CN113990988B - GaN-based LED epitaxial growth method for improving crystallization quality - Google Patents

GaN-based LED epitaxial growth method for improving crystallization quality Download PDF

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CN113990988B
CN113990988B CN202111264835.4A CN202111264835A CN113990988B CN 113990988 B CN113990988 B CN 113990988B CN 202111264835 A CN202111264835 A CN 202111264835A CN 113990988 B CN113990988 B CN 113990988B
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CN113990988A (en
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徐平
胡耀武
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Xiangneng Hualei Optoelectrical Co Ltd
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
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    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
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    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
    • H01L33/0075—Processes for devices with an active region comprising only III-V compounds comprising nitride compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/04—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction
    • H01L33/06—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction within the light emitting region, e.g. quantum confinement structure or tunnel barrier
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    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/26—Materials of the light emitting region
    • H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
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Abstract

The application discloses a GaN-based LED epitaxial growth method for improving crystallization quality, which comprises the following steps: pre-paving Al, sequentially growing a pressure gradient AlN layer and Al on a sapphire substrate 0.45 Ga 0.25 N layer, growth temperature gradual change AlN layer, growth Al 0.25 Ga 0.75 N layer, growing constant temperature and constant pressure AlN layer and growing Al 0.15 Ga 0.85 The method comprises the steps of growing an N layer, growing an undoped GaN layer, growing an Si-doped N-type GaN layer, periodically growing an active layer MQW, growing a P-type AlGaN layer, growing an Mg-doped P-type GaN layer, and cooling. According to the method, the dislocation density of the material can be reduced, the crystallization quality of the epitaxial layer is improved, the warping and cracking of the epitaxial wafer are reduced, and the luminous efficiency and antistatic capability of the LED are improved.

Description

GaN-based LED epitaxial growth method for improving crystallization quality
Technical Field
The invention relates to the technical field of GaN-based LED epitaxial wafer growth, in particular to a GaN-based LED epitaxial growth method for improving crystallization quality.
Background
The currently commonly used method for growing GaN materials is to pattern on a sapphire substrate. Sapphire crystal is one of the best substrate materials for growing a third-generation semiconductor material GaN epitaxial layer, and the single crystal preparation process is mature. GaN is a base material for manufacturing a blue light LED, wherein the substrate material sapphire of the GaN epitaxial layer has the same structure as a GaN crystal (hexagonal symmetrical wurtzite crystal structure), the lattice mismatch degree with the GaN reaches 13%, the high dislocation density of the GaN epitaxial layer is easily caused, and AlN or low-temperature GaN epitaxial layer or SiO is added on the sapphire substrate 2 Layers, etc., can reduce the dislocation density of the GaN epitaxial layer.
The sapphire and the GaN have larger lattice mismatch (13-16%) and thermal mismatch, so that the density of the mismatch dislocation in the GaN epitaxial layer is higher (10) 10 cm -2 ) The quality of the GaN epitaxial layer and thus the device quality (luminous efficiency, drain electrode, lifetime, etc.) are affected.
The conventional method adopts a low-temperature buffer layer, and improves the crystal quality of the GaN epitaxial layer by adjusting the nitridation of the sapphire substrate, the growth temperature of the low-temperature buffer layer, the thickness of the buffer layer and the like. However, since the low temperature buffer layer still belongs to heteroepitaxy, its enhanced crystal quality is limited. In addition, because of the large lattice mismatch between the epitaxial film layers, the epitaxial crystal film is always stressed in the growth process, so that the epitaxial wafer is bent, warped and even cracked.
Disclosure of Invention
In view of the above, the present invention provides an LED epitaxial growth method for improving the crystallization quality, comprising the steps of:
performing pre-paving Al treatment on the sapphire substrate, wherein,
the pre-paving Al treatment comprises the following steps: controlling the pressure of the reaction cavity at 200-280mbar, controlling the temperature of the reaction cavity at 1000-1020 ℃, and introducing H 2 As carrier gas, simultaneously introducing TMAL source to perform pre-paving Al treatment for 50-60s, wherein the flow of TMAL is controlled to gradually increase from 80sccm to 120sccm in the pre-paving Al treatment process;
sequentially growing a pressure gradient AlN layer and Al on the sapphire substrate 0.45 Ga 0.25 N layer, growth temperature gradual change AlN layer, growth Al 0.25 Ga 0.75 N layer, growing constant temperature and constant pressure AlN layer and growing Al 0.15 Ga 0.85 An N layer, wherein,
the growth pressure gradient AlN layer comprises: controlling the growth temperature at 900-920 ℃, controlling the pressure of the reaction cavity at 220mbar, and introducing NH 3 、N 2 And TMAL, grow the pressure gradual change AlN layer with thickness D1 of 80-100nm on the said sapphire substrate, control the reaction chamber pressure to gradually reduce from 220mbar to 110mbar in the course of growing;
the grown Al 0.45 Ga 0.25 The N layer comprises: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 110mbar, and introducing NH 3 、N 2 TMGa and TMAL, and growing Al with the thickness of 120-140nm on the pressure gradient AlN layer 0.45 Ga 0.25 An N layer in which the molar composition of Al is 45%;
the growth temperature gradual change AlN layer comprises: maintaining the pressure of the reaction cavity to be 110mbar unchanged, and introducing NH into the reaction cavity 3 、N 2 And TMAL at the Al 0.45 Ga 0.25 The growth thickness D2 on the N layer isIn the growth process, the growth temperature of the 160-200nm AlN layer is controlled to gradually rise from 1020 ℃ to 1150 ℃ and then gradually drop from 1150 ℃ to 1100 ℃, wherein d2=2d1;
the grown Al 0.25 Ga 0.75 The N layer comprises: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 110mbar, and introducing NH 3 、N 2 TMGa and TMAL, and growing Al with the thickness of 120-140nm on the temperature gradient AlN layer 0.25 Ga 0.75 An N layer wherein the molar composition of Al is 25%;
the growing of the constant temperature and constant pressure AlN layer comprises the following steps: the growth temperature is increased to 900 ℃, the pressure of the reaction cavity is increased to 130mbar, and NH is introduced 3 、N 2 And TMAL at the Al 0.25 Ga 0.75 Growing a constant-temperature and constant-pressure AlN layer with the thickness D3 of 240-300nm on the N layer, and controlling the pressure and the temperature of a reaction cavity to be unchanged in the growing process, wherein d3=3d1;
the grown Al 0.15 Ga 0.85 The N layer comprises: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 130mbar unchanged, and introducing NH 3 、N 2 TMGa and TMAL, and Al with the thickness of 120-140nm is grown on the constant temperature and constant pressure AlN layer 0.15 Ga 0.85 An N layer wherein the molar composition of Al is 15%;
growing an undoped GaN layer;
growing an N-type GaN layer doped with Si;
periodically growing an active layer MQW;
growing a P-type AlGaN layer;
growing a P-type GaN layer doped with Mg;
and (5) cooling.
Preferably, the undoped GaN layer is grown, further, the temperature is raised to 1000-1200 ℃, the pressure of the reaction cavity is maintained at 150-300mbar, and NH with the flow rate of 30000-40000sccm is introduced 3 200-400sccm TMGa, 100-130L/min H 2 At the Al 0.15 Ga 0.85 And continuously growing an undoped GaN layer with the thickness of 2-4 mu m on the N layer.
Preferably, the growth is doped with SiThe N-type GaN layer is prepared by maintaining the pressure of the reaction cavity at 150-300mbar, maintaining the temperature at 1000-1100 deg.C, and introducing NH with flow of 40-60L/min 3 200-300sccm TMGa, 50-90L/min H 2 SiH of 20-50sccm 4 Continuously growing an N-type GaN layer doped with Si with the concentration of 5E+18-1E+19atoms/cm, wherein the N-type GaN layer is doped with Si with the concentration of 2-4 mu m, on the undoped GaN layer 3 。
Preferably, the periodically grown active layer MQW, further,
maintaining the pressure of the reaction cavity at 300-400mbar and the temperature at 720 ℃, and introducing NH with the flow rate of 50000-70000sccm 3 20-40sccm TMGa, 10000-15000sccm TMIn and 100-130L/min N 2 Growing an InGaN well layer doped with In and having a thickness of 3 nm;
raising the temperature to 800 ℃, keeping the pressure of the reaction cavity at 300-400mbar, and introducing NH with the flow rate of 50000-70000sccm 3 TMGa 20-100sccm and N100-130L/min 2 Growing a GaN barrier layer of 10 nm;
and repeatedly and alternately growing the InGaN well layer and the GaN barrier layer to obtain the InGaN/GaN multi-quantum well light-emitting layer, wherein the number of the alternate growth cycles of the InGaN well layer and the GaN barrier layer is 7-13.
Preferably, the growth of the P-type AlGaN layer is further that the temperature is raised to 900-1000 ℃, the pressure of the reaction cavity is maintained at 200-400mbar, the P-type AlGaN layer with 20-50nm is continuously grown on the MQW of the active layer, and the Al doping concentration is 1E+20-3E+20atoms/cm 3 Mg doping concentration 5E+18-1E+19atoms/cm 3 。
Preferably, the growing of the Mg-doped P-type GaN layer is further that the temperature is raised to 930-950 ℃, the pressure of the reaction cavity is maintained at 200-600mbar, and a 100-300nm Mg-doped P-type GaN layer is continuously grown on the P-type AlGaN layer, and the Mg doping concentration is 1E+19-1E+20atoms/cm 3 。
Preferably, the temperature is reduced to 700-800 ℃, the temperature is kept for 20-30min, and then the furnace is cooled.
Compared with the prior art, the LED epitaxial growth method for improving the crystallization quality provided by the invention has the following beneficial effects:
1. the wettability between the sapphire substrate and AlN can be enhanced by pre-paving the Al on the sapphire substrate, and the mobility of Al atoms and N atoms on the surface of the sapphire substrate is enhanced, so that the transverse growth rate of the AlN island is accelerated, and the healing of AlN is facilitated. In the pre-paving Al treatment process, the flow of TMAL is controlled to be gradually increased, so that the surface of the sapphire substrate is completely covered with Al atoms and an Al atomic layer with regular arrangement is formed, migration of adsorbed Al atoms is promoted, the Al atoms are quickly migrated to vacancies, defect formation is prevented, and further the crystal quality of the epitaxial AlN thin film at the later stage is improved.
2. By alternately growing three groups of AlN layers and AlGaN layers, the epitaxial wafer can be better matched with a substrate, has smaller lattice mismatch degree, can enable epitaxial atoms to be uniformly filled upwards, can release internal stress of the wafer, blocks upward extension of defects when the epitaxial wafer is directly and parallelly pushed upwards, reduces dislocation density, improves crystal quality, and can reduce warping of the epitaxial wafer and avoid occurrence of cracks.
3. The growth pressure gradual change AlN layer controls the pressure gradual change of the reaction cavity to be reduced, at the moment, the interface layer of the reaction between TMAL and ammonia reaches the surface of the sapphire substrate to carry out nucleation and crystallization growth, which is favorable for promoting GaN nucleation and simultaneously generating transverse and longitudinal growth, so that the GaN epitaxial layer has better crystallization quality.
4. In the process of growing the AlN layer with gradual change of the temperature, the gradual change of the growth temperature is controlled, and then the gradual change of the growth temperature is controlled, because the mobility of Al atoms is also improved along with the increase of the temperature, the grain size of AlN is reduced, the nucleation density of the grain is increased, the AlN layer further grows in a two-dimensional transverse direction, the roughness is reduced, and the GaN film obtained by epitaxy under the condition is flattest and bright, and the crystallization quality is higher. However, with the excessively high temperature, ga atoms can diffuse in the A1N buffer layer to form a certain interface layer, so that the crystal quality of the film is deteriorated, and the gradual reduction of the growth temperature is controlled, so that the deterioration of the crystal quality of the film can be avoided, and the improvement of the crystal quality of the material is facilitated.
5. By controlling the regular increase of the thickness of the three-layer AlN film, a certain compressive stress is introduced to partially offset the tensile stress generated between GaN and the sapphire substrate due to the large difference of thermal expansion coefficients, so that the problem of cracking of the GaN surface is relieved to a certain extent, and meanwhile, the defect generated by dislocation can be reduced, so that the crystallization quality of the GaN epitaxial layer is improved.
6. The crystallization quality of the GaN material can be improved by introducing three Al-component stepwise decreasing AlGaN layers, because the atomic radius between Ga atoms and Al atoms is greatly different, and meanwhile, when the AlGaN layer is grown by MOCVD, the atoms are not in ideal model arrangement but are in random arrangement, the content of the Al components is controlled to decrease, so that Al can be formed 0.25 Ga 0.75 N layer and Al 0.15 Ga 0.85 The lattice constant of the N layer is larger than that of the GaN layer, so that the effect of inhibiting dislocation is achieved, and the crystallization quality of the GaN layer is better.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and do not constitute a limitation on the invention. In the drawings:
fig. 1 is a schematic structural diagram of an LED epitaxy prepared in embodiment 1;
fig. 2 is a schematic structural diagram of the LED epitaxy prepared in comparative example 1;
wherein, 1, a sapphire substrate, 2, a pressure gradient AlN layer, 3, al 0.45 Ga 0.25 N layer, 4, alN layer with gradual temperature change, 5, al 0.25 Ga 0.75 N layer, 6, constant temperature and constant pressure AlN layer, 7, al 0.15 Ga 0.85 The GaN-based light emitting diode comprises an N layer, an 8 undoped GaN layer, a 9N-type GaN layer, a 10 multi-quantum well layer, an 11 AlGaN electron blocking layer, a 12P-type GaN layer, a 101 InGaN well layer, a 102 GaN barrier layer, a 13 low-temperature GaN buffer layer.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It should be noted that the embodiments described are merely some, but not all embodiments of the invention and are merely illustrative in nature and in no way serve as any limitation to the invention, its application, or uses. The scope of the present application is defined by the appended claims.
Example 1:
referring to fig. 1, an embodiment of a method for LED epitaxial growth for improving the crystallization quality according to the present application is shown, which includes:
step 1, pre-paving Al on a sapphire substrate 1, specifically, controlling the pressure of a reaction cavity to be 200-280mbar, controlling the temperature of the reaction cavity to be 1000-1020 ℃, and introducing H 2 And (3) taking the mixture as carrier gas, and simultaneously introducing a TMAL source to perform pre-paving Al treatment for 50-60s, wherein the flow of the TMAL is controlled to gradually increase from 80sccm to 120sccm in the pre-paving Al treatment process.
Step 2, sequentially growing a pressure gradient AlN layer 2 and Al on the sapphire substrate 0.45 Ga 0.25 N layer 3, growth temperature gradual change AlN layer 4 and growth Al 0.25 Ga 0.75 N layer 5, constant temperature and constant pressure AlN layer 6 and grown Al 0.15 Ga 0.85 N layer 7:
the growth pressure gradient AlN layer 2 comprises: controlling the growth temperature at 900-920 ℃, controlling the pressure of the reaction cavity at 220mbar, and introducing NH 3 、N 2 And TMAL, growing a pressure gradual change AlN layer 2 with the thickness D1 of 80-100nm on the sapphire substrate 1, and controlling the pressure of a reaction cavity to gradually decrease from 220mbar to 110mbar in the growth process;
the grown Al 0.45 Ga 0.25 The N layer 3 includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 110mbar, and introducing NH 3 、N 2 TMGa and TMAL, and growing Al with the thickness of 120-140nm on the pressure gradient AlN layer 2 0.45 Ga 0.25 N layer 3, wherein the molar composition of Al is 45%;
the growth temperature gradient AlN layer 4 comprises: maintaining the pressure of the reaction cavity to be 110mbar unchanged, and introducing NH into the reaction cavity 3 、N 2 And TMAL at the Al 0.45 Ga 0.25 Growing a temperature gradual change AlN layer 4 with the thickness D2 of 160-200nm on the N layer 3, and gradually increasing the growth temperature from 1020 ℃ to 1150 ℃ in the growth processControlling the growth temperature to gradually decrease from 1150 ℃ to 1100 ℃ again, wherein d2=2d1;
the grown Al 0.25 Ga 0.75 The N layer 5 includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 110mbar, and introducing NH 3 、N 2 TMGa and TMAL, and growing Al with the thickness of 120-140nm on the temperature gradient AlN layer 4 0.25 Ga 0.75 N layer 5, wherein the molar composition of Al is 25%;
the growing of the constant temperature and constant pressure AlN layer 6 comprises: the growth temperature is increased to 900 ℃, the pressure of the reaction cavity is increased to 130mbar, and NH is introduced 3 、N 2 And TMAL at the Al 0.25 Ga 0.75 Growing a constant temperature and constant pressure AlN layer 6 with the thickness D3 of 240-300nm on the N layer 5, and controlling the pressure and the temperature of a reaction cavity to be unchanged in the growing process, wherein d3=3d1;
the grown Al 0.15 Ga 0.85 The N layer 7 includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 130mbar unchanged, and introducing NH 3 、N 2 TMGa and TMAL, and Al with the thickness of 120-140nm is grown on the constant temperature and constant pressure AlN layer 6 0.15 Ga 0.85 N layer 7, wherein the molar composition of Al is 15%;
step 3, growing an undoped GaN layer 8: raising the temperature to 1000-1200 ℃, maintaining the pressure of the reaction cavity at 150-300mbar, and introducing NH with the flow rate of 30000-40000sccm 3 200-400sccm TMGa, 100-130L/min H 2 At the Al 0.15 Ga 0.85 An undoped GaN layer 8 of 2-4 μm is continuously grown on the N layer 7.
Step 4, growing an N-type GaN layer 9 doped with Si: maintaining the pressure of the reaction cavity at 150-300mbar, maintaining the temperature at 1000-1100 ℃, and introducing NH with the flow rate of 40-60L/min 3 200-300sccm TMGa, 50-90L/min H 2 SiH of 20-50sccm 4 Continuously growing an N-type GaN layer 9 doped with Si with the concentration of 5E+18-1E+19atoms/cm and 2-4 mu m on the undoped GaN layer 8 3 。
Step 5, periodically growing an active layer MQW10:
maintaining the pressure of the reaction cavity at 300-400mbar and the temperature at 720 DEG CIntroducing NH with flow rate of 50000-70000sccm 3 20-40sccm TMGa, 10000-15000sccm TMIn and 100-130L/min N 2 Growing an InGaN well layer 101 doped with In and having a thickness of 3 nm;
raising the temperature to 800 ℃, keeping the pressure of the reaction cavity at 300-400mbar, and introducing NH with the flow rate of 50000-70000sccm 3 TMGa 20-100sccm and N100-130L/min 2 Growing a 10nm GaN barrier layer 102;
and repeatedly and alternately growing the InGaN well layer 101 and the GaN barrier layer 102 to obtain the InGaN/GaN multi-quantum well light-emitting layer, wherein the number of the alternately growing periods of the InGaN well layer 101 and the GaN barrier layer 102 is 7-13.
Step 6, growing a P-type AlGaN layer 11: raising the temperature to 900-1000 ℃, maintaining the pressure of the reaction cavity at 200-400mbar, continuously growing a 20-50nm P-type AlGaN layer 11 on the active layer MQW10, and doping Al with concentration of 1E+20-3E+20atoms/cm 3 Mg doping concentration 5E+18-1E+19atoms/cm 3 。
Step 7, growing a P-type GaN layer 12 doped with Mg: raising the temperature to 930-950 ℃, maintaining the pressure of the reaction cavity at 200-600mbar, continuously growing a 100-300nm magnesium doped P-type GaN layer 12 on the P-type AlGaN layer 11, wherein the doping concentration of Mg is 1E+19-1E+20atoms/cm 3 。
Step 8, cooling: cooling to 700-800 ℃, preserving heat for 20-30min, and then cooling in a furnace.
Comparison experiment:
the following is a conventional GaN-based LED epitaxial growth method (the epitaxial structure diagram is shown in FIG. 2), and the specific steps are as follows:
1. the sapphire substrate 1 is treated at high temperature for 5-10 minutes under the hydrogen atmosphere of which the reaction cavity pressure is maintained at 100-150mbar at 1000-1200 ℃.
2. Cooling to 550-650deg.C, maintaining the pressure of the reaction chamber at 400-600mbar, and introducing NH with flow rate of 10000-20000sccm 3 50-100sccm TMGa, 100-130L/min H 2 And growing a low-temperature buffer layer GaN13 with the thickness of 20-50nm on the sapphire substrate.
3. Raising the temperature to 1000-1200 ℃, maintaining the pressure of the reaction cavity at 150-300mbar, and introducing NH with the flow rate of 30000-40000sccm 3 200-400sccm TMGa, 100-130L/min H 2 Continuously growing an undoped GaN layer 8 with the thickness of 2-4 mu m;
4. continuously growing an N-type GaN layer 9 doped with Si, wherein the doping concentration of Si is 5E+18-1E+19atoms/cm 3 The total thickness is controlled to be 2-4 μm.
5. The active layer MQW10 is grown periodically, comprising the steps of,
maintaining the pressure of the reaction cavity at 300-400mbar and the temperature at 720 ℃, and introducing NH with the flow rate of 50000-70000sccm 3 20-40sccm TMGa, 10000-15000sccm TMIn and 100-130L/min N 2 Growing an InGaN well layer 101 doped with In and having a thickness of 3 nm;
raising the temperature to 800 ℃, keeping the pressure of the reaction cavity at 300-400mbar, and introducing NH with the flow rate of 50000-70000sccm 3 TMGa 20-100sccm and N100-130L/min 2 Growing a 10nm GaN barrier layer 102;
and repeatedly and alternately growing the InGaN well layer 101 and the GaN barrier layer 102 to obtain the InGaN/GaN multi-quantum well light-emitting layer, wherein the number of the alternately growing periods of the InGaN well layer 101 and the GaN barrier layer 102 is 7-13.
6. Then the temperature is increased to 900-1000 ℃, the pressure of the reaction cavity is maintained at 200-400mbar, the P-type AlGaN layer 11 with 20-50nm is continuously grown, and the Al doping concentration is 1E+20-3E+20atoms/cm 3 Mg doping concentration 5E+18-1E+19atoms/cm 3 。
7. Then the temperature is increased to 930-950 ℃, the pressure of the reaction cavity is maintained at 200-600mbar, a 100-300nm magnesium doped P-type GaN layer 12 is continuously grown, and the doping concentration of Mg is 1E+19-1E+20atoms/cm 3 。
8. Finally cooling to 700-800 ℃, preserving heat for 20-30min, and then cooling in a furnace.
A group of epitaxial wafer samples W1 were grown using the growth method provided by the invention, and a group of epitaxial wafer samples W2 were grown using the growth method of the conventional process. The epitaxial wafer sample W1 was fabricated as a 254 μm×686 μm chip sample C1 according to the standard process on the production line, and the epitaxial wafer sample W2 was fabricated as a 254 μm×686 μm chip sample C2 according to the standard process on the production line.
The crystallization quality of the GaN epitaxial wafer samples was characterized by using a high resolution X-ray diffractometer (HRXRD) model D8 Discover, and the photoelectric properties of the chip samples were tested using a semi-automatic crystal circle measuring machine model LEDA-8f p7202, as shown in table 1:
TABLE 1 FWHM (full width at half maximum) and dislocation density of XRD rocking curve of sample W1W 2
By analysing table 1, the following can be concluded: compared with the sample W2, the screw dislocation density and the edge dislocation density of the sample W1 are obviously reduced, and the half width is smaller, so that the method can effectively improve the crystal quality of the epitaxial film. In addition, the appearance yield of the samples W1 and W2 is counted, the proportion of cracks on the surface of the sample W2 is 0.7%, and the proportion of cracks on the surface of the sample W1 is 0.2%, which shows that the method can obviously improve the appearance condition of the surface of the epitaxial wafer and the yield of the product.
The warping degree BOW value data (um) of the epitaxial wafer samples W1 and W2 are counted, the average value of the warping degree of the W1 sample is 5.1um, the average value of the warping degree of the W2 sample is 6.4um, and the warping degree of the LED epitaxial wafer sample manufactured by the method is obviously small, so that the method can obviously reduce the warping of the epitaxial wafer.
In order to clarify the influence of the crystal quality of the GaN-based epitaxial wafer grown by the method and the traditional method on the photoelectric parameters of the LED device, a sample W1 and a sample W2 are respectively manufactured into chips. Specifically, sample W1 was fabricated into a chip to obtain a chip sample C1 having a size of 254 μm×686 μm; sample W2 was fabricated into a chip to obtain a chip sample C2 having a size of 254 μm by 686. Mu.m; the average value of all the core photoelectric parameters was determined by testing the luminous power (LOP) at 150mA in the forward direction, the leakage current (IR) at-5V in the reverse direction, and the antistatic ability (ESD pass rate) at 6000V in the Human Body Mode (HBM), as shown in table 2:
TABLE 2 Main photoelectric parameter test values for chip samples C1 and C2
By analysing table 2, the following can be concluded: the chip sample manufactured by the growth method provided by the invention has high luminous power, obviously small electric leakage and high antistatic yield.
According to the embodiments, the beneficial effects of the application are as follows:
1. the wettability between the sapphire substrate and AlN can be enhanced by pre-paving the Al on the sapphire substrate, and the mobility of Al atoms and N atoms on the surface of the sapphire substrate is enhanced, so that the transverse growth rate of the AlN island is accelerated, and the healing of AlN is facilitated. In the pre-paving Al treatment process, the flow of TMAL is controlled to be gradually increased, so that the surface of the sapphire substrate is completely covered with Al atoms and an Al atomic layer with regular arrangement is formed, migration of adsorbed Al atoms is promoted, the Al atoms are quickly migrated to vacancies, defect formation is prevented, and further the crystal quality of the epitaxial AlN thin film at the later stage is improved.
2. By alternately growing three groups of AlN layers and AlGaN layers, the epitaxial wafer can be better matched with a substrate, has smaller lattice mismatch degree, can enable epitaxial atoms to be uniformly filled upwards, can release internal stress of the wafer, blocks upward extension of defects when the epitaxial wafer is directly and parallelly pushed upwards, reduces dislocation density, improves crystal quality, and can reduce warping of the epitaxial wafer and avoid occurrence of cracks.
3. The growth pressure gradual change AlN layer controls the pressure gradual change of the reaction cavity to be reduced, at the moment, the interface layer of the reaction between TMAL and ammonia reaches the surface of the sapphire substrate to carry out nucleation and crystallization growth, which is favorable for promoting GaN nucleation and simultaneously generating transverse and longitudinal growth, so that the GaN epitaxial layer has better crystallization quality.
4. In the process of growing the AlN layer with gradual change of the temperature, the gradual change of the growth temperature is controlled, and then the gradual change of the growth temperature is controlled, because the mobility of Al atoms is also improved along with the increase of the temperature, the grain size of AlN is reduced, the nucleation density of the grain is increased, the AlN layer further grows in a two-dimensional transverse direction, the roughness is reduced, and the GaN film obtained by epitaxy under the condition is flattest and bright, and the crystallization quality is higher. However, with the excessively high temperature, ga atoms can diffuse in the A1N buffer layer to form a certain interface layer, so that the crystal quality of the film is deteriorated, and the gradual reduction of the growth temperature is controlled, so that the deterioration of the crystal quality of the film can be avoided, and the improvement of the crystal quality of the material is facilitated.
5. By controlling the regular increase of the thickness of the three-layer AlN film, a certain compressive stress is introduced to partially offset the tensile stress generated between GaN and the sapphire substrate due to the large difference of thermal expansion coefficients, so that the problem of cracking of the GaN surface is relieved to a certain extent, and meanwhile, the defect generated by dislocation can be reduced, so that the crystallization quality of the GaN epitaxial layer is improved.
6. The crystallization quality of the GaN material can be improved by introducing three Al-component stepwise decreasing AlGaN layers, because the atomic radius between Ga atoms and Al atoms is greatly different, and meanwhile, when the AlGaN layer is grown by MOCVD, the atoms are not in ideal model arrangement but are in random arrangement, the content of the Al components is controlled to decrease, so that Al can be formed 0.25 Ga 0.75 N layer and Al 0.15 Ga 0.85 The lattice constant of the N layer is larger than that of the GaN layer, so that the effect of inhibiting dislocation is achieved, and the crystallization quality of the GaN layer is better.
While certain specific embodiments of the invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the invention. Although the invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the techniques described in the foregoing embodiments, or equivalents may be substituted for elements thereof. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (7)

1. The GaN-based LED epitaxial growth method for improving the crystallization quality is characterized by comprising the following steps of:
performing pre-paving Al treatment on the sapphire substrate, wherein,
the pre-paving Al treatment comprises the following steps: controlling the pressure of the reaction cavity at 200-280mbar, controlling the temperature of the reaction cavity at 1000-1020 ℃, and introducing H 2 As carrier gas, simultaneously introducing TMAL source to perform pre-paving Al treatment for 50-60s, wherein the flow of TMAL is controlled to gradually increase from 80sccm to 120sccm in the pre-paving Al treatment process;
sequentially growing a pressure gradient AlN layer and Al on the sapphire substrate 0.45 Ga 0.25 N layer, growth temperature gradual change AlN layer, growth Al 0.25 Ga 0.75 N layer, growing constant temperature and constant pressure AlN layer and growing Al 0.15 Ga 0.85 An N layer, wherein,
the growth pressure gradient AlN layer comprises: controlling the growth temperature at 900-920 ℃, controlling the pressure of the reaction cavity at 220mbar, and introducing NH 3 、N 2 And TMAL, grow the pressure gradual change AlN layer with thickness D1 of 80-100nm on the said sapphire substrate, control the reaction chamber pressure to gradually reduce from 220mbar to 110mbar in the course of growing;
the grown Al 0.45 Ga 0.25 The N layer comprises: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 110mbar, and introducing NH 3 、N 2 TMGa and TMAL, and growing Al with the thickness of 120-140nm on the pressure gradient AlN layer 0.45 Ga 0.25 An N layer in which the molar composition of Al is 45%;
the growth temperature gradual change AlN layer comprises: maintaining the pressure of the reaction cavity to be 110mbar unchanged, and introducing NH into the reaction cavity 3 、N 2 And TMAL at the Al 0.45 Ga 0.25 Growing a temperature gradual change AlN layer with the thickness D2 of 160-200nm on the N layer, wherein the growth temperature is controlled to gradually rise from 1020 ℃ to 1150 ℃ and then gradually drop from 1150 ℃ to 1100 ℃ in the growth process, wherein D2＝2D1；
The grown Al 0.25 Ga 0.75 The N layer comprises: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 110mbar, and introducing NH 3 、N 2 TMGa and TMAL, and growing Al with the thickness of 120-140nm on the temperature gradient AlN layer 0.25 Ga 0.75 An N layer wherein the molar composition of Al is 25%;
the growing of the constant temperature and constant pressure AlN layer comprises the following steps: the growth temperature is increased to 900 ℃, the pressure of the reaction cavity is increased to 130mbar, and NH is introduced 3 、N 2 And TMAL at the Al 0.25 Ga 0.75 Growing a constant-temperature and constant-pressure AlN layer with the thickness D3 of 240-300nm on the N layer, and controlling the pressure and the temperature of a reaction cavity to be unchanged in the growing process, wherein d3=3d1;
the grown Al 0.15 Ga 0.85 The N layer comprises: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity to be 130mbar unchanged, and introducing NH 3 、N 2 TMGa and TMAL, and Al with the thickness of 120-140nm is grown on the constant temperature and constant pressure AlN layer 0.15 Ga 0.85 An N layer wherein the molar composition of Al is 15%;
growing an undoped GaN layer;
growing an N-type GaN layer doped with Si;
periodically growing an active layer MQW;
growing a P-type AlGaN layer;
growing a P-type GaN layer doped with Mg;
and (5) cooling.
2. The method for epitaxial growth of GaN-based LED with improved crystallization quality according to claim 1, wherein the undoped GaN layer is grown, further, the temperature is raised to 1000-1200 ℃, the pressure of the reaction chamber is maintained at 150-300mbar, and NH with flow rate of 30000-40000sccm is introduced 3 200-400sccm TMGa, 100-130L/min H 2 At the Al 0.15 Ga 0.85 And continuously growing an undoped GaN layer with the thickness of 2-4 mu m on the N layer.
3. A handle according to claim 1The epitaxial growth method of GaN-based LED with raised crystallization quality is characterized in that the growth of an N-type GaN layer doped with Si is further characterized in that the pressure of a reaction cavity is kept at 150-300mbar, the temperature is kept at 1000-1100 ℃, and NH with the flow rate of 40-60L/min is introduced 3 200-300sccm TMGa, 50-90L/min H 2 SiH of 20-50sccm 4 Continuously growing an N-type GaN layer doped with Si with the concentration of 5E+18-1E+19atoms/cm, wherein the N-type GaN layer is doped with Si with the concentration of 2-4 mu m, on the undoped GaN layer 3 。
4. The method for epitaxial growth of GaN-based LEDs with improved crystallization quality according to claim 1, wherein the periodically grown active layer MQW, further,
maintaining the pressure of the reaction cavity at 300-400mbar and the temperature at 720 ℃, and introducing NH with the flow rate of 50000-70000sccm 3 20-40sccm TMGa, 10000-15000sccm TMIn and 100-130L/min N 2 Growing an InGaN well layer doped with In and having a thickness of 3 nm;
raising the temperature to 800 ℃, keeping the pressure of the reaction cavity at 300-400mbar, and introducing NH with the flow rate of 50000-70000sccm 3 TMGa 20-100sccm and N100-130L/min 2 Growing a GaN barrier layer of 10 nm;
and repeatedly and alternately growing the InGaN well layer and the GaN barrier layer to obtain the InGaN/GaN multi-quantum well light-emitting layer, wherein the number of the alternate growth cycles of the InGaN well layer and the GaN barrier layer is 7-13.
5. The epitaxial growth method of GaN-based LED with improved crystallization quality according to claim 1, wherein the growth of the P-type AlGaN layer is further carried out by raising the temperature to 900-1000 ℃, maintaining the pressure of the reaction chamber at 200-400mbar, continuously growing the P-type AlGaN layer with 20-50nm on the MQW of the active layer, and doping Al with the concentration of 1E+20-3E+20atoms/cm 3 Mg doping concentration 5E+18-1E+19atoms/cm 3 。
6. The epitaxial growth method of GaN-based LED with improved crystallization quality according to claim 1, wherein the growing of the Mg-doped P-type GaN layer is further carried out by raising the temperature to 930-950 ℃, and the reaction chamberThe pressure is maintained at 200-600mbar, a 100-300nm magnesium doped P-type GaN layer is continuously grown on the P-type AlGaN layer, and the doping concentration of Mg is 1E+19-1E+20atoms/cm 3 。
7. The method for epitaxial growth of GaN-based LEDs of claim 1, wherein the cooling is further performed by cooling to 700-800 ℃, maintaining the temperature for 20-30min, and then furnace cooling.
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