An epitaxial structure for improving micro LED modulation bandwidth and preparation method thereof

Abstract

The present application relates to an epitaxial structure for improving the modulation bandwidth of a micro-LED and a preparation method thereof, and relates to the field of semiconductor optoelectronic devices, which includes an epitaxial substrate, on which a GaN buffer layer, an n-type GaN layer, an InGaN / GaN multi-quantum well active region, a p-type AlGaN electron blocking layer and a p-type GaN layer are sequentially grown, the InGaN / GaN multi-quantum well active region includes staggered stacked GaN quantum barrier layers and InGaN quantum well layers, a first two-dimensional material layer is arranged between the InGaN / GaN multi-quantum well active region and the n-type GaN layer, a second two-dimensional material layer is interspersed between adjacent GaN quantum barrier layers and InGaN quantum well layers, and a third two-dimensional material layer is arranged between the InGaN / GaN multi-quantum well active region and the p-type AlGaN electron blocking layer. The present application has the effect of blocking the growth of threading dislocations and reducing the lattice mismatch between the quantum barrier layer and the quantum well layer, thereby weakening the polarization electric field of the micro-LED device, and increasing the spatial overlap rate of electron holes, thereby improving the modulation bandwidth and luminous efficiency of the micro-LED device.

Description

Technical Field

[0001] The present application relates to the field of semiconductor optoelectronic devices, and in particular to an epitaxial structure for improving the modulation bandwidth of a micro-LED and a preparation method thereof. Background Art

[0002] Visible light communication technology refers to the technology that uses light in the visible light band as an information carrier to achieve information transmission in free space. It has the advantages of rich spectrum, safety and reliability, green environmental protection and high confidentiality.

[0003] In the related art, a Chinese patent with announcement number CN111816742A discloses a GaN-based LED epitaxial structure for visible light communication and a preparation method thereof, comprising a substrate; a buffer layer located on the substrate; an n-type GaN layer located on the buffer layer; an n-type AlGaN electron blocking layer located on the n-type GaN layer; an InGaN / GaN multi-quantum well active region located on the n-type AlGaN electron blocking layer; and a p-type GaN layer located on the InGaN / GaN multi-quantum well active region. The LED epitaxial structure provided by the present invention reduces the hindering effect of the electron blocking layer on the hole injection quantum well, thereby improving the hole injection efficiency; and the LED epitaxial structure can also improve the radiation recombination coefficient, thereby simultaneously improving the maximum optical power and the maximum modulation bandwidth.

[0004] Regarding the above-mentioned related technologies, the inventors believe that by using a new epitaxial structure, the obstruction of the p-type electron blocking layer to hole injection is eliminated, but this also aggravates the leakage of electrons from the n-type GaN side to the p-type GaN side, reducing the luminous efficiency of the device, and there is still room for improvement. Summary of the invention

[0005] In order to improve the problem that the use of a new epitaxial structure exacerbates the leakage of electrons from the n-type GaN side to the p-type GaN side, thereby reducing the luminous efficiency of the device, the present application provides an epitaxial structure for improving the modulation bandwidth of a micro LED and a preparation method thereof.

[0006] In the first aspect, the present application provides an epitaxial structure for improving the modulation bandwidth of a micro-LED using the following technical solution:

[0007] An epitaxial structure for improving the modulation bandwidth of a micro LED comprises an epitaxial substrate, on which a GaN buffer layer, an n-type GaN layer, an InGaN / GaN multi-quantum well active region, a p-type AlGaN electron blocking layer and a p-type GaN layer are sequentially grown, the InGaN / GaN multi-quantum well active region comprises staggered stacked GaN quantum barrier layers and InGaN quantum well layers, a first two-dimensional material layer is arranged between the InGaN / GaN multi-quantum well active region and the n-type GaN layer, a second two-dimensional material layer is interspersed between adjacent GaN quantum barrier layers and InGaN quantum well layers, and a third two-dimensional material layer is arranged between the InGaN / GaN multi-quantum well active region and the p-type AlGaN electron blocking layer.

[0008] By adopting the above technical solution, due to the presence of the two-dimensional material layer, blocking the growth of threading dislocations can also reduce the lattice mismatch between the quantum barrier layer and the quantum well layer, thereby weakening the polarization electric field of the micro LED device and increasing the spatial overlap rate of electrons and holes, thereby improving the modulation bandwidth and luminous efficiency of the micro LED device; on the other hand, the two-dimensional material is easy to mechanically peel off, which can also greatly reduce production costs.

[0009] Optionally, a fourth two-dimensional material layer is arranged between the epitaxial substrate and the GaN buffer layer.

[0010] By adopting the above technical solution, a two-dimensional material layer is first grown on the epitaxial substrate, and then a GaN buffer layer is grown, so that the compressive stress in the GaN thin film layer can be released, thereby improving the modulation bandwidth and luminous efficiency of the micro LED device.

[0011] Optionally, a two-dimensional material film is provided between the first two-dimensional material layer and the n-type GaN layer, and patterned holes are provided on the two-dimensional material film and the n-type GaN layer.

[0012] By adopting the above technical solution, holes are opened in the two-dimensional material film and the n-type GaN layer, so that the first two-dimensional material layer can be selectively epitaxially grown. The prepared micro LED device can avoid the influence of side wall defects caused by dry etching, thereby improving the luminous efficiency.

[0013] Optionally, the two-dimensional material film can be replaced by a SiO2 film.

[0014] By adopting the above technical solution and setting a SiO2 film, it is convenient to open holes in this material, so that the first two-dimensional material layer can be selectively epitaxially grown. The prepared micro LED device can avoid the influence of side wall defects caused by dry etching, thereby improving the luminous efficiency.

[0015] In a second aspect, the present application provides a method for preparing the above-mentioned epitaxial structure, which adopts the following technical solution:

[0016] A preparation method comprising:

[0017] Step S1, depositing and growing a fourth two-dimensional material layer, a GaN buffer layer, and an n-type GaN layer in sequence on an epitaxial substrate;

[0018] Step S2, depositing a two-dimensional material film or a SiO2 film on the n-type GaN layer;

[0019] Step S3, patterning and opening holes in the two-dimensional material film or the SiO2 film, and extending the holes to the n-type GaN layer;

[0020] Step S4, growing a first two-dimensional material layer on the two-dimensional material film or SiO2 film after the holes are opened;

[0021] Step S5, growing a GaN quantum barrier layer on the first two-dimensional material layer;

[0022] Step S6, growing a second two-dimensional material layer on the GaN quantum barrier layer;

[0023] Step S7, growing an InGaN quantum well layer on the second two-dimensional material layer;

[0024] Step S8, growing a first two-dimensional material layer on the InGaN quantum well layer;

[0025] Step S9, growing a third two-dimensional material layer on the InGaN / GaN multi-quantum well active region;

[0026] Step S10, sequentially growing a p-type AlGaN electron blocking layer and a p-type GaN layer on the third two-dimensional material layer;

[0027] Step S11, performing photolithography, etching and deposition processes on the formed epitaxial structure to prepare a metal electrode.

[0028] By adopting the above technical solution, on the one hand, by introducing a two-dimensional material layer to epitaxially grow a GaN film, since the lattice mismatch between the two-dimensional material layer and GaN is only 0.86%, the compressive stress in the GaN film can be released, reducing the dislocations and electric fields caused by the lattice mismatch. In addition, by adopting a new quantum well structure, inserting the two-dimensional material layer between the quantum barrier layer and the InGaN quantum well layer can not only further block the extension of the penetration dislocation and improve the luminous efficiency, but also further reduce the lattice mismatch between GaN and InGaN, thereby weakening the polarization electric field in the micro-LED device. On the other hand, through the selective epitaxial growth method, the prepared micro-LED device can completely avoid the influence of sidewall defects caused by dry etching, thereby improving the luminous efficiency. While increasing the modulation bandwidth of the micro-LED device, it can still maintain the good luminous efficiency of the micro-LED device, thereby meeting the high bandwidth and long distance requirements of the visible light communication system, and because the two-dimensional material is easy to mechanically peel off, it can also greatly reduce the production cost.

[0029] Optionally, before step S9, steps S5 to S8 are repeated to complete the growth of the InGaN / GaN multi-quantum well active region.

[0030] By adopting the above technical solution and repeating the steps, due to the presence of the two-dimensional material, the luminescence efficiency of the quantum well active area is greatly improved. Blocking the growth of penetrating dislocations can also reduce the lattice mismatch between the quantum barrier layer and the quantum well layer, thereby weakening the polarization electric field of the micro LED device and increasing the spatial overlap rate of electrons and holes.

[0031] Optionally, after the fourth two-dimensional material layer is grown, an unintentionally doped GaN buffer layer is grown at 1205° C. using MOCVD equipment, wherein the thickness of the GaN buffer layer is between 2 μm and 5 μm.

[0032] Optionally, in step S3, the porous two-dimensional material is patterned by photolithography and etching processes, wherein the size of the holes is at the micron level and the spacing between the holes is also at the micron level.

[0033] Optionally, in step S7, when growing the quantum well layer, the InGaN quantum well layer contains full-band light emission from blue light to red light.

[0034] Optionally, in step S10, a p-type AlGaN electron blocking layer is grown on the InGaN / GaN multi-quantum well active region layer at a temperature in the range of 830° C., wherein the thickness of the p-type AlGaN electron blocking layer is between 20 nm and 30 nm;

[0035] A p-type GaN layer is grown on the p-type AlGaN electron blocking layer at a temperature within a range of 1140° C., wherein the thickness of the p-type GaN layer is between 150 nm and 200 nm.

[0036] In summary, the present application includes at least one of the following beneficial technical effects:

[0037] 1. Due to the presence of the two-dimensional material layer, blocking the growth of threading dislocations can also reduce the lattice mismatch between the quantum barrier layer and the quantum well layer, thereby weakening the polarization electric field of the micro-LED device and increasing the spatial overlap rate of electrons and holes, thereby improving the modulation bandwidth and luminous efficiency of the micro-LED device;

[0038] 2. Two-dimensional materials are easy to mechanically peel off, which can also greatly reduce production costs;

[0039] 3. By opening holes in the two-dimensional material film and the n-type GaN layer, the first two-dimensional material layer can be selectively epitaxially grown, and the prepared micro LED device can avoid the influence of side wall defects caused by dry etching, thereby improving the luminous efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural schematic diagram of an epitaxial structure for improving the modulation bandwidth of a micro-LED in an embodiment of the present application.

[0041] Explanation of the accompanying drawings: 1. epitaxial substrate; 2. fourth two-dimensional material layer; 3. GaN buffer layer; 4. n-type GaN layer; 5. two-dimensional material film; 6. patterned holes; 7. first two-dimensional material layer; 8. InGaN / GaN multi-quantum well active region; 9. GaN quantum barrier layer; 10. InGaN quantum well layer; 11. second two-dimensional material layer; 12. third two-dimensional material layer; 13. p-type AlGaN electron blocking layer; 14. p-type GaN layer. DETAILED DESCRIPTION

[0042] The following is combined with Figure 1 This application is described in further detail.

[0043] The present application embodiment discloses an epitaxial structure for improving the modulation bandwidth of a micro LED. Figure 1 The epitaxial structure for improving the modulation bandwidth of the micro LED includes an epitaxial substrate 1, a fourth two-dimensional material layer 2, a GaN buffer layer 3, an n-type GaN layer 4, a two-dimensional material film 5, a first two-dimensional material layer 7, an InGaN / GaN multi-quantum well active region 8, a third two-dimensional material layer 12, a p-type AlGaN electron blocking layer 13 and a p-type GaN layer 14.

[0044] The epitaxial substrate 1 is not limited to a sapphire substrate, but may also be a silicon, silicon carbide, or gallium nitride substrate, with a size of, for example, 2, 4, 6, or 8 inches, so that the size of the substrate can be reduced and is suitable for micro LED devices.

[0045] The fourth two-dimensional material layer 2 grows on the epitaxial substrate 1, and the growth method can be a deposition method. In addition, the material of the fourth two-dimensional material layer 2 can be any one of graphene, MoS2, WSe2, h-BN, MoTe2, ReS2, etc., or it can be a combination of two or more.

[0046] The GaN buffer layer 3 is grown on the fourth two-dimensional material layer 2. In the present embodiment, the GaN buffer layer 3 is an unintentionally doped GaN buffer layer 3 with a thickness between 2 μm and 5 μm. Since the lattice mismatch between the two-dimensional material and the GaN buffer layer 3 is only 0.86%, the compressive stress in the GaN buffer layer 3 can be released, thereby reducing the dislocations and electric fields caused by the lattice mismatch.

[0047] The n-type GaN layer 4 grows on the GaN buffer layer 3. After the growth of the n-type GaN layer 4 is completed, the two-dimensional material film 5 begins to be deposited on the n-type GaN layer 4. The material of the two-dimensional material film 5 here can be the same as the material of the fourth two-dimensional material layer 2. In this embodiment, the two-dimensional material film 5 can be replaced by a SiO2 film, which can also achieve the same purpose.

[0048] The two-dimensional material film 5 has patterned holes 6, which extend to the n-type GaN layer 4 during the hole opening process, thereby avoiding damage caused by dry etching and allowing the material to be grown subsequently to be selectively grown.

[0049] The first two-dimensional material layer 7 grows on the two-dimensional material film 5 after the hole is opened. The material of the first two-dimensional material layer 7 here can be the same as the material of the fourth two-dimensional material layer 2, but the material of the first two-dimensional material layer 7 here is a p-type doped two-dimensional material layer with a thickness of several nm, which is easy to mechanically peel off, greatly reducing the production cost.

[0050] The InGaN / GaN multi-quantum well active region 8 is grown on the first two-dimensional material layer 7. The InGaN / GaN multi-quantum well active region 8 includes a number of GaN quantum barrier layers 9 and a number of InGaN quantum well layers 10. A number of GaN quantum barrier layers 9 and a number of InGaN quantum well layers 10 are stacked on each other, and the InGaN quantum well layer 10 contains a full band from blue light to red light, and can emit full-band light. A second two-dimensional material layer 11 is interspersed between adjacent GaN quantum barrier layers 9 and InGaN quantum well layers 10. The material of the second two-dimensional material layer 11 can be the same as that of the fourth two-dimensional material layer 2. Further blocking the growth of penetrating dislocations can also reduce the lattice mismatch between the GaN quantum barrier layer 9 and the InGaN quantum well layer 10, thereby weakening the polarization electric field of the micro-LED device and increasing the spatial overlap rate of electron holes, thereby improving the modulation bandwidth and luminous efficiency of the micro-LED device. Among them, the layer closest to the first two-dimensional material layer 7 is the GaN quantum barrier layer 9.

[0051] The third two-dimensional material layer 12 is grown on the InGaN / GaN multi-quantum well active region 8, and can also be a p-type doped two-dimensional material, which is easy to mechanically peel off, greatly reducing the production cost. Among them, in the InGaN / GaN multi-quantum well active region 8, the InGaN quantum well layer 10 is closest to the third two-dimensional material layer 12.

[0052] The p-type AlGaN electron blocking layer 13 is grown on the third two-dimensional material layer 12 , and has a thickness of about 20 nm to 30 nm. The p-type GaN layer 14 is grown on the p-type AlGaN electron blocking layer 13 , and has a thickness of about 150 nm to 200 nm.

[0053] The implementation principle of an epitaxial structure for improving the modulation bandwidth of a micro-LED in the embodiment of the present application is as follows: on the one hand, by introducing a two-dimensional material to epitaxially grow a GaN buffer layer 3, since the lattice mismatch between the two-dimensional material and GaN is only 0.86%, the compressive stress in the GaN buffer layer 3 can be released, reducing the dislocation and electric field caused by the lattice mismatch. In addition, by adopting a new quantum well structure, inserting the two-dimensional material between the GaN quantum barrier layer 9 and the InGaN quantum well layer 10 can not only further block the extension of the penetration dislocation and improve the luminous efficiency, but also further reduce the lattice mismatch between GaN and InGaN, thereby achieving the weakening of the polarization electric field in the micro-LED device. On the other hand, through the selective epitaxial growth method, the prepared micro-LED device can completely avoid the influence of the sidewall defects caused by dry etching, thereby improving the luminous efficiency, and while improving the modulation bandwidth of the micro-LED device, it can still maintain the good luminous efficiency of the micro-LED device, thereby meeting the high bandwidth and long distance requirements of the visible light communication system, and because the two-dimensional material is easy to mechanically peel off, it can also greatly reduce the production cost.

[0054] The embodiment of the present application also discloses a method for preparing an epitaxial structure.

[0055] A preparation method comprises:

[0056] Step S1 , depositing and growing a fourth two-dimensional material layer 2 , a GaN buffer layer 3 , and an n-type GaN layer 4 in sequence on an epitaxial substrate 1 .

[0057] The substrate material may be a 2-inch c-plane sapphire substrate, or other materials and other sizes. The fourth two-dimensional material layer 2 may be a graphene layer with a thickness of several nm. On the graphene layer, an unintentionally doped GaN buffer layer 3 is grown at 1205°C using MOCVD equipment, and the thickness of the GaN buffer layer 3 is between 2 μm and 5 μm.

[0058] Step S2, depositing a two-dimensional material film 5 or a SiO 2 film on the n-type GaN layer 4.

[0059] The two-dimensional material film 5 or SiO2 film needs to have a certain thickness to facilitate operations such as opening holes in the layer later.

[0060] Step S3 , patterning the two-dimensional material film 5 or the SiO 2 film to form holes, and extending the holes to the n-type GaN layer 4 .

[0061] The holes are opened by photolithography and etching processes. The size of the holes is at the micron level, and the hole spacing is also at the micron level, so as to reduce the damage to the LED side wall during the dry etching process, effectively improve the luminous efficiency, and facilitate the subsequent selection and growth of other materials.

[0062] Step S4, growing a first two-dimensional material layer 7 on the two-dimensional material film 5 or the SiO2 film after the holes are opened.

[0063] Here, the first two-dimensional material layer 7 can be a p-type doped graphene layer, or any p-type doped two-dimensional material, such as MoS2, WSe2, h-BN, MoTe2, ReS2, etc.

[0064] Step S5 , growing a GaN quantum barrier layer 9 on the first two-dimensional material layer 7 .

[0065] The thickness of the GaN quantum barrier layer 9 grown here is about 3 nm to 5 nm.

[0066] Step S6 , growing a second two-dimensional material layer 11 on the GaN quantum barrier layer 9 .

[0067] The second two-dimensional material layer 11 may also be a p-type doped graphene layer like the first two-dimensional material layer 7 .

[0068] Step S7 , growing an InGaN quantum well layer 10 on the second two-dimensional material layer 11 .

[0069] The InGaN quantum well layer 10 can include a wavelength band from blue light to green light, and emit light of the full wavelength band.

[0070] Step S8 , growing a first two-dimensional material layer 7 on the InGaN quantum well layer 10 .

[0071] The growth process here is to correspond to step S5. After step S8, steps S5-S8 are repeated so that two-dimensional materials are interspersed between adjacent GaN quantum barrier layers 9 and InGaN quantum well layers 10, and two-dimensional materials also exist between the two-dimensional material film 5 and the subsequent layers, and finally form an InGaN / GaN multi-quantum well active region 8. In this process, taking 5 repetitions as an example, 6 cycles of InGaN quantum well layers 10 are formed, which improves the luminous efficiency and greatly reduces the production cost because the two-dimensional material is easy to mechanically peel off.

[0072] Step S9 , growing a third two-dimensional material layer 12 on the InGaN / GaN multi-quantum well active region 8 .

[0073] The third two-dimensional material layer 12 is consistent with the first two-dimensional material layer 7 and the second two-dimensional material layer 11 , and is a p-type doped graphene layer.

[0074] Step S10 , sequentially growing a p-type AlGaN electron blocking layer 13 and a p-type GaN layer 14 on the third two-dimensional material layer 12 .

[0075] The p-type AlGaN electron blocking layer 13 is grown at a temperature of 830°C, and the thickness of the p-type AlGaN electron blocking layer 13 is between 20nm and 30nm. The p-type GaN layer 14 is grown at a temperature of 1140°C, and the thickness of the p-type GaN layer 14 is between 150nm and 200nm.

[0076] Step S11, performing photolithography, etching and deposition processes on the formed epitaxial structure to prepare a metal electrode.

[0077] Prior to this, the epitaxially grown epitaxial wafer needs to be cleaned.

[0078] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. An epitaxial structure for improving the modulation bandwidth of a micro LED, comprising an epitaxial substrate (1), on which a GaN buffer layer (3), an n-type GaN layer (4), an InGaN / GaN multi-quantum well active region (8), a p-type AlGaN electron blocking layer (13) and a p-type GaN layer (14) are sequentially grown, characterized in that: The InGaN / GaN multi-quantum well active region (8) comprises GaN quantum barrier layers (9) and InGaN quantum well layers (10) that are stacked in an alternating manner; a two-dimensional material layer is provided between the InGaN / GaN multi-quantum well active region (8) and the n-type GaN layer (4); two-dimensional material layers are interspersed between adjacent GaN quantum barrier layers (9) and InGaN quantum well layers (10); a two-dimensional material layer is provided between the InGaN / GaN multi-quantum well active region (8) and the p-type AlGaN electron blocking layer (13); another two-dimensional material layer is provided between the epitaxial substrate (1) and the GaN buffer layer (3); a two-dimensional material film (5) is provided between the another two-dimensional material layer and the n-type GaN layer (4); and patterned holes (6) are provided on the two-dimensional material film (5) and the n-type GaN layer (4).

2. The epitaxial structure for improving the modulation bandwidth of a micro-LED according to claim 1, characterized in that: The two-dimensional material film (5) is replaced by a SiO2 film.

3. A method for preparing an epitaxial structure according to claim 1 or 2, characterized in that: include: Step S1, depositing and growing a two-dimensional material layer, a GaN buffer layer (3), and an n-type GaN layer (4) in sequence on an epitaxial substrate (1); Step S2, depositing a two-dimensional material film (5) or a SiO2 film on the n-type GaN layer (4); Step S3, patterning the two-dimensional material film (5) or the SiO2 film to form holes, and extending the holes to the n-type GaN layer (4); Step S4, growing a two-dimensional material layer on the two-dimensional material film (5) or the SiO2 film after the holes are opened; Step S5, growing a GaN quantum barrier layer (9) on the two-dimensional material layer; Step S6, growing a two-dimensional material layer on the GaN quantum barrier layer (9); Step S7, growing an InGaN quantum well layer (10) on the two-dimensional material layer; Step S8, growing a two-dimensional material layer on the InGaN quantum well layer (10); Step S9, growing a two-dimensional material layer on the InGaN / GaN multi-quantum well active region (8); Step S10, sequentially growing a p-type AlGaN electron blocking layer (13) and a p-type GaN layer (14) on the two-dimensional material layer; Step S11, performing photolithography, etching and deposition processes on the formed epitaxial structure to prepare a metal electrode.

4. The preparation method according to claim 3, characterized in that: Before step S9, steps S5 to S8 are repeated to complete the growth of the InGaN / GaN multi-quantum well active region (8).

5. The preparation method according to claim 3, characterized in that: In step S1, after the two-dimensional material layer is grown, an unintentionally doped GaN buffer layer (3) is grown at 1205° C. using MOCVD equipment, wherein the thickness of the GaN buffer layer (3) is between 2 μm and 5 μm.

6. The preparation method according to claim 3, characterized in that: In step S3, the porous two-dimensional material is patterned by photolithography and etching processes, wherein the size of the holes is in the micron level and the spacing between the holes is also in the micron level.

7. The preparation method according to claim 3, characterized in that: In step S7, when the InGaN quantum well layer (10) is grown, the InGaN quantum well layer (10) emits light in the full band from blue light to red light.

8. The preparation method according to claim 3, characterized in that: In step S10, a p-type AlGaN electron blocking layer (13) is grown on the InGaN / GaN multi-quantum well active region (8) at a temperature in the range of 830° C., wherein the thickness of the p-type AlGaN electron blocking layer (13) is between 20 nm and 30 nm; A p-type GaN layer is grown on the p-type AlGaN electron blocking layer (13) at a temperature in the range of 1140° C., wherein the thickness of the p-type GaN layer (14) is between 150 nm and 200 nm.

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