GaN-LED epitaxial wafer surface roughening method, epitaxial wafer and LED

Abstract

This invention relates to the field of semiconductor technology, specifically disclosing a method for roughening the surface of a GaN-LED epitaxial wafer, the epitaxial wafer, and an LED. The method includes: providing a substrate; growing a GaN epitaxial layer on the substrate; covering the surface of the GaN epitaxial layer with a sealing film layer; and irradiating the GaN epitaxial layer covered with the sealing film layer using a laser beam. The sealing film layer has a bandgap wider than the GaN epitaxial layer, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer and the bandgap of the sealing film layer. The surface roughening method of this invention is simple, requires low equipment precision, has high processing efficiency, is easy to implement, and has low production costs.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials technology, and in particular to a method for roughening the surface of a GaN-LED epitaxial wafer, the epitaxial wafer, and the LED. Background Technology

[0002] Currently, GaN-based blue and blue-green light-emitting devices are developing very rapidly. As a third-generation semiconductor with excellent characteristics, it has advantages such as wide bandgap, high breakdown electric field, high electron saturation drift velocity, and fast electron migration rate. It is widely used in optoelectronic devices, especially in blue-green light-emitting diodes.

[0003] High-brightness LEDs have always been a goal, and the brightness of an LED depends on its luminous efficiency. With the continuous optimization of epitaxial processes, the internal quantum efficiency of LED chips has reached its limit, while the external quantum efficiency remains relatively low.

[0004] Currently, many methods have been developed to improve external quantum efficiency, including the use of coupling between surface plasmons and semiconductors, chip shape modification, resonant cavities, surface roughening, photonic crystals, and patterned substrate technology. Among these, surface roughening is the most economical and easiest technology to integrate with current LED processes.

[0005] In recent years, several methods have been developed to improve external quantum efficiency by altering surface roughness through post-processing techniques, such as wet etching and ICP dry etching. However, these methods suffer from complex operation, cumbersome processes, and high costs. In addition, there is a method using lasers for patterned surface roughening etching. This method employs a focused laser beam combined with high-precision electric displacement to pattern and roughen the epitaxial wafer. The laser decomposes GaN at fixed positions to achieve patterned etching on the epitaxial wafer surface, similar to ICP etching. Although this method simplifies the operation process compared to wet etching and ICP dry etching, it still requires extremely high equipment precision and has high equipment costs, resulting in high costs and complex processes. Furthermore, it leaves a large amount of Ga residue on the surface, which oxidizes and is difficult to dissolve with conventional acidic solutions, significantly impacting the electrical properties of the manufactured LEDs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for roughening the surface of GaN-LED epitaxial wafers, as well as the epitaxial wafers and LEDs, in view of the existing technical status. The surface roughening method of this invention is simple in process, has low equipment precision requirements, high processing efficiency, is easy to implement, and has low production cost.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] As one of the objectives of this invention, this invention discloses a method for roughening the surface of a GaN-LED epitaxial wafer, comprising:

[0009] Provide a substrate;

[0010] A GaN epitaxial layer is grown on the substrate;

[0011] A sealing film layer is applied to the surface of the GaN epitaxial layer;

[0012] The GaN epitaxial layer covered with the sealing film was irradiated with a laser beam;

[0013] Wherein, the bandgap of the sealing film layer is higher than the bandgap of the GaN epitaxial layer, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer and the bandgap of the sealing film layer.

[0014] In some embodiments, the sealing film layer has an irradiation area for the laser beam to irradiate and a non-irradiation area located around the irradiation area.

[0015] In some embodiments, the bandgap of the GaN epitaxial layer is 3.4 eV, and the bandgap of the sealing film layer is ≥6 eV.

[0016] In some embodiments, the energy density of the laser beam is ≥400 mJ / cm². 2 .

[0017] In some embodiments, the sealing film layer is a silicon oxide sealing film layer or an aluminum oxide sealing film layer.

[0018] In some embodiments, the sealing film layer is prepared by any one of vapor deposition, magnetron sputtering, or plasma-enhanced chemical deposition.

[0019] In some embodiments, the thickness of the sealing film layer is

[0020] In some embodiments, the method further includes: etching the epitaxial wafer irradiated by the laser beam in a buffer oxide etching solution, wherein the ratio of HF to NH4F in the buffer oxide etching solution is 1:20.

[0021] As another objective of this invention, this invention discloses an epitaxial wafer prepared according to the above-described GaN-LED epitaxial wafer surface roughening method.

[0022] As another objective of this invention, this invention discloses an LED comprising the epitaxial wafer described above.

[0023] The beneficial effects of this invention are as follows:

[0024] In this invention, a dense sealing film layer is coated on the surface of the GaN epitaxial layer. The sealing film layer is made of a material with a bandgap wider than that of the GaN epitaxial layer. During roughening, a laser beam is used to irradiate the epitaxial wafer from the outside of the sealing film layer, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer and the bandgap of the sealing film layer. At this time, the laser beam is absorbed by the GaN of the epitaxial wafer at the interface between the sealing film layer and the GaN epitaxial layer, decomposing into N2 gas. The sealing film layer retains the N2 gas at the interface. As the bubbles accumulate and increase, a huge pressure is generated, which tears the surface of the GaN epitaxial layer, thereby roughening the surface of the GaN epitaxial layer. The surface roughening method of this invention is simple in process, has low requirements for the irradiation accuracy and beam spot size of the laser beam, does not require high-precision equipment, and can use a large-size beam spot for scanning irradiation. In addition, the sealing film layer can also seal and protect the surface of the GaN epitaxial layer, effectively preventing Ga from being oxidized and reducing the difficulty of subsequent Ga removal. The overall processing efficiency is high, easy to implement, and has low production cost. It can also be applied to large-area roughening treatment. After the epitaxial wafer is roughened by the surface roughening method of this invention, the light emission probability is improved, thereby improving the external quantum efficiency. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the principle of the GaN-LED epitaxial wafer surface roughening method of the present invention.

[0026] Figure 2 This is a schematic diagram of the surface of the epitaxial wafer prepared in Example 1.

[0027] Figure 3 This is a schematic diagram of the surface of the epitaxial wafer prepared in Example 2.

[0028] Figure 4 This is a schematic diagram of the surface of the epitaxial wafer prepared in Comparative Example 1.

[0029] Figure 5 This is a schematic diagram of the surface of the epitaxial wafer prepared in Comparative Example 2. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below:

[0031] Please see Figure 1 As shown, this invention discloses a method for roughening the surface of a GaN-LED epitaxial wafer, comprising:

[0032] Provide a substrate;

[0033] A GaN epitaxial layer 1 is grown on the substrate;

[0034] A sealing film layer 2 is applied to the surface of the GaN epitaxial layer 1;

[0035] In this process, a laser beam is used to irradiate the GaN epitaxial layer 1 covered with a sealing film layer 2.

[0036] The bandgap of the sealing film layer 2 is higher than that of the GaN epitaxial layer 1, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer 1 and the bandgap of the sealing film layer 2.

[0037] In this invention, a dense sealing film layer 2 is coated on the surface of the GaN epitaxial layer 1, and the material of the sealing film layer 2 is selected with a bandgap wider than that of the GaN epitaxial layer 1. During roughening, a laser beam is used to irradiate the epitaxial wafer from the outside of the sealing film layer 2, and the photon energy of the laser beam is made to be between the bandgap of the GaN epitaxial layer 1 and the bandgap of the sealing film layer 2. At this time, the laser beam will not be absorbed by the sealing film layer 2, but will be mainly absorbed by the GaN of the epitaxial wafer at the junction of the sealing film layer 2 and the GaN epitaxial layer 1. The GaN is decomposed into Ga and N2. The N2 gas released from the decomposition is covered by the sealing film layer 2 and cannot escape, so that the N2 gas is kept at the junction. As the bubbles accumulate and increase, a huge pressure is generated, which tears the surface of the GaN epitaxial layer 1, thereby roughening the surface of the GaN epitaxial layer 1.

[0038] The surface roughening method of the present invention is simple in process, has low requirements for the irradiation accuracy and beam spot size of the laser beam, does not require high-precision equipment, and can use a large-size beam spot for scanning irradiation. In addition, the sealing film layer 2 can also provide sealed protection for the surface of GaN epitaxial layer 1, effectively preventing Ga from being oxidized and reducing the difficulty of subsequent Ga removal. The overall processing efficiency is high, easy to implement, and has low production cost. It can also be applied to large-area roughening treatment. After the epitaxial wafer is roughened by the surface roughening method of the present invention, the light emission probability is improved, thereby improving the external quantum efficiency.

[0039] The sealing film layer 2 has an irradiation area for laser beam irradiation and a non-irradiation area surrounding the irradiation area. During roughening, the laser beam does not irradiate the non-irradiation area, thereby ensuring the formation of a sealed space at the interface between the sealing film layer 2 and the epitaxial layer. This prevents the gas decomposed during irradiation from escaping from the surrounding area, further improving the roughening effect. At the same time, it further prevents the decomposed Ga from being oxidized, avoiding the increased difficulty of Ga removal due to Ga oxidation.

[0040] The bandgap of the GaN epitaxial layer 1 is 3.4 eV, and the bandgap of the sealing film layer 2 is ≥6 eV. More preferably, the bandgap of the sealing film layer 2 is ≥8 eV, so as to ensure that the bandgap of the sealing film layer 2 is much higher than the bandgap of the GaN epitaxial layer 1. The laser beam can be absorbed by the GaN epitaxial layer 1 as much as possible, and the energy selection range of the laser beam is larger and easier to implement. Moreover, the energy of the laser beam can be adjusted within the operating range according to different needs to obtain different roughening degrees.

[0041] Among them, the energy density of the laser beam is ≥400mJ / cm². 2 For example, the energy density of the laser beam is 400 mJ / cm². 2 450mJ / cm 2 500mJ / cm 2 Or 550mJ / cm 2 However, this is not the only factor. Different laser energy densities result in different gas quantities, which in turn produce different gas pressures, affecting the final roughening degree. Experiments have shown that a laser beam energy density ≥400 mJ / cm² is optimal. 2 This ensures that the energy density reaches the decomposition threshold of GaN, thus guaranteeing that GaN decomposes.

[0042] Preferably, the sealing film layer 2 is a silicon oxide sealing film layer or an aluminum oxide sealing film layer, wherein the band gap of the silicon oxide sealing film layer is 8 eV and the band gap of the aluminum oxide sealing film layer is 8.8 eV. More preferably, the sealing film layer 2 is a silicon oxide sealing film layer. Compared with the aluminum oxide sealing film layer, the silicon oxide sealing film layer is easier to remove, while the aluminum oxide sealing film layer requires a certain level of laser energy to achieve laser ablation.

[0043] The sealing film layer 2 is prepared by any one of vapor deposition, magnetron sputtering, or plasma-enhanced chemical deposition. The density of the sealing film layer 2 prepared by each method is in the following order: vapor deposition < magnetron sputtering < plasma-enhanced chemical deposition. Preferably, the sealing film layer 2 is prepared by plasma-enhanced chemical deposition. The higher the density of the sealing film layer 2, the better the gas encapsulation, and the easier it is to form a roughened structure on the surface of the GaN epitaxial layer 1.

[0044] The thickness of the sealing film layer 2 is... For example, the thickness of the sealing film layer 2 is or However, this is not the only issue. If the thickness of the sealing membrane layer 2 is too small, it may result in poor gas encapsulation or poor gas pressure resistance. If the thickness of the sealing membrane layer 2 is too large, it may increase the difficulty of removing the sealing membrane layer 2 in the future.

[0045] Preferably, the irradiation method is scanning irradiation. Since the present invention has low requirements for the irradiation accuracy of the laser beam, scanning irradiation can be selected to further improve the processing efficiency.

[0046] This invention discloses an epitaxial wafer, which is prepared according to the above-mentioned GaN-LED epitaxial wafer surface roughening method. After the epitaxial wafer is roughened by the surface roughening method of this invention, the light emission probability is improved, thereby improving the external quantum efficiency.

[0047] This invention discloses an LED comprising the epitaxial wafer described above.

[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0049] Example 1

[0050] A method for roughening the surface of a GaN-LED epitaxial wafer includes:

[0051] S10. Provide a substrate;

[0052] S20. Grow GaN epitaxial layer 1 on the substrate, the specific steps of which are as follows:

[0053] A substrate is provided, on which a buffer layer, an undoped semiconductor layer, an N-type conductor layer, a multiple quantum well layer, an electron blocking layer, and a GaN epitaxial layer 1 are sequentially grown.

[0054] S30. Cover the surface of the GaN epitaxial layer 1 with a sealing film layer 2, the specific steps of which are as follows:

[0055] A silicon oxide sealing film was grown on GaN epitaxial layer 1 using plasma-enhanced chemical deposition. The thickness of the silicon oxide sealing film was [missing information].

[0056] S40. The GaN epitaxial layer 1 covered with the sealing film layer 2 is irradiated with a laser beam, wherein the energy density of the laser beam is 500 mJ / cm². 2 The irradiation method is scanning irradiation. During the irradiation process, the non-irradiated areas are not irradiated. In this embodiment, the outer 3mm of the sealing film layer 2 is the non-irradiated area.

[0057] The bandgap of the sealing film layer 2 is higher than that of the GaN epitaxial layer 1, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer 1 and the bandgap of the sealing film layer 2.

[0058] S50. The irradiated epitaxial wafer is placed in a 29°C BOE solution for etching, wherein the HF:NH4F ratio in the BOE solution is 1:20, and the etching time is 650s. The silicon oxide sealing film and the decomposed Ga are removed together by the BOE solution. Then, the residual solution on the surface of the epitaxial wafer can be removed with water.

[0059] After the epitaxial wafer has undergone the above surface roughening treatment, it can be processed into subsequent conventional processing steps.

[0060] Example 2

[0061] A method for roughening the surface of a GaN-LED epitaxial wafer includes:

[0062] S10. Provide a substrate;

[0063] S20. Grow GaN epitaxial layer 1 on the substrate, the specific steps of which are as follows:

[0064] A substrate is provided, on which a buffer layer, an undoped semiconductor layer, an N-type conductor layer, a multiple quantum well layer, an electron blocking layer, and a GaN epitaxial layer 1 are sequentially grown.

[0065] S30. Cover the surface of the GaN epitaxial layer 1 with a sealing film layer 2, the specific steps of which are as follows:

[0066] A silicon oxide sealing film was grown on GaN epitaxial layer 1 using plasma-enhanced chemical deposition. The thickness of the silicon oxide sealing film was [missing information].

[0067] S40. The GaN epitaxial layer 1 covered with the sealing film layer 2 is irradiated with a laser beam, wherein the energy density of the laser beam is 400 mJ / cm². 2 The irradiation method is scanning irradiation. During the irradiation process, the non-irradiated areas are not irradiated. In this embodiment, the outer 3mm of the sealing film layer 2 is the non-irradiated area.

[0068] The bandgap of the sealing film layer 2 is higher than that of the GaN epitaxial layer 1, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer 1 and the bandgap of the sealing film layer 2.

[0069] S50. The irradiated epitaxial wafer is placed in a 29°C BOE solution for etching, wherein the HF:NH4F ratio in the BOE solution is 1:20, and the etching time is 650s. The silicon oxide sealing film and the decomposed Ga are removed together by the BOE solution. Then, the residual solution on the surface of the epitaxial wafer can be removed with water.

[0070] After the epitaxial wafer has undergone the above surface roughening treatment, it can be processed into subsequent conventional processing steps.

[0071] Example 3

[0072] A method for roughening the surface of a GaN-LED epitaxial wafer includes:

[0073] S10. Provide a substrate;

[0074] S20. Grow GaN epitaxial layer 1 on the substrate, the specific steps of which are as follows:

[0075] A substrate is provided, on which a buffer layer, an undoped semiconductor layer, an N-type conductor layer, a multiple quantum well layer, an electron blocking layer, and a GaN epitaxial layer 1 are sequentially grown.

[0076] S30. Cover the surface of the GaN epitaxial layer 1 with a sealing film layer 2, the specific steps of which are as follows:

[0077] An alumina sealing film was grown on GaN epitaxial layer 1 using plasma-enhanced chemical deposition. The thickness of the alumina sealing film was [missing information].

[0078] S40. The GaN epitaxial layer 1 covered with the sealing film layer 2 is irradiated with a laser beam, wherein the energy density of the laser beam is 500 mJ / cm². 2 The irradiation method is scanning irradiation. During the irradiation process, the non-irradiated areas are not irradiated. In this embodiment, the outer 3mm of the sealing film layer 2 is the non-irradiated area.

[0079] The bandgap of the sealing film layer 2 is higher than that of the GaN epitaxial layer 1, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer 1 and the bandgap of the sealing film layer 2.

[0080] After the epitaxial wafer has undergone the above surface roughening treatment, it can be processed into subsequent conventional processing steps.

[0081] S50. The irradiated epitaxial wafer is placed in a 29°C BOE solution for etching, wherein the HF:NH4F ratio in the BOE solution is 1:20, and the etching time is 800s. The silicon oxide sealing film and the decomposed Ga are removed together by the BOE solution. Then, the residual solution on the surface of the epitaxial wafer can be removed with water.

[0082] Comparative Example 1

[0083] A method for roughening the surface of a GaN-LED epitaxial wafer includes:

[0084] S10. Provide a substrate;

[0085] S20. Grow a GaN epitaxial layer on the substrate, the specific steps of which are as follows:

[0086] A substrate is provided, on which a buffer layer, an undoped semiconductor layer, an N-type conductor layer, a multiple quantum well layer, an electron blocking layer, and a GaN epitaxial layer are grown sequentially.

[0087] S30. Cover the surface of the GaN epitaxial layer with a sealing film layer, the specific steps of which are as follows:

[0088] A silicon oxide sealing film was grown on a GaN epitaxial layer using plasma-enhanced chemical deposition. The thickness of the silicon oxide sealing film was [missing information].

[0089] S40. A laser beam is used to irradiate the GaN epitaxial layer covered with a sealing film, wherein the energy density of the laser beam is 400 mJ / cm². 2 The irradiation method is scanning irradiation. During the irradiation process, the non-irradiated areas are not preserved, that is, the non-irradiated areas are also irradiated.

[0090] The bandgap of the sealing film is higher than that of the GaN epitaxial layer, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer and the bandgap of the sealing film.

[0091] S50. The irradiated epitaxial wafer is placed in a 29°C BOE solution for etching, wherein the HF:NH4F ratio in the BOE solution is 1:20, and the etching time is 650s. The silicon oxide sealing film and the decomposed Ga are removed together by the BOE solution. Then, the residual solution on the surface of the epitaxial wafer can be removed with water.

[0092] After the epitaxial wafer has undergone the above surface roughening treatment, it can be processed into subsequent conventional processing steps.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 1 is that step S40 is not performed.

[0095] The surface appearance of the epitaxial wafers prepared in Examples 1-3 and Comparative Examples 1-2 was compared, and the external quantum efficiency of each experimental group was tested. The percentage improvement of external quantum efficiency of Examples 1-3 and Comparative Example 1 compared with Comparative Example 2 was compared as follows:

[0096] experimental group Apparent situation Percentage improvement in external quantum efficiency Example 1 The epitaxial wafer surface exhibits a distinct roughening structure. 9.0％ Example 2 The epitaxial wafer surface exhibits a distinct roughening structure. 6.0％ Example 3 The epitaxial wafer surface exhibits a distinct roughening structure. 7.0％ Comparative Example 1 Fine coarsening structure is produced on the surface of the epitaxial wafer. 3.0％ Comparative Example 2 The epitaxial wafer surface has no roughened structure -

[0097] Combined with Table 1 and appendix Figures 2-5 As shown, the surface of the epitaxial wafers prepared in Examples 1 to 3 all exhibited obvious roughened structures after being treated by the surface roughening method of the present invention. Among them, the surface roughness of Example 1 was the largest. Although the surface of the epitaxial wafer prepared in Comparative Example 1 also had a roughened structure, its roughness was relatively fine, which was inferior to that of the epitaxial wafers prepared in Examples 1 to 3. The reason for this is that during the irradiation process, the non-irradiated area was not retained, resulting in gas escape and insufficient gas volume, which affected the final roughening result.

[0098] Of course, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for roughening the surface of a GaN-LED epitaxial wafer, characterized in that, include: Provide a substrate; A GaN epitaxial layer is grown on the substrate; A sealing film layer is applied to the surface of the GaN epitaxial layer; The GaN epitaxial layer covered with the sealing film was irradiated with a laser beam; Wherein, the bandgap of the sealing film layer is higher than the bandgap of the GaN epitaxial layer, and the photon energy of the laser beam is between the bandgap of the GaN epitaxial layer and the bandgap of the sealing film layer.

2. The method for roughening the surface of a GaN-LED epitaxial wafer according to claim 1, characterized in that, The sealing film layer has an irradiation area for the laser beam to irradiate and a non-irradiation area located around the irradiation area.

3. The method for roughening the surface of a GaN-LED epitaxial wafer according to claim 1, characterized in that, The bandgap of the GaN epitaxial layer is 3.4 eV, and the bandgap of the sealing film layer is ≥6 eV.

4. The method for roughening the surface of a GaN-LED epitaxial wafer according to claim 3, characterized in that, The energy density of the laser beam is ≥400 mJ / cm² 2 .

5. The method for roughening the surface of a GaN-LED epitaxial wafer according to claim 1, characterized in that, The sealing film layer is a silicon oxide sealing film layer or an aluminum oxide sealing film layer.

6. The method for roughening the surface of a GaN-LED epitaxial wafer according to claim 1, characterized in that, The sealing film layer is prepared by any one of the following methods: vapor deposition, magnetron sputtering, or plasma-enhanced chemical deposition.

7. The method for roughening the surface of a GaN-LED epitaxial wafer according to claim 1, characterized in that, The thickness of the sealing film layer is 8. The method for roughening the surface of a GaN-LED epitaxial wafer according to claim 1, characterized in that, The irradiation method is scanning irradiation.

9. An epitaxial wafer, characterized in that, The GaN-LED epitaxial wafer is prepared by the surface roughening method according to any one of claims 1 to 8.

10. An LED, characterized in that, Includes the epitaxial wafer according to claim 9.

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