CN113990988A - 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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CN113990988A
CN113990988A CN202111264835.4A CN202111264835A CN113990988A CN 113990988 A CN113990988 A CN 113990988A CN 202111264835 A CN202111264835 A CN 202111264835A CN 113990988 A CN113990988 A CN 113990988A
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CN113990988B (en
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徐平
胡耀武
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Xiangneng Hualei Optoelectrical Co Ltd
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    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier 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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    • H01L33/0075—Processes for devices with an active region comprising only III-V compounds comprising nitride compounds
    • H—ELECTRICITY
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    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier 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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    • H01L33/04—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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
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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-laying Al, growing AlN layer with gradually changed pressure and growing Al on sapphire substrate0.45Ga0.25N layer, AlN layer with gradually-changed growth temperature and Al layer0.25Ga0.75N layer, growth of constant temperature and constant pressure AlN layer and growth of Al0.15Ga0.85And the N layer grows an undoped GaN layer, a Si-doped N-type GaN layer, a periodically grown active layer MQW, a P-type AlGaN layer, a Mg-doped P-type GaN layer, and cooling. The method and the device can reduce the dislocation density of the material, improve the crystallization quality of the epitaxial layer, reduce the warping and cracks of the epitaxial wafer, and improve the luminous efficiency and the antistatic capacity of the LED.

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 the crystallization quality.
Background
The currently widely adopted GaN material growth method is patterning on a sapphire substrate. The sapphire crystal is the growth of a third generation semiconductor material GaN epitaxial layerOne of the best substrate materials, the single crystal production process thereof is mature. GaN is a substrate for manufacturing a blue LED, wherein the substrate material of the GaN epitaxial layer is sapphire with the same structure as the GaN crystal (hexagonal symmetrical wurtzite crystal structure) and has lattice mismatch with the GaN crystal up to 13%, which easily causes high dislocation density of the GaN epitaxial layer, therefore, AlN or low-temperature GaN epitaxial layer or SiO is added on the sapphire substrate2Layers, etc., which can reduce the dislocation density of the GaN epitaxial layers.
The large lattice mismatch (13-16%) and thermal mismatch between sapphire and GaN lead to a high (10-10%) misfit dislocation density in the GaN epitaxial layer10cm-2) And affects the quality of the GaN epitaxial layer and thus the device quality (light emission efficiency, drain electrode, lifetime, etc.).
The conventional method is to adopt a low-temperature buffer layer, and improve 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 is also heteroepitaxial, the improved crystal quality is limited. In addition, because of the large lattice mismatch among the epitaxial thin film layers, the epitaxial crystal thin film is always stressed in the growth process, and 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 crystal quality, including the steps of:
pre-Al-plating treatment is performed on a sapphire substrate, wherein,
the pre-laid Al treatment comprises the following steps: controlling the pressure of the reaction cavity at 200-280mbar, the temperature of the reaction cavity at 1000-1020 ℃, and introducing H2As a carrier gas, introducing a TMAl source to carry out pre-paving Al treatment for 50-60s, and gradually increasing the flow of the TMAl from 80sccm to 120sccm in the pre-paving Al treatment process;
growing a pressure-gradient AlN layer and growing Al on the sapphire substrate in sequence0.45Ga0.25N layer, AlN layer with gradually-changed growth temperature and Al layer0.25Ga0.75N layer, growth of constant temperature and constant pressure AlN layer and growth of Al0.15Ga0.85N layers of a plurality of N layers, wherein,
the growth pressure-graded AlN layer includes: controlling the growth temperature at 900-920 ℃, controlling the pressure of the reaction cavity at 220mbar, and introducing NH3、N2TMAl, growing a pressure gradient AlN layer with the thickness D1 of 80-100nm on the sapphire substrate, and gradually reducing the pressure of a reaction chamber from 220mba to 110mbar in the growth process;
the grown Al0.45Ga0.25The N layer includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity unchanged at 110mbar, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the pressure gradient AlN layer0.45Ga0.25An N layer, wherein the molar composition of Al is 45%;
the growth temperature graded AlN layer includes: keeping the pressure of the reaction cavity constant at 110mbar, and introducing NH into the reaction cavity3、N2And TMAl in the Al0.45Ga0.25Growing a temperature gradient AlN layer with the thickness D2 of 160-;
the grown Al0.25Ga0.75The N layer includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity unchanged at 110mbar, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the temperature-gradient AlN layer0.25Ga0.75An N layer, wherein the molar composition of Al is 25%;
the growth constant-temperature and constant-pressure AlN layer comprises: the growth temperature is increased to 900 ℃, the pressure of the reaction cavity is increased to 130mbar, NH is introduced3、N2And TMAl in the Al0.25Ga0.75Growing 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 the reaction cavity to be constant in the growth process, wherein D3 is 3D 1;
the grown Al0.15Ga0.85The N layer includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity at 130mba constant, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the constant-temperature and constant-pressure AlN layer0.15Ga0.85An 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 cooling.
Preferably, the undoped GaN layer is grown, further, the temperature is raised to 1000-3200-400sccm TMGa, 100-130L/min H2In said Al0.15Ga0.85And continuously growing an undoped GaN layer of 2-4 mu m on the N layer.
Preferably, the Si-doped N-type GaN layer is grown by further keeping the pressure of the reaction chamber at 150-3200-300sccm TMGa, 50-90L/min H2And 20-50sccm SiH4Continuously growing a 2-4 μm Si-doped N-type GaN layer on the undoped GaN layer, wherein the doping concentration of Si is 5E +18-1E +19atoms/cm3。
Preferably, the periodically grown active layer MQW, further,
keeping the pressure of the reaction cavity at 300-320-40sccm of TMGa, 10000-2Growing an In-doped InGaN well layer with the thickness of 3 nm;
raising the temperature to 800 ℃, keeping the pressure of the reaction cavity at 300-320-100sccm of TMGa and 100-130L/min of N2Growing a 10nm GaN barrier layer;
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 carried out by raising the temperature to 900-3Mg doping concentration of 5E +18-1E +19atoms/cm3。
Preferably, the growth of the Mg-doped P-type GaN layer is further carried out by raising the temperature to 930-3。
Preferably, the temperature is reduced to 800 ℃ 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 wetting property between the sapphire substrate and AlN can be enhanced by firstly pre-paving the sapphire substrate with Al, 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 AlN is favorably healed. The flow of TMAl is controlled to be gradually increased in the pre-laying Al treatment process, so that the surface of the sapphire substrate can completely cover Al atoms and form regularly arranged Al atom layers, the migration of adsorbed Al atoms is promoted, the Al atoms are rapidly migrated to vacant positions, the formation of defects is prevented, and the crystal quality of the later-stage epitaxial AlN thin film is improved.
2. Through carrying out the growth of three groups of AlN layers and aluminium gallium nitrogen layers in turn, can better match with the substrate, have less lattice mismatch degree, and can make epitaxial atom fill even upwards, epitaxial layer atom can release the piece internal stress, blocks the upwards extension of defect when direct parallel upwards passes, reduces dislocation density, improves crystal quality to can reduce epitaxial wafer warpage and avoid appearing the crackle.
3. The growth pressure gradient AlN layer controls the gradual reduction of the pressure of the reaction cavity, and at the moment, the interface layer where TMAl and ammonia react reaches the surface of the sapphire substrate so as to perform nucleation and crystal growth, thereby being beneficial to promoting GaN nucleation and simultaneously generating transverse and longitudinal growth, so that the GaN epitaxial layer obtains better crystallization quality.
4. In the process of growing the AlN layer with the gradually-changed growth temperature, the gradually-changed growth temperature is controlled to rise, then the gradually-changed growth temperature is controlled to fall, because the mobility of Al atoms is improved along with the rise of the temperature, the grain size of AlN is reduced, the nucleation density of grains is increased, the GaN film obtained by epitaxy is further grown transversely in two dimensions, the roughness is reduced, the GaN film obtained by epitaxy under the condition is the most flat and bright, and the crystallization quality is higher. However, with the over-high temperature, Ga atoms are diffused in the A1N buffer layer to form a certain interface layer, thereby deteriorating the crystal quality of the thin film.
5. By controlling the thickness of the three AlN thin films to be increased regularly, a certain compressive stress is introduced to partially offset the tensile stress generated between the GaN and the sapphire substrate due to large difference of thermal expansion coefficients, so that the problem of GaN surface cracking is relieved to a certain extent, and meanwhile, the defect generated by dislocation can be reduced, thereby improving the crystallization quality of the GaN epitaxial layer.
6. The reason why the crystal quality of the GaN material can be improved by introducing the three aluminum gallium nitrogen layers with the Al components gradually decreased is that the atomic radius difference between Ga atoms and Al atoms is large, and meanwhile, when the aluminum gallium nitrogen layers are grown by the MOCVD adopted by people, atoms are not arranged in an ideal model but are randomly arranged, the content of the Al components is controlled to be decreased gradually, so that the Al components can be enabled to be gradually decreased0.25Ga0.75N layer and Al0.15Ga0.85The 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 not to limit the invention. In the drawings:
FIG. 1 is a schematic structural view of an epitaxial LED prepared in example 1;
FIG. 2 is a schematic view of the epitaxial structure of the LED prepared in comparative example 1;
wherein, 1, sapphire substrate, 2, pressure gradient AlN layer, 3, Al0.45Ga0.25N layer, 4, AlN layer with gradual temperature change, 5, Al0.25Ga0.75N layer, 6 constant temperature and pressure AlN layer, 7 Al layer0.15Ga0.85The GaN-based low-temperature GaN buffer layer comprises an N layer, 8, an undoped GaN layer, 9, an N-type GaN layer, 10, a multi-quantum well layer, 11, an AlGaN electron barrier layer, 12, a P-type GaN layer, 101, an InGaN well layer, 102, a GaN barrier layer and 13 and a low-temperature GaN buffer layer.
Detailed Description
The technical solution 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 described embodiments are merely some embodiments, rather than all embodiments, of the invention and are merely illustrative in nature and in no way intended to limit the invention, its application, or uses. The protection scope of the present application shall be subject to the definitions of the appended claims.
Example 1:
referring to fig. 1, a specific embodiment of the method for epitaxial growth of an LED to improve the crystal quality according to the present application is shown, the method including:
step 1, pre-laying Al on the sapphire substrate 1, specifically, controlling the pressure of a reaction chamber at 200-2And (3) as a carrier gas, introducing a TMAl source at the same time to carry out pre-paving Al treatment for 50-60s, and gradually increasing the flow of the TMAl from 80sccm to 120sccm in the pre-paving Al treatment process.
Step 2, growing a pressure gradient AlN layer 2 and growing Al on the sapphire substrate in sequence0.45Ga0.25N layer 3, growth temperature gradient AlN layer 4, growth Al0.25Ga0.75N layer 5, constant temperature and pressure AlN layer 6 and growing Al0.15Ga0.85N layer 7:
the growth pressure-graded AlN layer 2 includes: will growThe temperature is controlled at 900 ℃ and 920 ℃, the pressure of the reaction cavity is 220mbar, NH is introduced3、N2TMAl, growing a pressure gradient AlN layer 2 with the thickness D1 of 80-100nm on the sapphire substrate 1, and gradually reducing the pressure of a reaction cavity from 220mba to 110mbar in the growth process;
the grown Al0.45Ga0.25 The N layer 3 includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity unchanged at 110mbar, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the pressure gradient AlN layer 20.45Ga0.25 An N layer 3, wherein the molar composition of Al is 45%;
the growth temperature-graded AlN layer 4 includes: keeping the pressure of the reaction cavity constant at 110mbar, and introducing NH into the reaction cavity3、N2And TMAl in the Al0.45Ga0.25Growing an AlN layer 4 with the thickness D2 of 160-200nm on the N layer 3, wherein the growth temperature is gradually increased from 1020 ℃ to 1150 ℃ in the growth process, and then the growth temperature is gradually decreased from 1150 ℃ to 1100 ℃, wherein D2 is 2D 1;
the grown Al0.25Ga0.75 The N layer 5 includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity unchanged at 110mbar, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the temperature gradient AlN layer 40.25Ga0.75 An N layer 5 in which the molar composition of Al is 25%;
the growth constant-temperature constant-pressure AlN layer 6 comprises: the growth temperature is increased to 900 ℃, the pressure of the reaction cavity is increased to 130mbar, NH is introduced3、N2And TMAl in the Al0.25Ga0.75Growing 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 the reaction cavity to be constant in the growing process, wherein D3 is 3D 1;
the grown Al0.15Ga0.85 The N layer 7 includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity at 130mba constant, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the constant-temperature and constant-pressure AlN layer 60.15Ga0.85 An N layer 7 in which Al has a molar composition of 15%;
step 3, growing an undoped GaN layer 8: the temperature is raised to 1000-3200-400sccm TMGa, 100-130L/min H2In said Al0.15Ga0.85An undoped GaN layer 8 of 2-4 μm is continuously grown on the N layer 7.
Step 4, growing the Si-doped N-type GaN layer 9: keeping the pressure of the reaction cavity at 150-3200-300sccm TMGa, 50-90L/min H2And 20-50sccm SiH4Continuously growing a 2-4 μm Si-doped N-type GaN layer 9 with a Si doping concentration of 5E +18-1E +19atoms/cm on the undoped GaN layer 83。
Step 5, periodically growing an active layer MQW 10:
keeping the pressure of the reaction cavity at 300-320-40sccm of TMGa, 10000-2Growing an In-doped InGaN well layer 101 with a thickness of 3 nm;
raising the temperature to 800 ℃, keeping the pressure of the reaction cavity at 300-320-100sccm of TMGa and 100-130L/min of N2Growing 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 alternate growth cycles of the InGaN well layer 101 and the GaN barrier layer 102 is 7-13.
And 6, growing a P-type AlGaN layer 11: raising the temperature to 900-3Mg doping concentration of 5E +18-1E +19atoms/cm3。
Step 7, growing a P-type GaN layer 12 doped with Mg: raising the temperature to 930-The P-type GaN layer 12 of (1E +19-1E +20 atoms/cm) Mg doping concentration3。
Step 8, cooling: cooling to 800 ℃ at 700 ℃, preserving the heat for 20-30min, and then cooling in the furnace.
Comparative experiment:
the following is a GaN-based LED epitaxial growth method (an epitaxial structure diagram is shown in figure 2) in the traditional process, and the specific steps are as follows:
1. the sapphire substrate 1 is processed at high temperature for 5-10 minutes under the hydrogen atmosphere with the reaction chamber pressure of 100-1200 ℃ and the reaction chamber pressure of 150 mbar.
2. Cooling to 550-650 deg.C, maintaining the pressure in the reaction chamber at 400-600mbar, and introducing 10000-20000sccm NH3TMGa 50-100sccm, H100-130L/min2And growing a low-temperature buffer layer GaN13 with the thickness of 20-50nm on the sapphire substrate.
3. The temperature is raised to 1000-3200-400sccm TMGa, 100-130L/min H2Continuously 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 with a doping concentration of 5E +18-1E +19atoms/cm3The total thickness is controlled to be 2-4 μm.
5. The active layer MQW10 is periodically grown, including the steps,
keeping the pressure of the reaction cavity at 300-320-40sccm of TMGa, 10000-2Growing an In-doped InGaN well layer 101 with a thickness of 3 nm;
raising the temperature to 800 ℃, keeping the pressure of the reaction cavity at 300-320-100sccm of TMGa and 100-130L/min of N2Growing 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 alternate growth cycles of the InGaN well layer 101 and the GaN barrier layer 102 is 7-13.
6. Then the temperature is raised to 900-1000 ℃,the pressure of the reaction chamber is maintained at 200-400mbar, the P-type AlGaN layer 11 with the thickness of 20-50nm is continuously grown, and the Al doping concentration is 1E +20-3E +20atoms/cm3Mg doping concentration of 5E +18-1E +19atoms/cm3。
7. The temperature is raised to 930-3。
8. Finally, the temperature is reduced to 700 ℃ and 800 ℃, the temperature is preserved for 20-30min, and then the furnace is cooled.
A group of epitaxial wafer samples W1 were grown using the growth method provided by the present invention, and a group of epitaxial wafer samples W2 were grown using the growth method of the conventional process. The epitaxial wafer sample W1 is made into a chip sample C1 with the size of 254 microns multiplied by 686 microns according to the standard process on the production line, and the epitaxial wafer sample W2 is made into a chip sample C2 with the size of 254 microns multiplied by 686 microns according to the standard process on the production line.
The crystal quality of the GaN epitaxial wafer samples was characterized using a high resolution X-ray diffractometer (HRXRD) model D8 Discover, and the photoelectric properties of the chip samples were tested using a semi-integrating sphere full-automatic wafer spot tester model LEDA-8F P7202, as shown in table 1:
TABLE 1 FWHM (full width at half maximum) and dislocation density of XRD rocking curve for sample W1W 2
Figure BDA0003326636490000091
By analyzing table 1, the following conclusions can be drawn: compared with the sample W2, the threading dislocation density and the edge dislocation density of the sample W1 are both obviously reduced, and the half-height width is smaller, which shows that the method of the invention can effectively improve the crystal quality of the epitaxial thin film. In addition, statistics on the appearance yield of the samples W1 and W2 show that the proportion of cracks existing on the surface of the W2 sample is 0.7%, and the proportion of cracks existing on the surface of the W1 sample is 0.2%, which shows that the method can obviously improve the appearance condition of the surface of the epitaxial wafer and improve the product yield.
The warping BOW value data (um) of the epitaxial wafer samples W1 and W2 are counted, the mean value of the warping of the W1 sample is 5.1um, the mean value of the warping of the W2 sample is 6.4um, and the warping degree of the LED epitaxial wafer sample manufactured by the method is obviously small, which shows that the warping degree of the epitaxial wafer can be obviously reduced by the method.
In order to clarify the influence of the crystal quality of the GaN-based epitaxial wafer grown by the method of the present invention and the conventional method on the photoelectric parameters of the LED device, samples W1 and W2 were fabricated as chips, respectively. Specifically, the sample W1 was fabricated into a chip, and a chip sample C1 of 254 μm × 686 μm in size was obtained; preparing a chip from the sample W2 to obtain a chip sample C2 with the size of 254 microns multiplied by 686 microns; the luminous power (LOP) is tested by using a point measuring machine under the forward direction of 150mA, the leakage current (IR) is tested under the reverse direction of-5V, the antistatic capability (ESD passing rate) is tested under the Human Body Mode (HBM) of 6000V, and the average value of all core particle photoelectric parameters is obtained, as shown in Table 2:
TABLE 2 test values for the main optoelectronic parameters of chip samples C1 and C2
Figure BDA0003326636490000092
Figure BDA0003326636490000101
By analyzing table 2, the following conclusions can be drawn: the chip sample manufactured by the growth method provided by the invention has high luminous power, obvious small electric leakage and high antistatic yield.
According to the embodiments, the application has the following beneficial effects:
1. the wetting property between the sapphire substrate and AlN can be enhanced by firstly pre-paving the sapphire substrate with Al, 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 AlN is favorably healed. The flow of TMAl is controlled to be gradually increased in the pre-laying Al treatment process, so that the surface of the sapphire substrate can completely cover Al atoms and form regularly arranged Al atom layers, the migration of adsorbed Al atoms is promoted, the Al atoms are rapidly migrated to vacant positions, the formation of defects is prevented, and the crystal quality of the later-stage epitaxial AlN thin film is improved.
2. Through carrying out the growth of three groups of AlN layers and aluminium gallium nitrogen layers in turn, can better match with the substrate, have less lattice mismatch degree, and can make epitaxial atom fill even upwards, epitaxial layer atom can release the piece internal stress, blocks the upwards extension of defect when direct parallel upwards passes, reduces dislocation density, improves crystal quality to can reduce epitaxial wafer warpage and avoid appearing the crackle.
3. The growth pressure gradient AlN layer controls the gradual reduction of the pressure of the reaction cavity, and at the moment, the interface layer where TMAl and ammonia react reaches the surface of the sapphire substrate so as to perform nucleation and crystal growth, thereby being beneficial to promoting GaN nucleation and simultaneously generating transverse and longitudinal growth, so that the GaN epitaxial layer obtains better crystallization quality.
4. In the process of growing the AlN layer with the gradually-changed growth temperature, the gradually-changed growth temperature is controlled to rise, then the gradually-changed growth temperature is controlled to fall, because the mobility of Al atoms is improved along with the rise of the temperature, the grain size of AlN is reduced, the nucleation density of grains is increased, the GaN film obtained by epitaxy is further grown transversely in two dimensions, the roughness is reduced, the GaN film obtained by epitaxy under the condition is the most flat and bright, and the crystallization quality is higher. However, with the over-high temperature, Ga atoms are diffused in the A1N buffer layer to form a certain interface layer, thereby deteriorating the crystal quality of the thin film.
5. By controlling the thickness of the three AlN thin films to be increased regularly, a certain compressive stress is introduced to partially offset the tensile stress generated between the GaN and the sapphire substrate due to large difference of thermal expansion coefficients, so that the problem of GaN surface cracking is relieved to a certain extent, and meanwhile, the defect generated by dislocation can be reduced, thereby improving the crystallization quality of the GaN epitaxial layer.
6. The crystal quality of the GaN material can be improved by introducing three aluminum gallium nitrogen layers with Al components gradually decreased in a stepped manner because the atomic radii of Ga atoms and Al atoms are greatly different, and I have the advantage that the crystal quality of the GaN material is improvedWhen MOCVD is adopted to grow the aluminum gallium nitrogen layer, atoms are not arranged in an ideal model but are randomly arranged, and the content of the Al component is controlled to be reduced gradually, so that Al can be enabled to be0.25Ga0.75N layer and Al0.15Ga0.85The 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.
Although some specific embodiments of the present invention have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof. Any modification, equivalent replacement, or improvement 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. A GaN-based LED epitaxial growth method for improving the crystallization quality is characterized by comprising the following steps:
pre-Al-plating treatment is performed on a sapphire substrate, wherein,
the pre-laid Al treatment comprises the following steps: controlling the pressure of the reaction cavity at 200-280mbar, the temperature of the reaction cavity at 1000-1020 ℃, and introducing H2As a carrier gas, introducing a TMAl source to carry out pre-paving Al treatment for 50-60s, and gradually increasing the flow of the TMAl from 80sccm to 120sccm in the pre-paving Al treatment process;
growing a pressure-gradient AlN layer and growing Al on the sapphire substrate in sequence0.45Ga0.25N layer, AlN layer with gradually-changed growth temperature and Al layer0.25Ga0.75N layer, growth of constant temperature and constant pressure AlN layer and growth of Al0.15Ga0.85N layers of a plurality of N layers, wherein,
the growth pressure-graded AlN layer includes: controlling the growth temperature at 900-920 ℃, controlling the pressure of the reaction cavity at 220mbar, and introducingNH3、N2TMAl, growing a pressure gradient AlN layer with the thickness D1 of 80-100nm on the sapphire substrate, and gradually reducing the pressure of a reaction chamber from 220mba to 110mbar in the growth process;
the grown Al0.45Ga0.25The N layer includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity unchanged at 110mbar, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the pressure gradient AlN layer0.45Ga0.25An N layer, wherein the molar composition of Al is 45%;
the growth temperature graded AlN layer includes: keeping the pressure of the reaction cavity constant at 110mbar, and introducing NH into the reaction cavity3、N2And TMAl in the Al0.45Ga0.25Growing a temperature gradient AlN layer with the thickness D2 of 160-;
the grown Al0.25Ga0.75The N layer includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity unchanged at 110mbar, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the temperature-gradient AlN layer0.25Ga0.75An N layer, wherein the molar composition of Al is 25%;
the growth constant-temperature and constant-pressure AlN layer comprises: the growth temperature is increased to 900 ℃, the pressure of the reaction cavity is increased to 130mbar, NH is introduced3、N2And TMAl in the Al0.25Ga0.75Growing 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 the reaction cavity to be constant in the growth process, wherein D3 is 3D 1;
the grown Al0.15Ga0.85The N layer includes: reducing the growth temperature to 800 ℃, keeping the pressure of the reaction cavity at 130mba constant, and introducing NH3、N2TMGa and TMAl, and growing Al with the thickness of 120-140nm on the constant-temperature and constant-pressure AlN layer0.15Ga0.85An 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 cooling.
2. The method as claimed in claim 1, wherein the GaN-based LED epitaxial growth for improving the crystal quality is characterized in that the undoped GaN layer is grown by raising the temperature to 1200 ℃ and maintaining the pressure in the reaction chamber at 150-300mbar and introducing NH with a flow rate of 30000-40000sccm3200-400sccm TMGa, 100-130L/min H2In the Al0.15Ga0.85And continuously growing an undoped GaN layer of 2-4 mu m on the N layer.
3. The GaN-based LED epitaxial growth method of claim 1, wherein the Si-doped N-type GaN layer is grown by maintaining the pressure of the reaction chamber at 150-3200-300sccm TMGa, 50-90L/min H2And 20-50sccm SiH4Continuously growing a 2-4 μm Si-doped N-type GaN layer on the undoped GaN layer, wherein the doping concentration of Si is 5E +18-1E +19atoms/cm3。
4. The epitaxial growth method of GaN-based LED for improving crystal quality of claim 1, wherein the periodically grown active layer MQW is further characterized in that,
keeping the pressure of the reaction cavity at 300-320-40sccm of TMGa, 10000-2Growing an In-doped InGaN well layer with the thickness of 3 nm;
raising the temperature to 800 ℃, keeping the pressure of the reaction cavity at 300-320-100sccm of TMGa and 100-130L/min of N2Growing a 10nm GaN barrier layer;
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 of claim 1, wherein the P-type AlGaN layer is grown by raising the temperature to 900-3Mg doping concentration of 5E +18-1E +19atoms/cm3。
6. The epitaxial growth method of GaN-based LED of claim 1, wherein the growth of the Mg-doped P-type GaN layer is further carried out by raising the temperature to 930-950 ℃ and maintaining the pressure in the reaction chamber at 200-600mbar, and the 100-300nm Mg-doped P-type GaN layer is continuously grown on the P-type AlGaN layer, with the Mg doping concentration of 1E +19-1E +20atoms/cm3。
7. The GaN-based LED epitaxial growth method for improving the crystal quality as claimed in claim 1, wherein the temperature is lowered to 800 ℃ for 20-30min, and then the temperature is cooled in a furnace.
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CN109300854A (en) * 2018-10-17 2019-02-01 湘能华磊光电股份有限公司 LED epitaxial wafer growing method
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* Cited by examiner, † Cited by third party
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JP2015035535A (en) * 2013-08-09 2015-02-19 Ｄｏｗａエレクトロニクス株式会社 Group iii nitride semiconductor epitaxial substrate, and method for manufacturing the same
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