High light efficiency gaN-based white light epitaxial structure and preparation method thereof

Abstract

The application discloses a high-light-efficiency GaN-based white light epitaxial structure and a preparation method thereof. The GaN-based white light epitaxial structure comprises, from bottom to top, a CPSS substrate, an AlN layer, a buffer layer, a UGaN layer, an NGaN layer, a multi-quantum well active region layer and a PGaN layer. The buffer layer comprises a buffer 1 layer and a buffer 2 layer. The preparation method comprises the following steps: selecting a SiO2 composite substrate as the CPSS substrate, forming an epitaxial structure on the CPSS substrate by adopting a metal organic compound chemical vapor deposition method, and growing the AlN layer, the buffer 1 layer, the buffer 2 layer, the UGaN layer, the NGaN layer, the multi-quantum well active region layer and the PGaN layer on the epitaxial structure from bottom to top. The traditional buffer layer is divided into two segments, two segments of ultra-thin buffer 1 layer and buffer 2 layer are formed, the mismatch stress generated by the lattice mismatch between the GaN thin film and the substrate and the thermal stress generated by the thermal expansion coefficient are released, the lattice mismatch of the LED chip is effectively reduced, and the light extraction efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of LED chip, and particularly relates to a high-efficiency GaN-based white light epitaxial structure and a preparation method thereof. BACKGROUND

[0002] GaN-based LED semiconductor lighting technology has the characteristics of high energy efficiency, wide spectrum and intelligence, and is a revolution of lighting sources after incandescent lamps and fluorescent lamps, which provides an important way to solve the increasingly severe energy and environmental problems, and is regarded by all countries as one of the most promising strategic emerging industries. With the entry of LED into the general lighting field, there is an urgent need for GaN-based LED chips with high quality, high reliability and high light efficiency.

[0003] Epitaxy technology promotion is the key to promoting the light efficiency improvement and cost reduction of LED lighting applications, which promotes the research of high-efficiency LED epitaxy. At present, the main body of the gallium nitride-based LED epitaxial structure is: substrate, AlN layer, buffer layer, gallium nitride buffer layer, N-type GaN layer, stress release layer, MQW active region, P-type layer. When current passes through, the electrons in the N-type region and the holes in the P-type region enter the MQW active region and recombine to emit the visible light of the required waveband. However, the existing GaN-based LED still has some problems. First, due to the lattice mismatch and thermal mismatch between the substrate material and AlGaN, a large number of defects exist in the epitaxial layer, which reduces the light output rate. For example, the Chinese invention patent with the publication number CN112736171A discloses a silicon substrate GaN-based LED and a preparation method thereof. Although its cost is relatively low, its lattice mismatch degree is relatively high, which leads to a low light output rate. Secondly, the electrons and holes are separated in space, which reduces the overlap of the electron wave function and the hole wave function, and reduces the radiation recombination efficiency. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a high-efficiency GaN-based white light epitaxial structure with high light output rate and capable of effectively reducing the lattice mismatch of the LED chip and a preparation method thereof.

[0005] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0006] The high-efficiency GaN-based white light epitaxial structure comprises, from bottom to top, a CPSS substrate, an AlN layer, a buffer layer, a UGaN layer, an NGaN layer, a multi-quantum well active region layer and a PGaN layer, wherein the buffer layer comprises a buffer1 layer and a buffer2 layer.

[0007] The beneficial effect of the present application is that the traditional buffer layer is divided into two segments to form two segments of ultra-thin buffer 1 layer and buffer 2 layer, the mismatch stress generated by the lattice mismatch between the GaN thin film and the substrate and the thermal stress generated by the thermal expansion coefficient are released, the lattice mismatch of the LED chip is effectively reduced, and the light extraction efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0008] Fig. 1 The present application is a high-efficiency GaN-based white light epitaxial structure schematic diagram.

[0009] Fig. 2 The present application is a traditional epitaxial wafer structure schematic diagram of Comparative Example 1.

[0010] Fig. 3 The present application is a luminance performance test result diagram of Comparative Example 1 and Example 4. DETAILED DESCRIPTION

[0011] To explain the technical content, purposes and effects of the present application in detail, the following will be described in conjunction with the embodiments and the accompanying drawings.

[0012] Please refer to Figs. 1-3 , a high-efficiency GaN-based white light epitaxial structure, comprising a CPSS substrate, an AlN layer, a buffer layer, a UGaN layer, a NGaN layer, a multi-quantum well active region layer and a PGaN layer arranged in order from bottom to top, wherein the buffer layer comprises a buffer 1 layer and a buffer 2 layer.

[0013] A preparation method of the above-mentioned high-efficiency GaN-based white light epitaxial structure, comprising the following steps: selecting a SiO2 composite substrate as the CPSS substrate, forming an epitaxial structure on the CPSS substrate by using a metal organic compound chemical vapor deposition method, and growing an AlN layer, a buffer 1 layer, a buffer 2 layer, a UGaN layer, a NGaN layer, a multi-quantum well active region layer and a PGaN layer in order from bottom to top on the epitaxial structure.

[0014] From the above description, the beneficial effect of the present application is that the buffer layer belongs to the nucleation layer, the traditional buffer layer is divided into two segments to form two segments of ultra-thin buffer 1 layer and buffer 2 layer, the mismatch stress generated by the lattice mismatch between the GaN thin film and the substrate and the thermal stress generated by the thermal expansion coefficient are released, the serious dislocation phenomenon caused by the traditional LED bottom layer is improved, the lattice defects are reduced, the stress distribution of the epitaxial wafer and the crystalline quality of the GaN thin film are changed, so that the carrier radiation recombination probability is increased, and the light extraction efficiency is improved.

[0015] Further, the buffer1 layer is a ternary component material layer of Al-doped AlGaN, and the buffer2 layer is a ternary component material layer of In-doped InGaN.

[0016] As can be seen from the above description, the buffer1 layer is a ternary component material layer of Al-doped AlGaN, which effectively blocks defects generated in the growth process of the nucleation layer to optimize the morphology, and the buffer2 layer is a ternary component material layer of In-doped InGaN, so that the morphology of the prepared epitaxial structure is further optimized.

[0017] Further, the thickness of the buffer1 layer is 40-60 nm, and the thickness of the buffer2 layer is 10-20 nm.

[0018] As can be seen from the above description, by limiting the thickness of the buffer1 layer and the buffer2 layer, the consistency of the photoelectric performance of the epitaxial structure is improved, and the thickness of the buffer2 layer is less than that of the buffer1 layer, thereby further improving the light output rate.

[0019] Further, the growth method of the buffer1 layer is:

[0020] S1, pre-flowing TMGa and TMAl;

[0021] S2, flowing 100-120 sccm of TMGa source and 100-150 sccm of TMAl source to grow the buffer1 layer.

[0022] Further, in S1, the temperature is 700-900°C, and the time is 3-5 min.

[0023] Further, in S2, the carrier is hydrogen and ammonia, the growth pressure interval is 100-300 Torr, and the time is 15-30 s.

[0024] As can be seen from the above description, by limiting the parameters in the preparation process of the buffer1 layer, the stress generated between the release substrate and the epitaxial layer due to lattice mismatch and thermal mismatch can be effectively relieved, and at the same time, the buffer1 layer can effectively block defects generated in the growth process of the nucleation layer to optimize the morphology, thereby further improving the light output rate.

[0025] Further, the growth method of the buffer2 layer is: flowing 100-120 sccm of TMGa source and 100-120 sccm of TMin source and closing the TMAl source to grow the buffer2 layer.

[0026] As can be seen from the above description, by preparing the buffer2 layer, the morphology of the prepared epitaxial structure is further optimized, and the light output rate of the epitaxial structure is effectively improved.

[0027] Further, the temperature in the growth method of the buffer2 layer is 700-900℃.

[0028] From the above description, it can be seen that the temperature plays an important role in the growth of the buffer2 layer, and by limiting the temperature range, the morphology defects are reduced, thereby reducing the light output rate.

[0029] Please refer to Figs. 1-3 The first embodiment of the present application is:

[0030] The high-efficiency GaN-based white light epitaxial structure comprises, from bottom to top, a CPSS substrate, an AlN layer, a buffer layer, a UGaN layer, an NGaN layer, a multi-quantum well active region layer and a PGaN layer, wherein the buffer layer comprises a buffer1 layer with a thickness of 40nm and a buffer2 layer with a thickness of 10nm, the buffer1 layer is a ternary component material layer of Al-doped AlGaN, and the buffer2 layer is a ternary component material layer of In-doped InGaN.

[0031] Please refer to Figs. 1-3 The second embodiment of the present application is:

[0032] The difference between the second embodiment and the first embodiment is only that the thickness of the buffer1 layer is 60nm and the thickness of the buffer2 layer is 20nm.

[0033] Please refer to Figs. 1-3 The third embodiment of the present application is:

[0034] The difference between the third embodiment and the first embodiment is only that the thickness of the buffer1 layer is 50nm and the thickness of the buffer2 layer is 15nm.

[0035] Please refer to Figs. 1-3 The fourth embodiment of the present application is:

[0036] The preparation method of the high-efficiency GaN-based white light epitaxial structure comprises the following steps:

[0037] (1) The CPSS substrate is a composite substrate of sapphire and SiO2, and the substrate is placed in the reaction cavity of a metal organic chemical vapor deposition device, the pressure of the reaction cavity is 500mbar, the temperature is 1000℃, hydrogen gas is used as the carrier gas for substrate surface treatment, the process duration is 5min, and the AlN layer is grown;

[0038] (2) Temperature is adjusted to 700℃, and after 3min of pre-flow of TMGa and TMAl, Buffer 1 layer with a thickness of 40nm is grown with hydrogen and ammonia as carriers, 100sccm of TMGa source and 100sccm of TMAl are inputted, and the growth pressure interval is 100Torr. The process duration is 15s.

[0039] (3) The temperature and pressure are kept unchanged, Buffer 2 layer with a thickness of 10nm is grown with hydrogen and ammonia as carriers, 100sccm of TMGa source and 100sccm of TMin source are inputted, and the TMAl source is closed. The process duration is 30s.

[0040] (4) The temperature is increased to 1000℃, the reaction chamber pressure is increased to 250mbar, and UGaN layer is formed by inputting 300sccm of TMGa2 source for 6min.

[0041] (5) The reaction chamber pressure is increased to 500mbar, and NGaN layer with a thickness of 2μm is grown.

[0042] (6) The temperature is decreased to 700℃, 1200sccm of TMIn source and 25sccm of TMGa source are inputted, and InGaN / GaN multi-quantum well active region layer with a thickness of 0.15μm is periodically grown. The period number is 10, and the In doping concentration is 1E+20atom / cm 3 ;

[0043] (7) In the reaction chamber with a temperature of 600℃ and a pressure of 300mbar, 55000sccm of NH3, 25sccm of TMGa source are inputted, and low-temperature PGaN layer with a thickness of 60nm is formed.

[0044] (8) The temperature is increased to 700℃, 30000sccm of NH3, 30sccm of TMGa, 1500sccm of Cp2Mg source and 150sccm of TMAl source are inputted, and high-temperature normally doped AlGaN / GaN superlattice layer is grown. The Mg doping concentration is 1E+18atom / cm 3 , the Al doping concentration is 1E+17atom / cm 3 , the single layer thickness of AlGaN or GaN is 4nm, the thickness ratio of AlGaN and GaN layers in a single period is 1:1, the period is 5, and the total thickness is 50nm.

[0045] (9) Finally, the temperature is raised to 900℃, the pressure in the reaction chamber is 600mbar, 60000sccm of NH3, 25sccm of TMGa source and 2000sccm of Cp2 (dimethyl magnesium) Mg source are introduced to form a high-temperature and high-doping PGaN layer with a thickness of 60nm, wherein the doping concentration of Mg is 1E+20 atom / cm 3 ;

[0046] (10) After the epitaxial structure growth is completed, the temperature of the reaction chamber is reduced, and annealing treatment is performed in a nitrogen atmosphere, the annealing temperature range is 650℃, the time length is 5min, and the epitaxial growth is completed after cooling to room temperature.

[0047] Please refer to Figs. 1-3 Embodiment five of the present application is:

[0048] The preparation method of the high-efficiency GaN-based white light epitaxial structure comprises the following steps:

[0049] (1) The CPSS substrate adopts a sapphire and SiO2 composite substrate, the substrate is placed in a reaction chamber of a metal organic chemical vapor deposition device, the pressure of the reaction chamber is 600mbar, the temperature is 1200℃, hydrogen is used as a carrier gas to perform substrate surface treatment, the process duration is 8min, and an AlN layer is grown.

[0050] (2) The temperature is adjusted to 900℃, 5min of TMGa and TMAl pre-flow is performed, hydrogen and ammonia are used as carriers, 120sccm of TMGa source and 150sccm of TMAl are introduced, a Buffer1 layer with a thickness of 60nm is grown, the growth pressure range is 300Torr, and the process duration is 30s.

[0051] (3) The temperature and pressure are kept unchanged, hydrogen and ammonia are used as carriers, 120sccm of TMGa source and 120sccm of TMin source are introduced, the TMAl source is closed, a Buffer2 layer with a thickness of 20nm is grown, and the process duration is 40s.

[0052] (4) The temperature is raised to 1100℃, the pressure in the reaction chamber is raised to 350mbar, 400sccm of TMGa2 source is introduced, the process lasts for 9min, and a UGaN layer is formed.

[0053] (5) The pressure in the reaction chamber is increased to 1000mbar, and a NGaN layer with a thickness of 3μm is grown.

[0054] (6) cooling to 800℃, 1500sccm of TMIn source and 40sccm of TMGa source are inputted, and InGaN / GaN multi-quantum well active region layer is periodically grown, the thickness is 0.2μm, the period number is 10-16, and the In doping concentration is 2E+20atom / cm 3 ;

[0055] (7) in the reaction chamber with temperature 700℃ and pressure 800mbar, 65000sccm of NH3, 50sccm of TMGa source are inputted, and low-temperature PGaN layer is formed, the thickness is 90nm.

[0056] (8) heating to 950℃, 60000sccm of NH3, 50sccm of TMGa, 2000sccm of Cp2Mg source and 200sccm of TMAl source are inputted, and high-temperature normal-doped AlGaN / GaN superlattice layer is grown, wherein the Mg doping concentration is 1E+19atom / cm 3 , the Al doping concentration is 1E+18atom / cm 3 , the single-layer thickness of AlGaN or GaN is 6nm, the thickness ratio of AlGaN and GaN layer in a single period is 3:1, the period is 10, and the total thickness is 70nm.

[0057] (9) finally, the temperature is increased to 1050℃, the pressure of the reaction chamber is 1000mbar, 75000sccm of NH3, 50sccm of TMGa source and 3000sccm of Cp2(dicyclopentadienyl) Mg source are inputted, and high-temperature high-doped PGaN layer is formed, the thickness is 90nm, and the Mg doping concentration is 1E+20atom / cm 3 ;

[0058] (10) after the epitaxial structure growth is completed, the reaction cavity temperature is reduced, and annealing treatment is carried out in a nitrogen atmosphere, the annealing temperature range is 850℃, the time length is 15min, and the cooling to room temperature is completed.

[0059] Please refer to Figs. 1-3 , the embodiment six of the present application is:

[0060] The preparation method of the high-light-efficiency GaN-based white light epitaxial structure comprises the following steps:

[0061] (1) the CPSS substrate adopts sapphire and SiO2 composite substrate, the substrate is placed into the reaction cavity of a metal organic chemical vapor deposition device, the pressure of the reaction cavity is 550mbar, the temperature is 1100℃, hydrogen is used as a carrier gas to treat the surface of the substrate, the process duration is 6min, and AlN layer is grown;

[0062] (2) Temperature is adjusted to 800℃, and after 4min of pre-flow of TMGa and TMAl, Buffer 1 layer with a thickness of 50nm is grown with hydrogen and ammonia as carriers, 110sccm of TMGa source and 130sccm of TMAl, and the growth pressure is in the range of 200Torr, and the process duration is 20s.

[0063] (3) The temperature and pressure are kept unchanged, Buffer 2 layer with a thickness of 15nm is grown with hydrogen and ammonia as carriers, 110sccm of TMGa source and 110sccm of TMin source, and the TMAl source is turned off, and the process duration is 40min.

[0064] (4) The temperature is increased to 1050℃, the reaction chamber pressure is increased to 300mbar, and UGaN layer is formed by introducing 350sccm of TMGa2 source for 8min.

[0065] (5) The reaction chamber pressure is increased to 800mbar, and NGaN layer with a thickness of 2.5μm is grown.

[0066] (6) The temperature is decreased to 750℃, and InGaN / GaN multi-quantum well active region layer with a thickness of 0.17μm, a period number of 13, and In doping concentration of 2E+20atom / cm 3 ;

[0067] (7) At the temperature of 650℃ and the pressure of 500mbar in the reaction chamber, low-temperature PGaN layer with a thickness of 70nm is formed by introducing 60000sccm of NH3 and 40sccm of TMGa source.

[0068] (8) The temperature is increased to 800℃, and high-temperature normally doped AlGaN / GaN superlattice layer is grown by introducing 50000sccm of NH3, 40sccm of TMGa, 1800sccm of Cp2Mg source and 180sccm of TMAl source; wherein the Mg doping concentration is 1E+19atom / cm 3 , the Al doping concentration is 1E+18atom / cm 3 , the single layer thickness of AlGaN or GaN is 5nm, the thickness ratio of AlGaN and GaN layers in a single period is 2:1, the period is 8, and the total thickness is 60nm.

[0069] (9) Finally, the temperature is raised to 1000℃, the pressure in the reaction chamber is 800mbar, 70000sccm of NH3, 40sccm of TMGa source and 2500sccm of Cp2 (dimethyl magnesium) Mg source are introduced to form a high-temperature and high-doped PGaN layer with a thickness of 70nm, wherein the doping concentration of Mg is 1E+20 atom / cm 3 ;

[0070] (10) After the growth of the epitaxial structure is completed, the temperature of the reaction chamber is reduced, and annealing treatment is performed in a nitrogen atmosphere, the annealing temperature range is 800℃, the time length is 10 minutes, and the cooling is completed at room temperature.

[0071] Comparative Example One

[0072] The difference between Comparative Example One and Example Four is only that a single buffer layer is used;

[0073] Specifically, steps (2) and (3) are replaced by the following methods:

[0074] The pressure in the reaction chamber is reduced to 100mbar, the temperature is 800℃, hydrogen and ammonia are used as carriers, 60sccm of TMGa2 source and 25sccm of TMAl source are introduced at the same time, a buffer layer with a thickness of 0.1μm is grown on the substrate, and the process lasts for 4-6 minutes.

[0075] Test Example One

[0076] The brightness performance of Example Four and Comparative Example One is detected, and the data are as shown in Fig. 3 , wherein the lighter gray represents the data of Comparative Example One, the darker gray represents the data of Example Four, the horizontal coordinate is the current, the unit is ma, and the vertical coordinate is the brightness, the unit is mw.

[0077] Comparative Example One is a traditional epitaxial structure, and Example Four is a high-brightness epitaxial structure according to the present application. Fig. 3 It can be seen that the brightness of the high-brightness epitaxial structure prepared by Example Four is obviously improved compared with the traditional epitaxial structure prepared by Comparative Example One.

[0078] In summary, the high light efficiency GaN-based white light epitaxial structure and the preparation method thereof provided by the application use a new type of buffer layer to replace the traditional buffer layer, that is, the traditional buffer layer is divided into two sections to form two sections of ultra-thin buffer 1 layer and buffer 2 layer, the mismatch stress generated between the GaN thin film and the substrate due to the lattice mismatch and the thermal stress generated due to the thermal expansion coefficient are released, the dislocation serious phenomenon caused by the traditional LED bottom layer is improved, the lattice mismatch of the LED chip is effectively reduced, the lattice defects are reduced, the stress distribution of the epitaxial wafer is changed, and the crystalline quality of the GaN thin film is changed, so that the carrier radiation recombination probability is increased, and the light extraction efficiency is improved.

[0079] The above description is only an embodiment of the application, and does not limit the patent scope of the application, and any equivalent transformation or direct or indirect application in the related technical field by using the content of the specification and drawings is also included in the patent protection scope of the application.

Claims

1. A high efficiency GaN-based white light epitaxial structure, characterized in that, The CPSS substrate, the AlN layer, the buffer layer, the UGaN layer, the NGaN layer, the multi-quantum well active region layer and the PGaN layer are sequentially arranged from bottom to top, wherein the buffer layer comprises a buffer1 layer and a buffer2 layer. The buffer1 layer is a ternary component material layer of Al-doped AlGaN, and the buffer2 layer is a ternary component material layer of In-doped InGaN. 2.The high light efficiency GaN-based white light epitaxial structure of claim 1, wherein, The thickness of the buffer1 layer is 40-60 nm, and the thickness of the buffer2 layer is 10-20 nm.

3. The method for preparing high light efficiency GaN-based white light epitaxial structure according to claim 1, characterized in that, The method comprises the following steps: The SiO2 composite substrate is selected as the CPSS substrate, an epitaxial structure is formed on the CPSS substrate by using a metal organic chemical vapor deposition method, and the AlN layer, the buffer1 layer, the buffer2 layer, the UGaN layer, the NGaN layer, the multi-quantum well active region layer and the PGaN layer are sequentially grown on the epitaxial structure from bottom to top.

4. The method of claim 3, wherein the method further comprises: The growth method of the buffer1 layer is as follows: S1, TMGa and TMAl are pre-flowed; S2, the buffer1 layer is grown by introducing 100-120 sccm of TMGa source and 100-150 sccm of TMAl source.

5. The method of claim 4, wherein the method further comprises: In S1, the temperature is 700-900 DEG C, and the time is 3-5 min.

6. The method of claim 4, wherein the method further comprises: In S2, the carrier is hydrogen and ammonia, the growth pressure interval is 100-300 Torr, and the time is 15-30 s.

7. The method for preparing a high-efficiency GaN-based white-light epitaxial structure according to claim 3, characterized in that, The growth method of the buffer2 layer is as follows: the buffer2 layer is grown by introducing 100-120 sccm of TMGa source and 100-120 sccm of TMin source and closing the TMAl source.

8. The method of claim 7, wherein the method further comprises: In the growth method of the buffer2 layer, the temperature is 700-900 DEG C.

9. The method of claim 7, wherein the method further comprises: In the growth method of the buffer2 layer, the carrier is hydrogen and ammonia, the growth pressure interval is 100-300 Torr, and the time is 30-40 s.

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