Light emitting diode chip for improving N electrode current crowding effect and preparation method thereof

Abstract

The invention discloses a light-emitting diode chip capable of improving an N electrode current crowding effect and a preparation method thereof. The chip structurally comprises a sapphire patterned substrate, a buffer layer, a stress release layer, an insulating layer, an N-type gallium nitride layer, a current expansion layer, a quantum well light-emitting layer, a P-type electron blocking layer, a P-type gallium nitride layer, a transparent conductive layer, an electrode layer and a protective layer from bottom to top. Wherein the N electrode goes deep into the N-type gallium nitride, so that the current crowding effect below the N electrode is effectively improved; besides, in order to prevent current leakage caused by the fact that current is directly injected into the N-type gallium nitride after the N electrode goes deep into the N-type gallium nitride, a current insulating layer is grown below the N-type gallium nitride to play a role in blocking the current. According to the invention, the current crowding effect of the N electrode region is effectively improved, and the current injection is improved, so that the luminous efficiency of the diode is improved.

Description

Technical Field

[0001] The invention relates to the field of LED chips, in particular to a light emitting diode chip for improving N-electrode current crowding effect and a preparation method thereof. Background Art

[0002] In the GaN-based light-emitting diode on the sapphire pattern substrate, the existence of lateral resistance causes current crowding in the local area near the edge of the N-type electrode table, resulting in uneven PN junction current, which not only affects the light-emitting performance of the device, but also has a very important impact on the reliability of the device.

[0003] In order to make the current spread evenly, it is necessary to reduce the resistance of the current channel. On the one hand, the conductivity of the N-type gallium nitride material is improved and the lateral resistance of the N-type gallium nitride is reduced; however, as the doping concentration of the N-type gallium nitride layer increases, the crystal quality will decrease, the carrier scattering effect will be aggravated, and the improvement of conductivity will be affected. Therefore, the doping concentration of the N-type gallium nitride material also needs to be controlled within a certain required range. On the other hand, the electrode pattern is optimized to reduce the lateral resistance by changing the channel path of the current; the optimized electrode pattern, combined with a suitable transparent conductive layer and current expansion layer, can better improve the current injection efficiency and injection uniformity. However, for the current channel in the area below the N electrode, the current density is still large, and the current crowding condition cannot be effectively alleviated. Summary of the invention

[0004] Purpose of the invention: In order to solve the problems existing in the prior art, the present invention provides a light-emitting diode chip and a preparation method thereof for improving the current crowding effect of the N electrode. The N electrode that penetrates deep into the N-type gallium nitride is used to better improve the current crowding effect under the N electrode; it is beneficial to improve the current injection efficiency, thereby improving the internal quantum conversion efficiency of the diode.

[0005] Technical solution: The present invention discloses a light-emitting diode chip for improving the current crowding effect of the N-electrode, which includes the following structures from bottom to top: a sapphire graphic substrate, a buffer layer, a stress release layer, an insulating layer, an N-type gallium nitride layer, a current expansion layer, a quantum well light-emitting layer, a P-type electron blocking layer, a P-type gallium nitride layer, a transparent conductive layer, an electrode layer, and a protective layer.

[0006] Furthermore, the insulating layer is grown between the stress gradient layer and the N-type gallium nitride layer. The material of the insulating layer adopts silicon nitride Si3N4 material, but is not limited to silicon nitride material. Silicon nitride material has good thermal conductivity, small thermal expansion coefficient, good electrical insulation performance, and high breakdown voltage. Therefore, it can well avoid the risk of leakage under the N electrode and enhance the electrical characteristics of the LED.

[0007] Furthermore, the N-electrode penetrates deeply into the N-type gallium nitride layer and is partially or completely embedded in the N-type gallium nitride layer, which reduces the current transport path under the traditional N-electrode, can well alleviate the current crowding effect under the N-electrode during current transport, and improve the current transport efficiency.

[0008] Furthermore, the quantum well light-emitting layer is an InGaN / GaN multi-quantum well light-emitting layer.

[0009] Furthermore, the P-type electron blocking layer is an electron blocking layer made of a P-type AlGaN material.

[0010] The present invention also discloses a method for preparing the above-mentioned light-emitting diode chip for improving the N-electrode current crowding effect, which first grows in a metal-organic chemical vapor deposition device MOCVD to obtain an LED epitaxial wafer with a complete epitaxial structure, and then prepares a flip-chip LED chip on the epitaxial wafer.

[0011] Furthermore, the steps of preparing the light emitting diode epitaxial wafer in the preparation method are as follows:

[0012] 1) Using sputtering technology to evaporate AlN material on a sapphire pattern substrate, the AlN material is a part of the buffer layer; using the sputtering technology, an AlN buffer layer material with good crystal quality can be obtained;

[0013] 2) placing the sapphire pattern substrate coated with AlN material in MOCVD for high temperature treatment, and introducing hydrogen into the high temperature chamber environment to clean the surface of the sapphire pattern substrate;

[0014] 3) growing a buffer layer on the cleaned sapphire pattern substrate in an MOCVD device;

[0015] 4) growing a stress release layer on the buffer layer in an MOCVD device;

[0016] 5) growing a silicon nitride insulating layer on the stress release layer in an MOCVD device;

[0017] 6) growing a Si-doped N-type gallium nitride layer on the silicon nitride insulating layer in an MOCVD device;

[0018] 7) growing a current spreading layer on the N-type gallium nitride layer in an MOCVD device, wherein the current spreading layer is a gallium nitride thin film material doped with low concentration Si;

[0019] 8) growing an InGaN / GaN multi-quantum well light-emitting layer on the current spreading layer in an MOCVD device;

[0020] 9) growing an electron blocking layer of a P-type AlGaN material on the InGaN / GaN quantum well light-emitting layer in an MOCVD device;

[0021] 10) Growing a Mg-doped P-type gallium nitride layer on the P-type electron blocking layer in an MOCVD device.

[0022] Furthermore, the specific method of growing the stress insulating layer and the N-type gallium nitride layer structure in the MOCVD device is as follows:

[0023] 1) Growing an insulating layer on the stress release layer structure in an MOCVD device, wherein the insulating layer material is silicon nitride Si3N4 with a thickness of The growth temperature of the silicon nitride material in the MOCVD chamber is 1000-1100°C;

[0024] 2) In the MOCVD device, Si-doped gallium nitride (GaN) is grown on the insulating layer of silicon nitride (Si3N4) described above, and the Si doping concentration of the N-type gallium nitride layer is 5×10 18 cm -3 ~5×10 19 cm -3 The growth temperature is 1050~1100℃, and the growth thickness is 1.5~3μm.

[0025] Furthermore, the preparation steps of the flip-chip LED chip are as follows:

[0026] 1) Photolithography is performed on the prepared epitaxial wafer to etch out an N electrode platform, and an N electrode hole is again photolithographically formed on the N electrode platform. The N electrode hole penetrates into the N-type gallium nitride layer, and the depth of the N electrode hole is 0.5 to 2 um;

[0027] 2) depositing a transparent conductive layer on the epitaxial wafer with the N electrode platform and the N electrode hole etched therein, and then etching away the transparent conductive layer on the N electrode platform region through a photolithography process, leaving only the transparent conductive layer on the P-type gallium nitride layer, wherein the transparent conductive layer is made of indium tin oxide (ITO) material with a thickness of Deposition growth can be carried out by using E-beam electron beam evaporation method, sputter magnetron sputtering method, or RPD reactive plasma deposition method;

[0028] 3) Depositing a metal electrode layer on the epitaxial wafer coated with the transparent conductive layer by E-beam evaporation method, wherein the material of the electrode layer is one or a combination of two or more alloys of Cr / Al / Ti / Pt / Au, and the electrode shape is designed according to the requirements;

[0029] 4) Vapor depositing a protective layer on the epitaxial wafer forming the electrode layer, wherein the protective layer material is SiO2 material and the growth thickness is PECVD equipment is used to evaporate SiO2 material, and the SiO2 protective layer plays a role of passivation protection for the entire LED chip; ultimately, a light-emitting diode chip with improved N-electrode current crowding effect is obtained.

[0030] Beneficial effects: The present invention has the following advantages:

[0031] By adopting an N-electrode structure that penetrates deep into the N-type GaN layer and partially or completely embeds it in the N-type GaN layer, the current crowding effect under the traditional N-electrode can be improved, which is beneficial to reducing the resistance of the current path under the N-electrode and the thermal effect generated, thereby improving the current injection efficiency and increasing the internal quantum efficiency of the diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic structural diagram of a light-emitting diode chip for improving the N-electrode current crowding effect in an embodiment of the present invention;

[0033] Figure 2 It is a preparation process of light-emitting diode epitaxial wafers for improving the N-electrode current crowding effect;

[0034] Figure 3 The invention relates to a preparation process of a light-emitting diode chip for improving the current crowding effect of the N-electrode.

[0035] Among them: 01-sapphire graphic substrate, 02-buffer layer, 03-stress release layer, 04-insulating layer, 05-N-type gallium nitride layer, 06-current spreading layer, 07-quantum well light-emitting layer, 08-P-type electron blocking layer, 09-P-type gallium nitride layer, 10-transparent conductive layer, 11-electrode layer (11-1 is P electrode, 11-2-1 and 11-2-2 constitute N electrode), 12-protective layer. DETAILED DESCRIPTION

[0036] Please refer to Figure 1 As shown, the present invention provides a light-emitting diode chip for improving the current crowding effect of the N-electrode and a preparation method thereof. The chip structure includes from bottom to top: a sapphire pattern substrate 01, a buffer layer 02, a stress release layer 03, an insulating layer 04, an N-type gallium nitride layer 05, a current expansion layer 06, a quantum well light-emitting layer 07, a P-type electron blocking layer 08, a P-type gallium nitride layer 09, a transparent conductive layer 10, an electrode layer 11, and a protective layer 12. The N-electrode penetrates deep into the N-type gallium nitride; and a silicon nitride insulating layer 04 is grown under the N-type gallium nitride layer 05 to play a role in blocking the current. The electrode layer 11 also includes a P-electrode 11-1 and an N-electrode 11-2-1 (11-2-2).

[0037] Specifically, in the light-emitting diode for improving the N-electrode current crowding effect, the N-electrode penetrates into the N-type gallium nitride layer 05, and is partially or completely embedded in the N-type gallium nitride layer 05, thereby improving the current transport efficiency and reducing the current crowding effect. In order to prevent the current leakage caused by the current being directly injected into the N-type gallium nitride layer 05 after the N-electrode penetrates into the N-type gallium nitride layer 05, an insulating layer 04 is first grown before the N-type gallium nitride layer 05 is grown. The material of the insulating layer 04 is silicon nitride material, but is not limited to silicon nitride material. Silicon nitride material has good thermal conductivity, small thermal expansion coefficient, good electrical insulation performance, and high breakdown voltage resistance, so it can well avoid the risk of leakage under the N-electrode, thereby enhancing the electrical characteristics of the LED.

[0038] In this embodiment, the following process flow is provided for the preparation method of the light emitting diode epitaxial wafer and chip for improving the N-electrode current crowding effect.

[0039] First, the flow chart of the epitaxial structure growth method of LED to improve the N-electrode current crowding effect is as follows: Figure 2 As shown, specifically:

[0040] 1) Sputtering technology is used to deposit AlN material on the sapphire pattern substrate 01. The AlN material is a part of the buffer layer 02, and the thickness is The sputtering technology can be used to obtain AlN material with good crystal quality;

[0041] 2) placing the sapphire pattern substrate 01 coated with AlN material into MOCVD for high temperature treatment, and introducing hydrogen into the chamber to clean the surface of the sapphire pattern substrate 01;

[0042] 3) In the MOCVD device, a buffer layer 02 is continuously grown on the sapphire pattern substrate 01 coated with AlN material; the material of the buffer layer 02 is AlGaN, the Al content is 15%, and the thickness is The growth temperature of the above AlGaN materials in the MOCVD chamber is 500-600°C;

[0043] 4) Continue to grow GaN material in two dimensions at high temperature on the material of the buffer layer 02 in the MOCVD device, the growth temperature is 900° C., and the growth thickness is 0.5-1 μm; the GaN material grown in two dimensions at high temperature serves as a nucleation layer and is part of the stress release layer 03;

[0044] 5) In the MOCVD device, a stress release layer 03 of GaN and AlGaN is then grown three-dimensionally on the high-temperature two-dimensional GaN material; the growth temperature of the three-dimensional GaN material is 1050°C, and the growth thickness is 1-3 μm; the AlGaN material has an Al doping content of 15%, a growth temperature of 1050°C, and a growth thickness of

[0045] 3) In MOCVD equipment, an insulating layer 04 is grown on the stress release layer 03. The insulating layer 04 is made of silicon nitride Si3N4 with a thickness of The growth temperature of the silicon nitride material in the MOCVD chamber is 1050°C;

[0046] 6) Growing a Si-doped N-type gallium nitride layer 05 on the insulating layer 04 in an MOCVD device; the growth temperature is 1050° C., the growth thickness is 1.5 to 3 μm, and the Si doping concentration is 5×10 18 cm -3 ~5×10 19 cm -3 ;

[0047] 7) growing a current spreading layer 06 on the N-type gallium nitride layer 05 in an MOCVD device. The current spreading layer 06 is a low-concentration Si-doped gallium nitride layer. The growth temperature is 1050° C., the growth thickness is 150 to 300 nm, and the Si doping concentration is 5×10 16 cm -3 ~5×10 17 cm -3 ;

[0048] 8) growing an InGaN / GaN multi-quantum well light-emitting layer 07 on the current spreading layer 06 in an MOCVD device; the quantum well light-emitting layer 07 is formed by alternating growth of well layer InGaN and barrier layer GaN, with a growth cycle of 5 to 15 and a growth temperature of 800° C.;

[0049] 9) In the MOCVD device, an electron blocking layer 08 of a P-type AlGaN material is grown on the InGaN / GaN quantum well light-emitting layer 07, and the thickness of the electron blocking layer 08 is The Mg doping concentration is 5×10 18 cm -3 ~5×10 19 cm -3 ;

[0050] 10) growing a p-type gallium nitride layer 09 on the p-type AlGaN electron blocking layer 08 in an MOCVD device; the p-type gallium nitride layer 09 has a thickness of The Mg doping concentration is 5×10 19 cm-3 ~5×10 20 cm -3 When the P-type GaN layer 09 is grown, rapid thermal annealing is performed on the epitaxial wafer in the MOCVD device, which is beneficial to the activation of Mg doping in the P-type GaN material, thereby improving the ohmic contact characteristics of the P-type GaN material.

[0051] Next, the preparation method of the LED chip for improving the N-electrode current crowding effect is as follows Figure 3 As shown, specifically:

[0052] 1) ICP dry etching is used on the prepared epitaxial wafer to first etch out an N electrode platform, and the etching depth of the N electrode platform is 1μm to 1.5μm; then N electrode holes are etched for the second time, and the depth of the N electrode holes (compared with the N electrode platform) is 0.5μm to 2μm; the specific method is that the epitaxial wafer with a clean surface is subjected to photoresist, exposure, and development in the yellow light area, the mask layer pattern of MESA is copied to the surface of the epitaxial wafer, and then the ICP equipment is used for dry etching to etch the area not covered by the mask layer to the N-GaN layer, so as to obtain the N electrode table and the cutting road between the core particles, and after the etching is completed, the surface residual photoresist, i.e., the mask layer, is cleaned and removed.

[0053] 2) Etching the N electrode hole on the wafer with the N electrode platform etched, the specific method is to spin dry the moisture on the wafer surface after degumming, perform photoresist coating, exposure and development in the yellow light area, copy the mask layer pattern of the N electrode hole to the wafer surface, and use the ICP equipment for dry etching again, and etch the area not covered by the mask layer to the designed depth, so as to obtain the N electrode hole embedded in the n-type gallium nitride layer. After the etching is completed, the surface residual photoresist is removed by cleaning.

[0054] 3) Depositing a transparent conductive layer 10 on the epitaxial wafer with the N electrode platform and the N electrode hole etched therein, wherein the transparent conductive layer 10 is made of indium tin oxide (ITO) material with a thickness of The ITO transparent conductive film can be grown by E-beam electron beam evaporation, sputter magnetron sputtering coating, or RPD reactive plasma deposition. The appropriate evaporation method is selected according to the photoelectric characteristics of the LED chip. In this embodiment, the sputter magnetron sputtering coating method is used to deposit the indium tin oxide ITO material. The sputter magnetron sputtering method can obtain an ITO film layer with good density and relatively stable resistance. Then, the yellow light area is used for coating, exposure, and development to obtain the required pattern on the transparent conductive layer 10. The ITO layer on the N-electrode table and the core particle cutting path is removed by wet etching to expose the N-electrode table and the core particle cutting path. After that, the residual mask layer on the surface is removed by cleaning. After the above steps, the core particle obtained has its P-type gallium nitride material, that is, the P-electrode table covered by the ITO layer.

[0055] 4) An N electrode 11-2-1 (i.e., the electrode portion embedded in the N-type gallium nitride layer) is deposited in the N electrode hole by an E-beam evaporation method, wherein the material of the electrode layer 11-2-1 is one of Al / Ni / Pt / Au or an alloy combination; a specific method is to perform photoresist coating, exposure, and development in the yellow light area to form a desired electrode pattern on the wafer, and then use an electron beam evaporation device to perform film evaporation of the N electrode 11-2-1, and then peel off the gold to remove the photoresist.

[0056] 5) Then, the electrode 11-2-2 on the N electrode platform and the P electrode layer 11-1 are evaporated for a second time. The material of the electrode 11-2-1 on the N electrode platform and the P electrode layer 11-1 is an alloy combination of Cr / Al / Ti / Pt / Au. The specific method is to perform photoresist coating, exposure, and development in the yellow light area to form the required electrode pattern on the transparent conductive layer 10 and the N electrode 11-2-1, and then use electron beam evaporation equipment to evaporate the film layer of the P electrode 11-1 and the N electrode 11-2-2, and then peel off the gold and remove the glue.

[0057] 6) Vapor-depositing a chip protective layer 12 on the epitaxial wafer forming the electrode layer, wherein the protective layer material is silicon dioxide, and the PECVD method is used for vapor deposition, and the film thickness is The specific method is to first use PECVD equipment to evaporate the silicon dioxide protective layer 12, then perform photoresist, exposure, and development in the yellow light area to form the required protective layer pattern on the wafer surface (the mask layer exposes the N electrode 11-2-2 and P electrode 11-1 areas), and then use wet etching to remove the silicon dioxide protective layer material on the N electrode 11-2-2 and P electrode 11-1, and then perform photoresist removal and cleaning. Finally, a light-emitting diode chip with improved N electrode current crowding effect is obtained.

[0058] The present invention adopts an N-electrode structure that penetrates deep into the N-type gallium nitride and is partially or completely embedded in the N-type gallium nitride layer, thereby effectively improving the current crowding effect under the traditional N-electrode, and is conducive to reducing the resistance of the current path under the N-electrode and the generated thermal effect, thereby improving the current injection efficiency and increasing the light extraction rate of the diode. Before growing the N-type gallium nitride, a silicon nitride material insulating layer is first grown. Since the silicon nitride material has good thermal conductivity, small thermal expansion coefficient, good electrical insulation performance, and high breakdown voltage, it can well avoid the risk of leakage under the N-electrode that penetrates deep into the N-type gallium nitride, and further enhance the electrical characteristics of the LED.

Claims

1. A light-emitting diode chip for improving the N-electrode current crowding effect, characterized in that From bottom to top, it includes the following structures: sapphire graphic substrate, buffer layer, stress release layer, insulating layer, N-type gallium nitride layer, current spreading layer, quantum well light-emitting layer, P-type electron blocking layer, P-type gallium nitride layer, transparent conductive layer, electrode layer, and protective layer.

2. The light emitting diode chip for improving N-electrode current crowding effect according to claim 1, characterized in that: The insulating layer material is silicon nitride material.

3. The light emitting diode chip for improving N-electrode current crowding effect according to claim 1, characterized in that: An N-electrode is deeply embedded in the N-type gallium nitride layer, and the N-electrode is partially or completely embedded in the N-type gallium nitride layer.

4. The light emitting diode chip for improving N-electrode current crowding effect according to claim 1, characterized in that: The quantum hydrazine light-emitting layer is an InGaN / GaN multi-quantum well light-emitting layer.

5. The light emitting diode chip for improving N-electrode current crowding effect according to claim 1, characterized in that: The P-type electron blocking layer is an electron blocking layer made of a P-type AlGaN material.

6. A method for preparing a light-emitting diode chip for improving N-electrode current crowding effect according to any one of claims 1 to 5, characterized in that First, it is grown in a metal-organic chemical vapor deposition device MOCVD to obtain an LED epitaxial wafer with a complete epitaxial structure, and then a flip-chip LED chip is prepared on the epitaxial wafer.

7. The method for preparing a light emitting diode chip for improving the N-electrode current crowding effect according to claim 6, characterized in that The preparation steps of light-emitting diode epitaxial wafer are as follows: 1) using a sputtering technique to evaporate AlN material on a sapphire pattern substrate, wherein the AlN material is a part of the buffer layer; 2) placing the sapphire pattern substrate coated with AlN material in MOCVD for high temperature treatment, and introducing hydrogen into the high temperature chamber environment to clean the surface of the sapphire pattern substrate; 3) growing a buffer layer on the cleaned sapphire pattern substrate in an MOCVD device; 4) growing a stress release layer on the buffer layer in an MOCVD device; 5) growing a silicon nitride insulating layer on the stress release layer in an MOCVD device; 6) growing a Si-doped N-type gallium nitride layer on the silicon nitride insulating layer in an MOCVD device; 7) growing a current spreading layer on the N-type gallium nitride layer in an MOCVD device, wherein the current spreading layer is a gallium nitride thin film material doped with low concentration Si; 8) growing an InGaN / GaN multi-quantum well light-emitting layer on the current spreading layer in an MOCVD device; 9) growing an electron blocking layer of a P-type AlGaN material on the InGaN / GaN quantum well light-emitting layer in an MOCVD device; 10) Growing a Mg-doped P-type gallium nitride layer on the P-type electron blocking layer in an MOCVD device.

8. The method for preparing a light emitting diode chip for improving the N-electrode current crowding effect according to claim 7, characterized in that The specific method of growing the stress insulating layer and the N-type gallium nitride layer structure in the MOCVD equipment is as follows: 1) Growing an insulating layer on the stress release layer structure in an MOCVD device, wherein the insulating layer material is silicon nitride Si3N4 with a thickness of The growth temperature of the silicon nitride material in the MOCVD chamber is 1000-1100°C; 2) In the MOCVD device, Si-doped gallium nitride (GaN) is grown on the insulating layer of silicon nitride (Si3N4) described above, and the Si doping concentration of the N-type gallium nitride layer is 5×10 18 cm -3 ~5×10 19 cm -3 The growth temperature is 1050~1100℃, and the growth thickness is 1.5~3μm.

9. The method for preparing a light emitting diode chip for improving the N-electrode current crowding effect according to claim 6, characterized in that The preparation steps of flip-chip LED chip are as follows: 1) Photolithography is performed on the prepared epitaxial wafer to etch out an N electrode platform, and an N electrode hole is again photolithographically formed on the N electrode platform. The N electrode hole penetrates into the N-type gallium nitride layer, and the depth of the N electrode hole is 0.5 to 2 um; 2) depositing a transparent conductive layer on the epitaxial wafer with the N electrode platform and the N electrode hole etched therein, and then etching away the transparent conductive layer on the N electrode platform region through a photolithography process, leaving only the transparent conductive layer on the P-type gallium nitride layer, wherein the transparent conductive layer is made of indium tin oxide (ITO) material with a thickness of Deposition growth can be carried out by using E-beam electron beam evaporation method, sputter magnetron sputtering method, or RPD reactive plasma deposition method; 3) Depositing a metal electrode layer on the epitaxial wafer coated with the transparent conductive layer by E-beam evaporation method, wherein the material of the electrode layer is one or a combination of two or more alloys of Cr / Al / Ti / Pt / Au, and the electrode shape is designed according to the requirements; 4) Vapor depositing a protective layer on the epitaxial wafer forming the electrode layer, wherein the protective layer is made of SiO2 material and has a growth thickness of PECVD equipment is used to evaporate SiO2 material, and finally a light-emitting diode chip with improved N-electrode current crowding effect is obtained.

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