of, for example, InGaN or InAlGaN. The barrier layer 31 can be made of, for example, InGaN, InAlGaN, or GaN. The growth temperature _{T W} of the well layer 33 is preferably lower than the growth temperature _{T B} of the barrier layer 31. In step S106, the barrier layer 31 is grown. The growth temperature _{T B} is, for example, 800 degrees centigrade. In step S107, the well layer 33 is grown. The growth temperature _TW is, for example, 720 degrees Celsius. In order to obtain long-wavelength emission in the wavelength range of 480 nm to 600 nm, the well / barrier layer combination is preferably InGaN / InGaN, InGaN / InAlGaN, InGaN / GaN, or the like. In order to form a multiple quantum well structure, the growth of the barrier layer 31 and the well layer 33 can be repeated in step S108.

In step S109, a gallium nitride based semiconductor layer 35 containing indium is formed on the active layer 27. The gallium nitride based semiconductor layer 35 is provided for an electron block layer or a clad layer, for example. The conductivity of the gallium nitride based semiconductor layer 35 is preferably p-type. In the subsequent description of this embodiment, the gallium nitride based semiconductor layer 35 is formed for the electron block layer. The band gap of the gallium nitride based semiconductor layer 35 is larger than the band gap of the barrier layer 31. The thickness of the gallium nitride based semiconductor layer 35 is larger than the thickness of the barrier layer 31 and does not cause electron tunneling. The thickness of this layer 35 is, for example, 20 nm. The growth temperature T _EB is, for example, 800 degrees Celsius. As a material of the gallium nitride based semiconductor layer 35, for example, InAlGaN, InGaN, or the like can be used.

In step S <b> 110, a gallium nitride semiconductor layer 37 containing indium is formed on the gallium nitride semiconductor layer 35. The gallium nitride based semiconductor layer 37 is provided for a contact layer, for example. The conductivity of the gallium nitride based semiconductor layer 37 is p-type. The band gap of the gallium nitride based semiconductor layer 37 is smaller than the band gap of the gallium nitride based semiconductor layer 35. The amount of the p-type dopant added to the p-type gallium nitride based semiconductor layer 37 is relatively large so as to provide a good ohmic contact with the metal electrode. The thickness of this layer 37 is, for example, 50 nm. The growth temperature T _CON is, for example, 800 degrees Celsius. As the material of the gallium nitride based semiconductor layer 37, for example, InGaN, InAlGaN, or the like can be used.

  Using the above manufacturing method, as shown in FIG. 4A, an epitaxial wafer E1 for a light emitting diode (LED) structure was manufactured. An anode electrode and a cathode electrode were produced on the epitaxial wafer E1 to produce a light emitting diode element. When a current was applied, light emission at 530 nm was exhibited.

An example of the epitaxial wafer E1 is shown below.
In _X1 Ga _1-X1 N surface 11:
Al _X2 Ga _1-X2 N layer 19: Si-doped Al _0.02 Ga _0.98 N, 10 nm
GaN layer 23: Si-doped GaN, 150 nm
In _X3 Ga _1-X3 N layer 25: Si-doped In _0.1 Ga _0.9 N, 4 μm
Active layer 27
Well layer 33: undoped In _0.3 Ga _0.7 N, 3 nm
Barrier layer 31: undoped In _0.1 Ga _0.9 N, 15 nm
Gallium nitride semiconductor layer 35: Mg-doped In _0.02 Al _0.02 Ga _0.96 N, 20 nm
Gallium nitride based semiconductor layer 37: Mg-doped In _0.1 Ga _0.98 N, 50 nm.

For comparison, as shown in FIG. 4 (b), to produce an epitaxial wafer E _R for emitting diode (LED) structure. Epitaxial wafer _{E R} is directly grown the _{In X3 Ga 1-X3} N layer 45 on the substrate 11. In the epitaxial wafer _{E R,} on In _{X3 Ga 1-X3} N layer 45 in a similar deposition conditions and preparation of the epitaxial wafer E1, active layer 47, the electron blocking layer 55 and the contact layer 57, was produced. The active layer 47 includes a barrier layer 51 and a well layer 53.
An example of the epitaxial wafer E _R shown below.
In _X1 Ga _1-X1 N surface 11:
In _X3 Ga _1-X3 N layer 45: Si-doped In _0.1 Ga _0.9 N, 4 μm
Active layer 47
Well layer 53: undoped In _0.3 Ga _0.7 N, 3 nm
Barrier layer 51: undoped In _0.1 Ga _0.9 N, 15 nm
Gallium nitride based semiconductor layer 55: Mg-doped In _0.02 Al _0.02 Ga _0.96 N, 20 nm
Gallium nitride based semiconductor layer 57: Mg-doped In _0.1 Ga _0.98 N, 50 nm.

Compared to the surface of the epitaxial wafer E _R, the surface flatness of the epitaxial wafer E1 was excellent. It is considered that the excellent flatness of the epitaxial wafer E1 is provided by growing the InGaN layer and the InAlGaN layer on the high-temperature grown GaN layer 23. The surface of the epitaxial wafer E _R had rough for three-dimensional growth. InGaN grown at a low temperature is unlikely to cause migration, and therefore, it is considered that three-dimensional growth of InGaN is likely to occur. When InGaN is grown directly on the substrate 11, crystal growth is hindered by the influence of slight contamination on the surface of the substrate, and as a result, three-dimensional growth is considered to occur. On the other hand, the GaN layer 23 can be grown at a high temperature by the underlying Al _X2 Ga _{1 -X2} N layer 19. The GaN layer 23 exhibits an excellent migration property, and can provide a flat crystal surface by embedding a growth inhibition portion.

FIG. 5 is a drawing showing a procedure for producing an InGaN template. FIG. 6 is a drawing showing the main steps of a method for producing an epitaxial wafer according to the present embodiment. The InGaN templates 11a and 11b shown in FIG. 3 are produced, for example, according to the flow shown in FIG. For crystal growth in the InGaN templates 11a and 11b, for example, metal organic chemical vapor deposition, HVPE, or the like can be used. As shown in FIG. 6A, a template support base 13 is prepared. As described above, sapphire or the like can be used as the support base 13. In step S121, as shown in FIG. 6B, the support base 13 is set in the growth furnace, the process gas G3 is supplied to the growth furnace, and the support base 13 is thermally cleaned. In step S122, as shown in FIG. 6C, the source gas G4 is supplied to the growth furnace to grow the low-temperature GaN buffer layer 17a on the entire surface of the support base 13. The thickness of the low-temperature GaN buffer layer 17a is, for example, not less than 10 nm and not more than 100 nm. The growth temperature _TL is, for example, not less than 400 degrees Celsius and not more than 600 degrees Celsius. If necessary, as shown in FIG. 6D, the source gas G5 is supplied to the growth furnace to grow the high temperature GaN buffer layer 17b on the entire surface of the low temperature GaN buffer layer 17a. The thickness of the high-temperature GaN buffer layer 17b is, for example, 200 nm or more. Moreover, the thickness of the high temperature GaN buffer layer 17b is, for example, 5 μm or less. The growth temperature _TH is, for example, not less than 950 degrees Celsius and not more than 1200 degrees Celsius.

After growing the buffer layer 17a (or buffer layer 17b), in step S124, the source gas G6 is supplied to the growth reactor to grow the In _X1 Ga _1-X1 N layer 15. The thickness of the In _X1 Ga _1-X1 N layer 15 is, for example, 20 μm or more and 100 μm or less. The growth temperature is, for example, not less than 650 degrees Celsius and not more than 900 degrees Celsius. Thereafter, in step S125, the InGaN templates 11a and 11b are taken out from the growth furnace.

Alternatively, the Al _X2 Ga _{1 -X2} N layer 19 can be grown on the In _X1 Ga _{1 -X1} N layer 15 by performing the step S126 after the step S124. Thereafter, in step S127, the InGaN template including the Al _X2 Ga _1-X2 N layer 19 is taken out from the growth reactor. By using this InGaN template, a step for preventing the occurrence of droplets is not required at the beginning of the growth of the epitaxial film for the light emitting device, and light is emitted directly on the Al _X2 Ga _1-X2 N layer. An epitaxial stack for the device can be formed.

FIG. 7 is a drawing showing main steps of a method for manufacturing an In _X1 Ga _1-X1 N bulk substrate according to an embodiment. Referring to the process flow 102, in step S131, a support base is prepared. As the support, for example, a GaAs substrate, a sapphire substrate, a GaN substrate, or the like can be used. The support may include an oxide film mask layer as necessary. In step S132, an In _X1 Ga _1-X1 N thick film is grown on the support by the HVPE method. This thick film is preferably 300 μm or more in order to obtain a self-supporting bulk substrate. After growing the In _X1 Ga _1-X1 N thick film, the supply of the indium raw material is stopped, and in Step S133, a GaN film is grown on the In _X1 Ga _1-X1 N thick film by the HVPE method. The thickness of the GaN film grown by the HVPE method is preferably 50 nm or more and 500 nm or less, for example. By these steps, a crystal product having a crystal body including an InGaN thick film and a GaN cap film and a support is produced. In step S134, after the GaN film is grown, the crystal product is taken out of the HVPE growth furnace. If necessary, in step S135, the support is removed from the crystal product to obtain an independent crystal. The crystal body is subjected to polishing, cleaning, and the like for manufacturing a semiconductor substrate, whereby an In _X1 Ga _1-X1 N bulk substrate is manufactured.

The surface of the In _X1 Ga _1-X1 N bulk substrate is covered with a GaN film. By using the In _X1 Ga _{1 -X1} N bulk substrate, it is not necessary to grow an Al _X2 Ga _{1 -X2} N layer before growing a gallium nitride based semiconductor for a nitride based semiconductor light emitting device. In order to directly grow one or a plurality of GaN layers on the surface of the In _X1 Ga _1-X1 N substrate obtained by this fabrication method by metal organic vapor phase epitaxy (MOVPE) in Step S136, the temperature is 1000 degrees Celsius. The temperature can be raised to a temperature close to 50 degrees. Thereafter, one or a plurality of GaN, InGaN, and AlInGaN layers were grown to produce an epitaxial wafer for a gallium nitride based semiconductor light emitting device. The surface flatness of this epitaxial wafer was good.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

  As described above, according to the embodiment of the present invention, there is provided an epitaxial wafer for a nitride-based semiconductor light-emitting element that can generate light having a long wavelength without bothering generation of droplets. Also provided is a method of making this epitaxial wafer.

A green light-emitting element can be manufactured using In (Ga) N having a high indium composition. As the substrate, an InGaN substrate or an InN substrate is produced. In a GaN bulk substrate, a GaN epitaxial film is grown after performing a cleaning process by raising the temperature to 1000 degrees Celsius or higher in an atmosphere containing H ₂ . However, according to the inventor's knowledge, the method for growing a nitride-based epitaxial film on an In (Ga) N bulk substrate or template requires a different approach from the growth using a GaN bulk substrate.

  The epitaxial film first grown on the In (Ga) N substrate is preferably a high-temperature grown GaN film. Although the lattice constant of In (Ga) N is different from the lattice constant of GaN, the crystal quality of this GaN film is good and the surface flatness is also good. However, due to the difference in growth temperature between In (Ga) N and GaN, In (Ga) N is decomposed during the growth of the GaN film, and metal droplets are generated on the surface.

According to the inventor's study, in order to avoid metal droplets, it is preferable to use N ₂ by lowering the H ₂ ratio from the temperature rising atmosphere for GaN growth.

  In addition, it is important not to expose the In (Ga) N surface to high temperatures exceeding the range of about 550 degrees Celsius to 850 degrees Celsius. For this reason, after covering the In (Ga) N surface with a protective layer made of a gallium nitride-based semiconductor not containing indium, the temperature is raised to a high temperature exceeding the above temperature range, for example, around 1000 degrees Celsius, and a high quality GaN is grown.

  Alternatively, it is preferable to perform epitaxial growth on a substrate whose In (Ga) N surface is capped with a gallium nitride-based semiconductor not containing indium.

  By preventing exposure to the substrate surface of the gallium nitride-based material containing indium, decomposition of In (Ga) Nx can be suppressed during temperature rise. Therefore, generation | occurrence | production of a metal droplet is suppressed.

FIG. 1 is a drawing showing a process flow of a method for producing an epitaxial wafer according to the present embodiment. FIG. 2 is a drawing showing the main steps of a method for producing an epitaxial wafer according to the present embodiment. FIG. 3 is a diagram illustrating a configuration example of an In _X1 Ga _1-X1 N template. Figure 4 is a drawing that shows the structure of an epitaxial wafer E1, _{E R} for LED structure. FIG. 5 is a drawing showing a procedure for producing an InGaN template. FIG. 6 is a drawing showing the main steps of a method for producing an epitaxial wafer according to the present embodiment. FIG. 7 is a drawing showing main steps of a method for manufacturing an In _X1 Ga _1-X1 N bulk substrate according to an embodiment.

Explanation of symbols

10 ... substrate surface, 11 ... _{substrate, 1a, 11b ... In X1 Ga} 1-X1 N template substrate 1, 13 ... support base 15 ... nitride layer, 17a ... low-temperature GaN layer, 17b ... high temperature GaN layer, 19 ... Al _{X2Ga1 -X2N} layer, 21 ... growth reactor, 23 ... GaN layer, 25 ... _{InX3Ga1 -X3N} layer, 27 ... active layer, 29 ... quantum well structure, 31 ... barrier layer, 33 ... well layer, 35 ... Gallium nitride semiconductor layer, 37 ... Gallium nitride semiconductor layer, E0, E1 ... Epitaxial wafer

Claims (15)

A method for producing an epitaxial wafer for a nitride-based semiconductor light-emitting device, comprising:
Growing an Al _X2 Ga _1-X2 N (0 ≦ X2 ≦ 1) layer at a first temperature on a substrate having a surface made of In _X1 Ga _1-X1 N (0 <X1 ≦ 1);
Growing a GaN layer on the Al _X2 Ga _1-X2 N layer at a second temperature,
The Al _X2 Ga _1-X2 N layer covers the surface of the substrate;
The method of claim 1, wherein the first temperature is lower than the second temperature. The first temperature is not less than 550 degrees Celsius and not more than 850 degrees Celsius,
The method of claim 1, wherein the second temperature is not less than 950 degrees Celsius and not more than 1150 degrees Celsius. The method according to claim _1, wherein the thickness of the Al _X2 Ga _1-X2 N is 3 nm or more.   The method according to claim 1, wherein the GaN has a thickness of 100 nm or more. After placing the substrate in the growth furnace, prior to the growth of the Al _X2 Ga _1-X2 N layer, the temperature of the substrate is brought to the first temperature while flowing a gas containing at least nitrogen as a constituent element to the growth furnace. Further comprising the step of raising
The method according to any one of claims 1 to 4, wherein the hydrogen fraction of the gas is not less than 0% and not more than 5%. The substrate includes a support base and a nitride layer provided on the support base and made of the In _X1 Ga _1-X1 N,
The method according to any one of claims 1 to 5, wherein the nitride layer is 20 micrometers or more.   The method according to claim 6, wherein the support base is made of any one of GaN, sapphire, SiC, ZnO, and GaAs. The method according to claim 1, wherein the substrate is an In _X1 Ga _1-X1 N substrate. The method according to claim _1, wherein the Al _X2 Ga _1-X2 N layer is made of AlGaN.   The method according to claim 1, further comprising growing an active layer on the GaN layer. Further comprising the step of growing an InGaN layer after the growth of the GaN layer and before the growth of the active layer,
The method of claim 10, wherein the thickness of the InGaN layer is greater than the thickness of the GaN layer. Prior to growing the Al _X2 Ga _1-X2 N layer, a step of depositing a nitride thick film made of In _X1 Ga _1-X1 N on a support by HVPE method to further produce the substrate Prepared,
The growth of the Al _X2 Ga _1-X2 N layer is performed by an HVPE method,
The method according to claim 1, wherein the growth of the GaN layer is performed by a MOVPE method. An epitaxial wafer for a nitride semiconductor light emitting device,
A substrate made of In _X1 Ga _1-X1 N (0 <X1 ≦ 1);
An epitaxial wafer comprising: an Al _X2 Ga _1-X2 N (0 ≦ X2 ≦ 1) layer covering the surface of the substrate. An epitaxial wafer for a nitride semiconductor light emitting device,
A support substrate;
An In _X1 Ga _1-X1 N (0 <X1 ≦ 1) layer provided on the support substrate;
An Al _X2 Ga _1-X2 N (0 ≦ X2 ≦ 1) layer covering the surface of the In _X1 Ga _1-X1 N layer,
The epitaxial wafer characterized in that the support substrate is made of any material of GaN, sapphire, SiC, ZnO and GaAs. 15. The epitaxial wafer according to claim 13, wherein a thickness of the Al _X2 Ga _1-X2 N is 3 nm or more.

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