Light emitting diode with side wall microstructure and preparation method thereof

Abstract

The invention relates to a light-emitting diode with a side wall microstructure and a preparation method thereof, and belongs to the field of photoelectrons. The multi-quantum well multi-quantum well solar cell comprises a permanent substrate ohmic contact electrode, a permanent substrate, a reflector, a dielectric film, a P-type ohmic contact layer, a P-GaP ohmic contact layer, a P-AlGaInP current expansion layer, a P-AlInP limiting layer, an MQW multi-quantum well layer, an N-AlInP limiting layer, an N-AlGaInP current expansion layer, an N-AlGaInP coarsening layer, an N-GaAs ohmic contact layer and an N-surface electrode in sequence from bottom to top. The standing wave effect is utilized, the exposure and development time of the photoresist and the hardening temperature are optimized, the photoresist with the side wall microstructure is formed, then the photoresist is utilized as a mask, the GaP is etched through ICP, the side wall microstructure on the photoresist is copied to the GaP in the etching process, the side wall light emitting area is increased while the total reflection of an interface is reduced through the microstructure, and the light emitting efficiency is improved. And the brightness is improved.

Description

Technical Field

[0001] The invention relates to a light emitting diode with a side wall microstructure and a preparation method thereof, belonging to the technical field of optoelectronics. Background Art

[0002] As one of the most valued light source technologies, LED has the characteristics of small size on the one hand; on the other hand, it has the power-saving characteristics of low current and low voltage drive; at the same time, it also has many advantages such as strong structure, strong impact and vibration resistance, and ultra-long life. Quaternary AIGaInP is a semiconductor material with a direct wide band gap, which has been widely used in the preparation of various optoelectronic devices. Since the luminous band of AIGaInP material can cover the red to yellow-green band of visible light, the visible light emitting diodes made from it have received widespread attention. Light emitting diodes, especially AlGaInP (quaternary system) red high-brightness light emitting diodes have been widely used in many aspects such as outdoor display, monitoring lighting, and car lights.

[0003] At present, for quaternary AlGaInP reverse polarity light-emitting diodes, AlGaInP roughening, segmented etching and other processes are generally used to improve their brightness. When segmented etching is used, the side wall formed by the second etching will absorb part of the photons due to total reflection, resulting in reduced brightness. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a light-emitting diode with a sidewall microstructure and a preparation method thereof. The preparation method utilizes the standing wave effect to optimize and adjust the exposure, development time and hardening temperature of the photoresist to form a photoresist with a sidewall microstructure. Then, the photoresist is used as a mask and GaP is etched by ICP. During the etching process, the sidewall microstructure on the photoresist is copied to GaP. The microstructure reduces the total reflection at the interface and increases the light emitting area of ​​the sidewall, thereby improving the brightness.

[0005] Terminology explanation:

[0006] Standing wave effect: When the photoresist is exposed, light passes through the photoresist and shines on the silicon (Si) substrate. At the interface between the photoresist and the substrate, the light will be reflected. These reflected lights and the incident light will interfere with each other, making the light intensity unevenly distributed along the depth of the photoresist, forming a standing wave effect.

[0007] The technical solution of the present invention is as follows:

[0008] A light emitting diode with a sidewall microstructure comprises, from bottom to top, a permanent substrate ohmic contact electrode, a permanent substrate, a reflector, a dielectric film, a P-type ohmic contact layer, a P-GaP ohmic contact layer, a P-AlGaInP current expansion layer, a P-AlInP restriction layer, an MQW multi-quantum well layer, an N-AlInP restriction layer, an N-AlGaInP current expansion layer, an N-AlGaInP roughening layer, an N-GaAs ohmic contact layer and an N-surface electrode, wherein the GaP of the P-GaP ohmic contact layer has a photoresist with a sidewall microstructure.

[0009] A method for preparing the above-mentioned light-emitting diode with sidewall microstructure comprises the following steps:

[0010] (1) using a MOCVD method, an N-GaAs buffer layer, an N-GaInP barrier layer, an N-GaAs ohmic contact layer, an N-AlGaInP roughening layer, an N-AlGaInP current spreading layer, an N-AlInP confinement layer, an MQW multi-quantum well layer, a P-AlInP confinement layer, a P-AlGaInP current spreading layer and a P-GaP ohmic contact layer are sequentially grown on an n-GaAs temporary substrate;

[0011] (2) depositing a dielectric film on the P-GaP ohmic contact layer of the epitaxial wafer in step (1), and then performing photolithography, evaporation, etching, and stripping processes to form a P-type ohmic contact layer;

[0012] (3) evaporating a reflector on the surface of the wafer obtained in step (2);

[0013] (4) bonding the wafer obtained in step (3) to a permanent substrate;

[0014] (5) removing the n-GaAs temporary substrate, N-GaAs buffer layer and N-GaInP barrier layer of the wafer after bonding;

[0015] (6) Etching the N-GaAs ohmic contact layer outside the electrode area;

[0016] (7) evaporating an N-side electrode on the N-GaAs ohmic contact layer retained in step (6), and forming an ohmic contact through an alloy process;

[0017] (8) performing photolithography to cut the wafer obtained in step (7) to form a cutting pattern, and after hardening the film, using ICP etching to form a cutting line;

[0018] (9) roughening the wafer obtained in step (8) on the N-AlGaInP roughening layer;

[0019] (10) using photolithography and ICP etching to form a secondary etching pattern on GaP in the cut road, optimizing and adjusting the exposure and development time and hardening temperature of the photoresist to form a photoresist with a sidewall microstructure;

[0020] (11) thinning the permanent substrate, and then evaporating an ohmic contact metal and forming an alloy to form an ohmic contact electrode on the permanent substrate;

[0021] (12) Light-emitting diodes are obtained by laser scribing or diamond knife cutting.

[0022] Preferably, in step (2), the dielectric film is a SiO2 dielectric film.

[0023] Preferably, in step (3), the reflecting mirror is a gold mirror or a silver mirror.

[0024] Preferably, in step (4), the bonding method is Au-Au bonding or Au-In bonding, the bonding temperature is 200-350° C., the pressure is 200-500 kg, and the time is 30-50 min.

[0025] Preferably, in step (5), a mixed solution of ammonia water, hydrogen peroxide and water is used to remove the temporary n-GaAs substrate of the wafer after bonding; in the mixed solution, the volume ratio of ammonia water, hydrogen peroxide and water is 1:4:5.

[0026] Preferably, in step (5), the N-GaInP barrier layer is removed by using a mixed solution of hydrochloric acid and water; in the mixed solution, the volume ratio of hydrochloric acid to water is 3:2.

[0027] Preferably, in step (7), the N-side electrode is a AuGeNiPtAu electrode, and the alloy is heated at 380° C. for 10 minutes to form an ohmic contact.

[0028] Preferably, in step (8), the thickness of the photoresist is 2.5-3.5 um, the hardening temperature is 80-90° C., and the hardening time is 10-20 min.

[0029] Preferably, in step (10), the method for forming a photoresist having a sidewall microstructure is as follows:

[0030] Since there are dielectric films and reflectors under the GaP of the P-GaP ohmic contact layer, there is a standing wave effect during exposure. During development, 5-10 seconds are added to the normal development time. The development time of the photoresist in the present invention is 65-100 seconds, and the hardening temperature is 80-90°C, which cannot exceed the glass transition temperature of the photoresist, so that a photoresist with a sidewall microstructure is formed; then ICP etching is used to copy the sidewall microstructure on the photoresist to GaP (ICP etching uses photoresist as a mask, and the etching morphology is determined by the mask).

[0031] Anything not described or limited in detail in the above technical solution shall be carried out with reference to the existing technology for manufacturing light emitting diodes.

[0032] The beneficial effects of the present invention are:

[0033] The present invention utilizes the standing wave effect to optimize and adjust the exposure, development time and hardening temperature of the photoresist to form a photoresist with a sidewall microstructure, and then uses the photoresist as a mask to etch GaP using ICP. During the etching process, the sidewall microstructure on the photoresist is copied to GaP. The microstructure reduces the total reflection of the interface and increases the sidewall light emitting area, thereby improving the brightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0035] Figure 1 A schematic diagram of the structure of a light-emitting diode with a sidewall microstructure according to the present invention;

[0036] Figure 2 The side wall morphology after ICP etching using the process of the present invention;

[0037] In the figure, 1. permanent substrate ohmic contact electrode, 2. permanent substrate, 3. reflector, 4. dielectric film, 5. P-type ohmic contact layer, 6. P-GaP ohmic contact layer, 7. P-AlGaInP current spreading layer, 8. P-AlInP confinement layer, 9-MQW multiple quantum well layer, 10. N-AIInP confinement layer, 11. N-AlGaInP current spreading layer, 12. N-AlGaInP roughening layer, 13. N-GaAs ohmic contact layer, 14. N-side electrode. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described, but not limited to this. Anything not fully described in the present invention shall be based on conventional techniques in the art.

[0039] Example 1

[0040] A light emitting diode with a sidewall microstructure comprises, from bottom to top, a permanent substrate ohmic contact electrode 1, a permanent substrate 2, a reflector 3, a dielectric film 4, a P-type ohmic contact layer 5, a P-GaP ohmic contact layer 6, a P-AlGaInP current spreading layer 7, a P-AlInP limiting layer 8, an MQW multi-quantum well layer 9, an N-AlInP limiting layer 10, an N-AlGaInP current spreading layer 11, an N-AlGaInP roughening layer 12, an N-GaAs ohmic contact layer 13 and an N-surface electrode 14, wherein the GaP of the P-GaP ohmic contact layer 6 has a photoresist with a sidewall microstructure.

[0041] The preparation method comprises the following steps:

[0042] (1) using a MOCVD method, an N-GaAs buffer layer, an N-GaInP barrier layer, an N-GaAs ohmic contact layer 13, an N-AlGaInP roughening layer 12, an N-AlGaInP current spreading layer 11, an N-AlInP confinement layer 10, an MQW multi-quantum well layer 9, a P-AlInP confinement layer 8, a P-AlGaInP current spreading layer 7 and a P-GaP ohmic contact layer 6 are sequentially grown on an n-GaAs temporary substrate;

[0043] (2) depositing a SiO2 dielectric film on the P-GaP ohmic contact layer 6 of the epitaxial wafer in step (1), and then performing photolithography, evaporation, etching, and stripping processes to form a P-type ohmic contact layer; the thickness of the SiO2 dielectric film is an odd multiple of 1 / 4 wavelength;

[0044] (3) evaporating a gold reflector on the surface of the wafer obtained in step (2);

[0045] (4) performing Au-Au bonding on the wafer obtained in step (3) and the permanent substrate, with the bonding temperature being 300° C., the bonding time being 45 minutes, and the bonding pressure being 400 kg;

[0046] (5) using a mixed solution of ammonia, hydrogen peroxide and water to remove the n-GaAs temporary substrate of the wafer after bonding, wherein the volume ratio of ammonia, hydrogen peroxide and water in the mixed solution is 1:4:5;

[0047] The N-GaInP barrier layer is removed by using a mixed solution of hydrochloric acid and water; in the mixed solution, the volume ratio of hydrochloric acid to water is 3:2, exposing the N-GaAs ohmic contact layer 13 .

[0048] (6) etching away the N-GaAs ohmic contact layer 13 outside the electrode area;

[0049] (7) evaporating an AuGeNiPtAu electrode on the N-GaAs ohmic contact layer retained in step (6), and alloying at 380° C. for 10 min to form an ohmic contact;

[0050] (8) forming a cutting path pattern on the wafer obtained in step (7) by photolithography, performing a first etching, and then removing the resist;

[0051] (9) roughening the wafer obtained in step (8) on the N-AlGaInP roughening layer;

[0052] (10) Photolithography and ICP etching are used to form a secondary etching pattern on GaP in the cut road. The photoresist thickness is 2.5 μm, the exposure energy is 30 mJ, the development time is 65 seconds, and the hardening temperature is 85° C. to form a photolithography mask with a sidewall microstructure, and then etching is performed to form a photolithography mask with a sidewall microstructure, and then etching is performed;

[0053] (11) thinning the permanent substrate 2, then evaporating the ohmic contact metal TiAu, and alloying at 200° C. for 10 min to form a permanent substrate ohmic contact electrode 1;

[0054] (12) Light-emitting diodes are obtained by laser scribing or diamond knife cutting.

[0055] Comparative Example 1:

[0056] A method for preparing a light emitting diode is a conventional process without sidewall microstructure.

[0057] For the products obtained in Example 1 and Comparative Example 1, 5 products were taken for performance testing, and the results are shown in Table 1:

[0058] Table 1 Performance test results

[0059]

[0060] In Table 1, VF1, LOP1, and WLD1 refer to forward operating voltage, brightness, and wavelength, respectively. Compared with Comparative Example 1, the brightness of Example 1 is improved by 3%.

[0061] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A light emitting diode having a sidewall microstructure, characterized in that: The invention comprises, from bottom to top, a permanent substrate ohmic contact electrode, a permanent substrate, a reflector, a dielectric film, a P-type ohmic contact layer, a P-GaP ohmic contact layer, a P-AlGaInP current spreading layer, a P-AlInP limiting layer, an MQW multi-quantum well layer, an N-AlInP limiting layer, an N-AlGaInP current spreading layer, an N-AlGaInP roughening layer, an N-GaAs ohmic contact layer and an N-side electrode, wherein the GaP of the P-GaP ohmic contact layer has a photoresist with a sidewall microstructure.

2. A method for preparing a light-emitting diode having a sidewall microstructure according to claim 1, characterized in that: The steps include: (1) using a MOCVD method, an N-GaAs buffer layer, an N-GaInP barrier layer, an N-GaAs ohmic contact layer, an N-AlGaInP roughening layer, an N-AlGaInP current spreading layer, an N-AlInP confinement layer, an MQW multi-quantum well layer, a P-AlInP confinement layer, a P-AlGaInP current spreading layer and a P-GaP ohmic contact layer are sequentially grown on an n-GaAs temporary substrate; (2) depositing a dielectric film on the P-GaP ohmic contact layer of step (1), and then performing photolithography, evaporation, etching, and stripping processes to form a P-type ohmic contact layer; (3) evaporating a reflector on the surface of the wafer obtained in step (2); (4) bonding the wafer obtained in step (3) to a permanent substrate; (5) removing the n-GaAs temporary substrate, N-GaAs buffer layer and N-GaInP barrier layer of the wafer after bonding; (6) Etching the N-GaAs ohmic contact layer outside the electrode area; (7) evaporating an N-side electrode on the N-GaAs ohmic contact layer retained in step (6), and forming an ohmic contact through an alloy process; (8) performing photolithography to cut the wafer obtained in step (7) to form a cutting pattern, and after hardening the wafer, using ICP etching to form cutting lines; (9) roughening the wafer obtained in step (8) on the N-AlGaInP roughening layer; (10) using photolithography and ICP etching to form a secondary etching pattern on GaP in the cut road, optimizing and adjusting the exposure and development time and hardening temperature of the photoresist to form a photoresist with a sidewall microstructure; (11) thinning the permanent substrate, and then evaporating an ohmic contact metal and forming an alloy to form an ohmic contact electrode on the permanent substrate; (12) Light-emitting diodes are obtained by laser scribing or diamond knife cutting.

3. The method for preparing a light emitting diode having a sidewall microstructure according to claim 2, characterized in that: In step (2), the dielectric film is a SiO2 dielectric film.

4. The method for preparing a light emitting diode having a sidewall microstructure according to claim 2, characterized in that: In step (3), the reflecting mirror is a gold mirror or a silver mirror.

5. The method for preparing a light emitting diode having a sidewall microstructure according to claim 2, characterized in that: In step (4), the bonding method is Au-Au bonding or Au-In bonding, the bonding temperature is 200-350° C., the pressure is 200-500 kg, and the time is 30-50 min.

6. The method for preparing a light emitting diode having a sidewall microstructure according to claim 2, characterized in that: In step (5), a mixed solution of ammonia water, hydrogen peroxide and water is used to remove the temporary n-GaAs substrate of the wafer after bonding; in the mixed solution, the volume ratio of ammonia water, hydrogen peroxide and water is 1:4:

5.

7. The method for preparing a light emitting diode having a sidewall microstructure according to claim 2, characterized in that: In step (5), the N-GaInP barrier layer is removed by using a mixed solution of hydrochloric acid and water; in the mixed solution, the volume ratio of hydrochloric acid to water is 3:

2.

8. The method for preparing a light emitting diode having a sidewall microstructure according to claim 2, characterized in that: In step (7), the N-side electrode is a AuGeNiPtAu electrode, and the alloy is heated at 380° C. for 10 minutes to form an ohmic contact.

9. The method for preparing a light emitting diode having a sidewall microstructure according to claim 2, characterized in that: In step (8), the thickness of the photoresist is 2.5-3.5 um, the hardening temperature is 80-90° C., and the hardening time is 10-20 min.

10. The method for preparing a light emitting diode having a sidewall microstructure according to claim 2, characterized in that: In step (10), the method for forming a photoresist having a sidewall microstructure is as follows: Since there are dielectric films and reflectors under the GaP of the P-GaP ohmic contact layer, there is a standing wave effect during exposure. During development, the development time of the photoresist is 65-100s, and the hardening temperature is 80-90°C, forming a photoresist with a sidewall microstructure. Then, ICP etching is used to copy the sidewall microstructure on the photoresist to GaP.

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