CN119008406A - High-photoelectric-performance Al regulated and controlled by patterned sapphire substratexGa1-xN epitaxial layer preparation method - Google Patents
High-photoelectric-performance Al regulated and controlled by patterned sapphire substratexGa1-xN epitaxial layer preparation method Download PDFInfo
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- 229910052594 sapphire Inorganic materials 0.000 title claims abstract description 68
- 239000010980 sapphire Substances 0.000 title claims abstract description 68
- 238000002360 preparation method Methods 0.000 title claims abstract description 20
- 230000001105 regulatory effect Effects 0.000 title claims abstract description 18
- 239000000758 substrate Substances 0.000 claims abstract description 66
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 44
- 238000000034 method Methods 0.000 claims abstract description 34
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 20
- 230000008021 deposition Effects 0.000 claims description 6
- 238000000059 patterning Methods 0.000 claims description 6
- 230000000630 rising effect Effects 0.000 claims description 2
- 229910002704 AlGaN Inorganic materials 0.000 abstract description 12
- JLTRXTDYQLMHGR-UHFFFAOYSA-N trimethylaluminium Chemical compound C[Al](C)C JLTRXTDYQLMHGR-UHFFFAOYSA-N 0.000 abstract description 12
- XCZXGTMEAKBVPV-UHFFFAOYSA-N trimethylgallium Chemical compound C[Ga](C)C XCZXGTMEAKBVPV-UHFFFAOYSA-N 0.000 abstract description 8
- 238000005229 chemical vapour deposition Methods 0.000 abstract description 6
- 229910052751 metal Inorganic materials 0.000 abstract description 6
- 239000002184 metal Substances 0.000 abstract description 6
- 230000006911 nucleation Effects 0.000 abstract description 4
- 238000010899 nucleation Methods 0.000 abstract description 4
- 229910052782 aluminium Inorganic materials 0.000 abstract description 3
- 239000012159 carrier gas Substances 0.000 abstract description 2
- 229910052733 gallium Inorganic materials 0.000 abstract description 2
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 2
- 239000010410 layer Substances 0.000 description 154
- 229920002120 photoresistant polymer Polymers 0.000 description 12
- 230000008569 process Effects 0.000 description 10
- 239000000463 material Substances 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 8
- 238000010438 heat treatment Methods 0.000 description 8
- 239000000203 mixture Substances 0.000 description 8
- 239000013078 crystal Substances 0.000 description 6
- 238000000151 deposition Methods 0.000 description 5
- 238000005530 etching Methods 0.000 description 4
- 230000001965 increasing effect Effects 0.000 description 4
- 238000005424 photoluminescence Methods 0.000 description 4
- 239000012495 reaction gas Substances 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 230000001276 controlling effect Effects 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 238000005137 deposition process Methods 0.000 description 2
- 239000011229 interlayer Substances 0.000 description 2
- 238000000103 photoluminescence spectrum Methods 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000005669 field effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
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- 238000013508 migration Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000005693 optoelectronics Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000005622 photoelectricity Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910002058 ternary alloy Inorganic materials 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 230000005533 two-dimensional electron gas Effects 0.000 description 1
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- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/16—Controlling or regulating
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
- C30B29/403—AIII-nitrides
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- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
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- C30B29/406—Gallium nitride
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Abstract
本发明提供了一种利用图案化蓝宝石衬底调控的高光电性能AlxGa1‑xN外延层制备方法，该制备方法的步骤为：采用金属有机化学气相沉积系统在c面蓝宝石衬底上生长AlxGa1‑xN外延层，分别以三甲基镓(TMGa)、三甲基铝(TMAl)和氨气(NH3)作为Ga、Al和N的生长源，高纯H2作为载气。将蓝宝石衬底在H2环境中热清洗，然后沉积一层薄的低温GaN成核层。再生长高温GaN模板和AlxGa1‑xN外延层。在AlxGa1‑xN的生长过程中，改变TMAl的流速和反应器的压力，从而生长不同Al含量的AlGaN外延层。
The present invention provides a method for preparing an Al x Ga 1‑x N epitaxial layer with high photoelectric performance regulated by a patterned sapphire substrate. The preparation method comprises the following steps: growing an Al x Ga 1‑x N epitaxial layer on a c-plane sapphire substrate by a metal organic chemical vapor deposition system, using trimethyl gallium (TMGa), trimethyl aluminum (TMAl) and ammonia (NH 3 ) as growth sources of Ga, Al and N respectively, and using high-purity H 2 as a carrier gas. The sapphire substrate is thermally cleaned in an H 2 environment, and then a thin low-temperature GaN nucleation layer is deposited. A high-temperature GaN template and an Al x Ga 1‑x N epitaxial layer are then grown. During the growth of Al x Ga 1‑x N, the flow rate of TMAl and the pressure of a reactor are changed, so as to grow AlGaN epitaxial layers with different Al contents.
Description
Technical Field
The invention belongs to the technical field of semiconductor photoelectricity, and particularly relates to a preparation method of a high-photoelectricity Al xGa1-x N epitaxial layer regulated and controlled by a patterned sapphire substrate.
Background
AlGaN is used as a ternary alloy, the direct band gap of the AlGaN can be changed within the range of 3.42-6.20eV by adjusting the Al component, and the AlGaN material is widely applied to ultraviolet photodetectors, light-emitting diodes and laser diode devices. The high Al content deteriorates the crystal quality of the AlGaN epitaxial layer, and the biaxial tensile strain generated by AlGaN during the growth process results in low Al incorporation efficiency. This limits the research on the high Al content and the crystallization quality of AlGaN thin films. Growth of AlGaN with high Al composition on sapphire substrates is a great challenge due to the large lattice and thermal expansion mismatch between the sapphire substrate and the epitaxial layers, and the low surface mobility of Al. Therefore, high temperature growth of GaN or AlN layers as strain relaxed layers may be considered to enhance the structural properties of the nitride material. In addition, the crystalline quality of AlGaN/GaN heterojunction materials affects their electrical properties, which is closely related to the layer structure and growth process of the materials. Threading dislocations, known as leakage current paths, reduce electron mobility, thereby significantly degrading the performance of GaN-based devices.
Disclosure of Invention
Aiming at the technical problems, the invention provides a preparation method of a high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by a patterned sapphire substrate. The Al component content is adjusted by growing Al xGa1-x N heterojunction material on the patterned sapphire substrate to prepare an epitaxial layer with low threading dislocation density and internal stress, so that the optical and electrical properties of the device are improved.
The aim of the invention is realized by the following technical scheme:
A preparation method of a high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by a patterned sapphire substrate comprises the following steps:
1) Preparing a patterned sapphire substrate;
2) Epitaxially growing a low-temperature GaN buffer layer on the patterned sapphire substrate;
3) Epitaxially growing a high-temperature GaN primary epitaxial layer on the low-temperature GaN buffer layer;
4) And epitaxially growing an Al xGa1-x N epitaxial layer on the high-temperature GaN primary epitaxial layer.
Preferably, the patterned sapphire substrate in the step 1) is prepared by patterning c-plane sapphire, the patterning type is any one of conical, columnar, bowl-shaped, hole-shaped and step-shaped, the patterns are distributed periodically, the pattern interval is 1-5 μm, and the pattern depth is 0.2-10 μm.
Preferably, the column is a column or a polygon column, the bowl shape is a round pier or a prism pier, the hole shape is a round hole or a polygon hole, and the step shape is a prism table or a cone table.
Preferably, the growth temperature of the low-temperature GaN buffer layer in the step 2) is 500-900 ℃, the temperature rising rate is 0.1-2 ℃/s, the V/III ratio is 2500-4500, the ammonia flow is controlled to be 500-3000sccm, and the deposition thickness is 0.2-0.4 μm.
Preferably, the high temperature GaN primary epitaxial layer in step 3) is formed by alternately growing a first GaN layer and a second GaN layer, and the number of alternating periods is 1-100.
Preferably, the growth conditions of the first GaN layer are: the growth temperature is 1000-1050 ℃, the V/III ratio is 800-1800, the ammonia flow is 0.1-1000sccm, and the thickness is 50-200nm.
Preferably, the growth conditions of the second GaN layer are: the growth temperature is 1050-1200 ℃, the ammonia flow is 1000-50000sccm, the V/III ratio is 4000-6500, and the thickness is 5-50nm.
Preferably, the TMAL flow rate used for the Al xGa1-x N epitaxial layer growth in the step 4) is 9.8-60 mu mol/min, the growth temperature is 1000-1100 ℃, and the growth thickness is 50-500nm.
Preferably, the pressure of the Al xGa1-x N epitaxial layer growth reactor in the step 4) is 32.5-98.2torr.
The invention provides a method for reducing the threading dislocation density of an epitaxial layer by a multi-type patterning strategy of a substrate, and further obtaining a high-quality GaN interlayer by adjusting the growth temperature and flow control of the layer. In the initial stage of high-temperature GaN growth, the size of the 3D nucleation island can be increased and the density of the island can be reduced by increasing the transverse growth rate with a low V/III ratio, so that the combination between islands can be realized, and the growth mode is changed into a quasi-two-dimensional growth mode. In an Al xGa1-x N/GaN heterostructure field effect transistor, an increase in Al mole fraction means an increase in two-dimensional electron gas density and carrier concentration in the channel. For larger 2DEG densities, the Al mole fraction of the Al xGa1-x N layer can be simply increased, as most of the carriers are induced by the piezoelectric polarization of the strained Al xGa1-x N barrier. The quality improvement preparation of the high Al component Al xGa1-x N epitaxial layer is realized by changing the flow rate and the growth temperature of trimethylaluminum.
Drawings
FIG. 1 is a process flow diagram of an embodiment of a method for fabricating a high-photoelectric-performance Al xGa1-x N epitaxial layer using patterned sapphire substrate modulation in the examples;
FIG. 2 is a schematic structural diagram of a product obtained by a preparation method of a high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by a patterned sapphire substrate in an embodiment;
Fig. 3 is a schematic cross-sectional structure of the sapphire substrate of example 1 in a conical pattern;
FIG. 4 is an inverted spatial spectrum of Al xGa1-x N/GaN at 24% Al composition of example 1;
FIG. 5 is a photoluminescence spectrum of Al xGa1-x N/GaN under three Al components of examples 1-3;
FIG. 6 is an XRD diffraction pattern of the sample of example 1;
FIG. 7 is an XRD diffraction pattern of comparative example 1 GaN;
fig. 8 is an XRD diffractogram of AlGaN prepared with the planar substrate of comparative example 2.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited to the scope indicated by the examples. These examples are provided only for illustrating the present invention and are not intended to limit the scope of the present invention. Further, after reading the present disclosure, those skilled in the art may make various modifications to the present disclosure, and such equivalent variations are also within the scope of the present disclosure as defined in the appended claims.
The invention adopts a metal organic chemical vapor deposition system to grow an Al xGa1-x N epitaxial layer on a c-plane sapphire substrate, and uses trimethyl gallium (TMGa), trimethyl aluminum (TMAL) and ammonia (NH 3) as growth sources of Ga, al and N respectively, and high-purity H 2 is used as carrier gas. Referring to the process flow diagram of fig. 1, a product having a structure as shown in fig. 2 is produced.
Example 1
The preparation method of the high-photoelectric-performance Al 0.24Ga0.76 N epitaxial layer regulated and controlled by the patterned sapphire substrate in the embodiment comprises the following steps:
(1) Preparation of patterned sapphire: in the step, specifically, a thin layer of photoresist is spin-coated on the surface of a c-plane sapphire substrate, then patterns on a mask plate are copied to the photoresist through procedures of pre-baking, exposure and the like, and then the photoresist is used as a mask to be processed through processes of etching and the like, so that the cone-shaped sapphire patterned substrate is finally formed, the patterns are regularly and periodically arranged, the period interval is 5 mu m, and the depth of the patterns is 2 mu m. The cross-sectional structure of the cone-like pattern is shown in fig. 3.
(2) Epitaxially growing a low-temperature GaN buffer layer on the patterned sapphire substrate, heating to 515 ℃, preheating the patterned sapphire substrate for 10min, preferably using trimethylgallium with the purity of 5N as a target source, using ammonia gas as a reaction gas, adopting a metal organic chemical vapor deposition method to grow the GaN buffer layer, wherein the growth temperature is 625 ℃, the heating rate is 0.5 ℃/s, the V/III ratio is 3200, the ammonia gas flow is controlled to 1500sccm, and the low-temperature GaN buffer layer is obtained by growth, wherein the preferred thickness of the GaN buffer layer is 0.25 mu m.
(3) And epitaxially growing a high-temperature GaN primary epitaxial layer on the low-temperature GaN buffer layer. In this step, specifically, the high-temperature GaN primary epitaxial layer is formed by alternately growing the first GaN layer and the second GaN layer, the number of alternating periods is preferably 50, and the conditions for growing the first GaN layer and the second GaN layer are different; the growth conditions of the first GaN layer are as follows: the growth temperature is 1000 ℃, the V/III ratio is 1000, the ammonia flow is 500sccm, and the thickness is preferably 80nm; the growth conditions of the second GaN layer are as follows: the growth temperature is 1100 ℃, the ammonia flow is 10000sccm, the V/III ratio is 4500, the thickness is preferably 30nm, the partial pressure of N 2 is 7GPa, and the total thickness of the alternate layer deposition is preferably 5.5 μm.
(4) And epitaxially growing an Al 0.24Ga0.76 N epitaxial layer on the high-temperature GaN primary epitaxial layer, wherein the TMAL flow rate used for growing the Al 0.24Ga0.76 N epitaxial layer is 25 mu mol/min, the growth temperature is 1050 ℃, the heating rate is 0.5 ℃/s, the growth preferred thickness is 200nm, and the pressure of a reactor is controlled to be 75torr. The Al 0.24Ga0.76 N photoluminescence eigenpeak was at 318nm as shown in fig. 5. The XRD diffractogram of the sample is shown in figure 6.
Example 2
The preparation method of the high-photoelectric-performance Al 0.34Ga0.66 N epitaxial layer regulated and controlled by the patterned sapphire substrate comprises the following steps:
(1) Preparation of patterned sapphire. In the step, specifically, a thin layer of photoresist is spin-coated on the surface of a c-plane sapphire substrate, then patterns on a mask plate are copied to the photoresist through procedures of pre-baking, exposure and the like, and then the photoresist is used as a mask for processing through processes such as etching and the like, so that the sapphire patterned substrate is finally formed. A patterned sapphire substrate is prepared, wherein the type of the patterned sapphire substrate is columnar, in particular cylindrical, patterns are regularly and periodically arranged, the period interval is 1 mu m, and the depth of the patterns is 0.2 mu m.
(2) A low temperature GaN buffer layer is epitaxially grown on the patterned sapphire substrate. In this step, specifically, the temperature is raised to 500 ℃, the patterned sapphire substrate is preheated for 8min, preferably trimethylgallium with a purity of 5N is used as a target source, ammonia gas is used as a reaction gas, the growth of the GaN buffer layer is performed by adopting a metal organic chemical vapor deposition method, the growth temperature is 500 ℃, the temperature raising rate is 0.1 ℃/s, the V/III ratio is 2500, the ammonia gas flow is controlled to 500sccm, and the low-temperature GaN buffer layer is obtained by growth, wherein the preferable thickness of the GaN buffer layer is 0.2 μm.
(3) And epitaxially growing a high-temperature GaN primary epitaxial layer on the low-temperature GaN buffer layer. In this step, specifically, the high-temperature GaN primary epitaxial layer is formed by alternately growing the first GaN layer and the second GaN layer, the number of alternating periods is preferably 4, and the conditions for growing the first GaN layer and the second GaN layer are different; the growth conditions of the first GaN layer are as follows: the growth temperature is 1000 ℃, the V/III ratio is 800, the ammonia flow is 0.1sccm, and the thickness is preferably 200nm; the growth conditions of the second GaN layer are as follows: the growth temperature is 1050 ℃, the ammonia flow is 1000sccm, the V/III ratio is 4000, and the thickness is preferably 50nm. It can be seen that the growth temperature of the first GaN layer is lower than that of the second GaN layer, and the V/III ratio of the first GaN layer is lower than that of the second GaN layer, i.e., the first GaN layer is a low temperature low V/III ratio GaN layer, and the second GaN layer is a high temperature high V/III ratio GaN layer. Wherein the partial pressure of N 2 is 6GPa and the total thickness of the alternate layer deposition is preferably 1 μm after the preferred period of growth.
(4) And epitaxially growing an Al 0.34Ga0.66 N epitaxial layer on the high-temperature GaN primary epitaxial layer. In this step, TMAL flow rate used for growth of the Al 0.34Ga0.66 N epitaxial layer is 40. Mu. Mol/min, growth temperature is 1000 ℃, heating rate is 0.5 ℃/s, and growth thickness is preferably 50nm. The reactor pressure was controlled at 32.5torr. As shown in FIG. 5, the photoluminescence eigenpeak of Al 0.34Ga0.66 N is located at 299nm.
Example 3
The preparation method of the high-photoelectric-performance Al 0.47Ga0.53 N epitaxial layer regulated and controlled by the patterned sapphire substrate comprises the following steps:
(1) Preparation of patterned sapphire. In the step, specifically, a thin layer of photoresist is spin-coated on the surface of a c-plane sapphire substrate, then patterns on a mask plate are copied to the photoresist through procedures of pre-baking, exposure and the like, and then the photoresist is used as a mask for processing through processes such as etching and the like, so that the sapphire patterned substrate is finally formed. The patterned sapphire substrate is prepared, the type of the patterned sapphire substrate is bowl-shaped, in particular round piers, the patterns are regularly and periodically arranged, the period interval is 4 mu m, and the depth of the patterns is 3 mu m.
(2) A low temperature GaN buffer layer is epitaxially grown on the patterned sapphire substrate. In this step, specifically, the temperature is raised to 510 ℃, the patterned sapphire substrate is preheated for 9min, preferably trimethylgallium with a purity of 5N is used as a target source, ammonia is used as a reaction gas, the growth of the GaN buffer layer is performed by adopting a metal organic chemical vapor deposition method, the growth temperature is 700 ℃, the temperature raising rate is 1 ℃/s, the V/III ratio is 4000, the ammonia flow is controlled to 1000sccm, and the low-temperature GaN buffer layer is obtained by growth, wherein the preferred thickness of the GaN buffer layer is 0.3 μm.
(3) And epitaxially growing a high-temperature GaN primary epitaxial layer on the low-temperature GaN buffer layer. In this step, specifically, the high-temperature GaN primary epitaxial layer is formed by alternately growing the first GaN layer and the second GaN layer, the number of alternating periods is preferably 50, and the conditions for growing the first GaN layer and the second GaN layer are different; the growth conditions of the first GaN layer are as follows: the growth temperature is 1010 ℃, the V/III ratio is 1500, the ammonia flow is 500sccm, and the thickness is preferably 50nm; the growth conditions of the second GaN layer are as follows: the growth temperature is 1100 ℃, the ammonia flow is 40000sccm, the V/III ratio is 6000, and the thickness is preferably 30nm. It can be seen that the growth temperature of the first GaN layer is lower than that of the second GaN layer, and the V/III ratio of the first GaN layer is lower than that of the second GaN layer, i.e., the first GaN layer is a low temperature low V/III ratio GaN layer, and the second GaN layer is a high temperature high V/III ratio GaN layer. Wherein the partial pressure of N 2 is 7GPa and the total thickness of the alternate layer deposition is preferably 4 μm after the preferred period of growth.
(4) And (5) epitaxially growing on the high-temperature GaN primary epitaxial layer to obtain the Al 0.47Ga0.53 N epitaxial layer. In this step, TMAL flow rate used for growth of Al 0.47Ga0.53 N epitaxial layer is 60 μmol/min, growth temperature is 1010 ℃, heating rate is 3 ℃/s, and growth thickness is preferably 100nm. The reactor pressure was controlled at 50.5torr. As shown in FIG. 5, the Al 0.47Ga0.53 N photoluminescence eigenpeak was located at 318nm.
Example 4
The preparation method of the high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by the patterned sapphire substrate comprises the following steps:
(1) Preparation of patterned sapphire. In the step, specifically, a thin layer of photoresist is spin-coated on the surface of a c-plane sapphire substrate, then patterns on a mask plate are copied to the photoresist through procedures of pre-baking, exposure and the like, and then the photoresist is used as a mask for processing through processes such as etching and the like, so that the sapphire patterned substrate is finally formed. A patterned sapphire substrate was prepared, which was of the type of holes, specifically circular holes, in a regular periodic arrangement with a period spacing of 5 μm and a pattern depth of 10 μm.
(2) A low temperature GaN buffer layer is epitaxially grown on the patterned sapphire substrate. In this step, specifically, the temperature is raised to 520 ℃, the patterned sapphire substrate is preheated for 10min, preferably trimethylgallium with a purity of 5N is used as a target source, ammonia is used as a reaction gas, the growth of the GaN buffer layer is performed by adopting a metal organic chemical vapor deposition method, the growth temperature is 900 ℃, the temperature raising rate is 2 ℃/s, the V/III ratio is 4500, the ammonia flow is controlled to 3000sccm, and the low-temperature GaN buffer layer is obtained by growth, wherein the preferable thickness of the GaN buffer layer is 0.4 μm.
(3) And epitaxially growing a high-temperature GaN primary epitaxial layer on the low-temperature GaN buffer layer. In this step, specifically, the high-temperature GaN primary epitaxial layer is formed by alternately growing the first GaN layer and the second GaN layer, the number of alternating periods is preferably 100, and the conditions for growing the first GaN layer and the second GaN layer are different; the growth conditions of the first GaN layer are as follows: the growth temperature is 1050 ℃, the V/III ratio is 1800, the ammonia flow is 1000sccm, and the thickness is preferably 70nm; the growth conditions of the second GaN layer are as follows: the growth temperature is 1200 ℃, the ammonia flow is 50000sccm, the V/III ratio is 6500, and the thickness is preferably 5nm. It can be seen that the growth temperature of the first GaN layer is lower than that of the second GaN layer, and the V/III ratio of the first GaN layer is lower than that of the second GaN layer, i.e., the first GaN layer is a low temperature low V/III ratio GaN layer, and the second GaN layer is a high temperature high V/III ratio GaN layer. Wherein the partial pressure of N 2 is 8GPa and the total thickness of the alternate layer deposition after the growth preference period is preferably 7.5 μm.
(4) And (5) epitaxially growing on the high-temperature GaN primary epitaxial layer to obtain the Al xGa1-x N epitaxial layer. In this step, TMAL flow rate used for growth of Al xGa1-x N epitaxial layer is 60 μmol/min, growth temperature is 1100 ℃, heating rate is 5 ℃/s, and growth thickness is 500nm. The reactor pressure was controlled at 98.2torr.
Example 5
Referring to the method of example 1, except that the patterned sapphire substrate prepared in step (1) was of a stepped, specifically prismatic, type.
Example 6
Referring to the method of example 1, the difference is that the growth of the Al xGa1-x N epitaxial layer prepared in step (4) uses TMAL flow rate of 9.8. Mu. Mol/min.
Comparative example 1
This comparative example differs from the preparation procedure of example 1 in that the Al xGa1-x N layer was omitted, i.e., the low temperature GaN buffer layer and the high temperature GaN primary epitaxial layer were deposited directly on the substrate in sequence, and the deposition process conditions were the same as in example 1. The XRD diffraction pattern of GaN is shown in FIG. 7.
Comparative example 2
This comparative example differs from the preparation procedure of example 1 in that planar sapphire (i.e., not patterned) was used as a substrate, and a low temperature GaN buffer layer, a high temperature GaN primary epitaxial layer, and a high Al composition Al xGa1-x N epitaxial layer were sequentially deposited, with the same deposition process conditions as in example 1. The XRD diffraction pattern of AlGaN prepared with a planar substrate is shown in fig. 8. The peak half width of AlGaN in the XRD pattern of example 1 is significantly smaller than that of comparative example 2, indicating that the sample crystal quality of example 1 is better than that of comparative example.
Fig. 3 is a schematic cross-sectional structure of the sapphire substrate in the embodiment 1 with a conical pattern, and it can be seen that under the condition of a large period interval distance, the substrate interface will not have non-merged voids, so as to avoid the problem of stress non-uniformity caused by the existence of voids.
FIG. 4 is an inverted spatial spectrum of Al xGa1-x N/GaN at 24% Al composition (corresponding to example 1). It can be seen that there is a partial strain between the GaN and Al xGa1-x N epitaxial layers, the in-plane strain of the epitaxial layers increases with increasing Al composition, and when the Al composition is 14%, the Al xGa1-x N/GaN heterostructure exhibits pseudomorphic growth, with in-plane strain of zero.
FIG. 5 is a photoluminescence spectrum of Al xGa1-x N/GaN under three Al components of examples 1-3. The intrinsic photoluminescence intensity of the Al xGa1-x N epitaxial layer becomes stronger with the increase of the Al composition, and the crystal quality is lowered because the surface migration of Al atoms is much lower than that of Ga atoms, and nucleation growth is suppressed with the increase of the Al composition, resulting in a decrease in the crystal crystallization quality. In Al xGa1-x N/GaN materials, threading dislocations act as impurities and non-radiative centers for deep levels, and the intensity of their near-band edge emission peaks is largely dependent on dislocations in the epitaxial layer.
The mechanism and advantages of the performance of the high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by the patterned sapphire substrate are described: first, by performing patterning treatment on a sapphire substrate, various periodically arranged microstructures such as cones, columns, bowls, and the like can be formed. These microstructures not only provide a more uniform nucleation environment, reduce dislocation density, but also improve the quality of GaN crystals at high temperatures, thereby enhancing their high temperature stability and chemical stability. The introduction of the low-temperature GaN buffer layer is important for the subsequent growth of a high-quality Al xGa1-x N epitaxial layer. And secondly, the interface formed between the low-temperature GaN buffer layer and the high-temperature GaN primary epitaxial layer on the sapphire substrate is patterned, so that better interlayer combination and reduction of stress concentration points are realized. Through alternately growing the GaN layers under different conditions (low temperature low V/III ratio and high temperature high V/III ratio), the thickness and quality of the GaN layers can be effectively controlled, and the uniformity and crystal quality of the final Al xGa1-x N epitaxial layer are further affected. Furthermore, by precisely controlling the flow rate of TMAl and the pressure of the reactor, alGaN epitaxial layers with different Al contents can be adjusted in the growth process of Al xGa1-x N. The method can not only improve the problem of the doping rate of the Al component, but also optimize the electrical performance of the device by adjusting the layer structure and the growth process. Finally, the present invention also emphasizes the control of the rate of temperature rise in particular. The preferred heating rate is 0.1-2.3 deg.c/s, since too fast a heating rate may initiate cracking of the high temperature GaN epitaxial layer. This helps to avoid cracking and other defects during growth, further improving the quality and reliability of the material.
In summary, the preparation method of the high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by the patterned sapphire substrate realizes the epitaxial layer growth with low dislocation density and excellent uniformity by finely controlling the growth conditions and parameter settings of the material. This not only improves the optoelectronic properties of the material, but also provides a powerful technical support for improving the overall performance of the semiconductor device.
Claims (9)
1. The preparation method of the high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by the patterned sapphire substrate is characterized by comprising the following steps of:
1) Preparing a patterned sapphire substrate;
2) Epitaxially growing a low-temperature GaN buffer layer on the patterned sapphire substrate;
3) Epitaxially growing a high-temperature GaN primary epitaxial layer on the low-temperature GaN buffer layer;
4) And epitaxially growing an Al xGa1-x N epitaxial layer on the high-temperature GaN primary epitaxial layer.
2. The method for preparing the Al xGa1-x N epitaxial layer with high photoelectric performance by using the patterned sapphire substrate as claimed in claim 1, wherein the patterned sapphire substrate in step 1) is prepared by patterning c-plane sapphire, the patterning type is any one of conical, columnar, bowl-shaped, hole-shaped and step-shaped, the patterns are distributed periodically, the pattern interval is 1-5 μm, and the pattern depth is 0.2-10 μm.
3. The method for preparing the high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by using the patterned sapphire substrate according to claim 2, wherein the columnar shape is a cylinder or a polygon prism, the bowl shape is a round pier or a prism pier, the hole shape is a round hole or a polygon hole, and the step shape is a prism table or a frustum.
4. The method for preparing a high photoelectric performance Al xGa1-x N epitaxial layer by using patterned sapphire substrate according to claim 1, wherein the growth temperature of the low-temperature GaN buffer layer in step 2) is 500-900 ℃, the temperature rising rate is 0.1-2.0 ℃/s, the V/III ratio is 2500-4500, the ammonia flow is controlled to be 500-3000sccm, and the deposition thickness is 0.2-0.4 μm.
5. The method for preparing the high-photoelectric-performance Al xGa1-x N epitaxial layer regulated and controlled by using the patterned sapphire substrate according to claim 1, wherein the high-temperature GaN primary epitaxial layer in the step 3) is formed by alternately growing a first GaN layer and a second GaN layer, and the number of alternate periods is 1-100.
6. The method for preparing a high-photoelectric-performance Al xGa1-x N epitaxial layer regulated by using a patterned sapphire substrate according to claim 5, wherein the growth conditions of the first GaN layer are as follows: the growth temperature is 1000-1050 ℃, the V/III ratio is 800-1800, the ammonia flow is 0.1-1000sccm, and the thickness is 50-200nm.
7. The method for preparing a high-photoelectric-performance Al xGa1-x N epitaxial layer regulated by using a patterned sapphire substrate according to claim 5, wherein the growth conditions of the second GaN layer are as follows: the growth temperature is 1050-1200 ℃, the ammonia flow is 1000-50000sccm, the V/III ratio is 4000-6500, and the thickness is 5-50nm.
8. The method for preparing the high-photoelectric-performance Al xGa1-x N epitaxial layer by using the patterned sapphire substrate as claimed in claim 1, wherein the TMAL flow rate used for the growth of the Al xGa1-x N epitaxial layer in the step 4) is 9.8-60 mu mol/min, the growth temperature is 1000-1100 ℃, and the growth thickness is 50-500nm.
9. The method for preparing a high photoelectric performance Al xGa1-x N epitaxial layer using patterned sapphire substrate regulation of claim 8, wherein the pressure of the Al xGa1-x N epitaxial layer growth reactor in step 4) is 32.5-98.2torr.
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