AlGaN-based ultraviolet light-emitting diode device LED and preparation method thereof

Abstract

The invention discloses an AlGaN-based ultraviolet light-emitting diode device LED (light-emitting diode) and a preparation method thereof. The method provided by the invention comprises the following steps of: realizing ultraviolet LED full-structure epitaxial growth with flat surface and no crack on a GaN / sapphire template through epitaxial processes such as crack presetting and landfill; and then, removing the sapphire substrate by adopting a laser lift-off means, and combining with an ultraviolet LED preparation process to obtain the thin film flip type ultraviolet LED chip. According to the method, the problem that the light extraction efficiency of the ultraviolet LED device is low is solved, the dependence of the ultraviolet LED device on an AlN template is relieved, the production cost is reduced, and the method has important significance on performance improvement and industrial application of the AlGaN-based ultraviolet LED device and is suitable for being vigorously popularized.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of group III nitride semiconductors, and in particular relates to a thin film inverted AlGaN-based ultraviolet light emitting diode structure epitaxy and device preparation. Background Art

[0002] In recent years, AlGaN-based solid-state UV light sources have been widely used in the fields of UV curing, biomedicine, sterilization and disinfection, and are considered to be one of the most promising and valuable directions in the field of III-nitride semiconductors. Compared with gaseous light sources such as mercury lamps, they are environmentally friendly, small in size, low in energy consumption and long in service life, making them an ideal choice to replace traditional UV light sources. However, to date, there are still huge challenges in achieving high-performance AlGaN-based UV light sources, such as UV light-emitting diodes (LEDs), mainly manifested in low wall-to-wall conversion efficiency (WPE).

[0003] The main factor restricting the electro-optical conversion efficiency of UV LEDs is the low light extraction efficiency (LEE), which is mainly reflected in the following: in the flip-chip chip that retains AlN / sapphire, due to the difference in refractive index between AlN, sapphire and air, the escape cone of the emitted light at the sapphire / air interface is limited to 26°, resulting in a device light extraction efficiency of only about 5%. Although the total reflection of the sapphire substrate / air interface can be effectively eliminated by improving the packaging technology and designing the sapphire back light structure, the problem of total reflection of light still exists at the internal AlN / sapphire interface, which seriously restricts the further improvement of light extraction efficiency.

[0004] At present, the preparation of thin-film flip-chip (TFFC) chips by peeling off the substrate is an effective means to completely solve the above-mentioned total reflection problem, which is of great significance to improving the light extraction efficiency and electro-optical conversion efficiency of ultraviolet LEDs. One of the fastest and most effective methods to achieve substrate peeling is the laser lift-off (LLO) technology, which has shown great commercial value and application prospects in InGaN blue LEDs and micro-LEDs.

[0005] In AlGaN-based UV LEDs, laser stripping to remove the substrate has not yet been promoted. On the one hand, short-wavelength, high-power lasers that meet AlN absorption requirements are relatively expensive; on the other hand, and more importantly, during the laser stripping process, the high-hardness Al metal deposition produced by AlN decomposition will cause the epitaxial wafer to break, affecting device preparation. How to use laser stripping to remove the sapphire substrate while ensuring the integrity of the epitaxial wafer and improve the light extraction efficiency of the device is a key issue for the larger-scale promotion and application of AlGaN-based UV LEDs. Summary of the invention

[0006] The purpose of the present invention is to provide a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED and a preparation method thereof, by epitaxially growing a GaN template layer, a pre-crack layer and an AlGaN crack-filling layer on a sapphire substrate as the basis for the epitaxy of the ultraviolet LED structure, it is beneficial to achieve wafer-scale, high-yield, crack-free laser stripping and removal of the sapphire substrate, thereby realizing large-scale preparation of thin film flip-chip ultraviolet LED devices.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED, comprising the following steps:

[0009] S1, epitaxially growing a GaN template on a sapphire substrate to obtain a GaN template layer;

[0010] S2, epitaxially growing a pre-crack layer on the GaN template layer;

[0011] S3, epitaxially growing an AlGaN crack-filling layer on the pre-crack layer;

[0012] S4, epitaxially growing an ultraviolet LED structure on the AlGaN crack buried layer, including an n-AlGaN layer, an active region multi-quantum well layer, a p-AlGaN electron blocking layer, a p-AlGaN layer and a p-GaN layer;

[0013] S5, preparing an n-type electrode on the n-AlGaN layer, and preparing a p-type electrode on the p-GaN layer; depositing an isolation layer between the n-type electrode and the p-type electrode; leading out a metal layer on the n-type electrode, and bonding the metal layer to a substrate;

[0014] S6, peeling off the sapphire substrate;

[0015] S7, removing the GaN template layer and roughening the surface of the pre-crack layer;

[0016] S8, etching the preset crack layer, the AlGaN crack filling layer and the ultraviolet LED structure, leading out the n-type electrode and the p-type electrode, splitting, packaging, and completing the preparation of the thin film flip-chip ultraviolet LED.

[0017] In step S1, the thickness of the GaN template layer is 1-10 μm, preferably 3-6 μm.

[0018] The surface of the GaN template layer has no cracks and has an atomic-level flat surface morphology.

[0019] The GaN template layer is obtained by epitaxial growth through the MOCVD method. During specific implementation, the process parameters can be adjusted according to actual needs, such as a growth temperature of 1040° C., a growth pressure of 300 mbar, and a growth rate of 2 μm / h.

[0020] In step S2, the material of the pre-crack layer is AlN or AlGaN; the molar fraction of the Al component in the pre-crack layer is 30%-100%, preferably 60%-90%, such as 80%. By controlling the molar fraction of the Al component in the pre-crack layer, the pre-crack layer has no absorption of the active area light.

[0021] The thickness of the pre-crack layer is 10-300 nm, preferably 30-150 nm, such as 90 nm.

[0022] The pre-crack layer is obtained by epitaxial growth using a MOCVD method. In specific implementation, the process parameters can be adjusted according to actual needs, such as a growth temperature of 1100° C. and a growth pressure of 100 mbar.

[0023] In step S3, the molar fraction of Al component in the AlGaN crack buried layer is 30%-90%, preferably 50%-80%, such as 65%. By controlling the molar fraction of Al component in the AlGaN crack buried layer, the AlGaN crack buried layer has no absorption for the active area light emission.

[0024] The thickness of the AlGaN crack buried layer is 100-2000 nm, preferably 300-1000 nm, such as 600 nm.

[0025] The AlGaN crack buried layer has no cracks on its surface and has an atomic-level flat step morphology.

[0026] The AlGaN crack filling layer is obtained by epitaxial growth using a MOCVD method. In specific implementation, the process parameters can be adjusted according to actual needs, such as a growth temperature of 1100° C. and a growth pressure of 100 mbar.

[0027] In the step S4 and the step S5, conventional processes in the field of ultraviolet light emitting diode devices can be used to prepare each film layer, and the process parameters can be adjusted according to actual needs.

[0028] In step S4, the molar fraction of the Al component in the n-AlGaN layer is 20-100%, preferably 50-60%; the thickness of the n-AlGaN layer is 0.5-1.5 μm, preferably 1 μm.

[0029] The active region multi-quantum well layer is an AlGaN / AlGaN multi-quantum well structure of several periods, and the light emission wavelength is 210-350nm, preferably 220-310nm.

[0030] In the p-AlGaN electron blocking layer, the molar fraction of the Al component is 20-100%, for example, 60-70%.

[0031] In the p-AlGaN layer, the molar fraction of the Al component is 20-100%, for example, 50-60%.

[0032] The thickness of the p-GaN layer is 1-200 nm, for example, 10-20 nm.

[0033] In step S5, the n-type electrode and the p-type electrode are prepared by photolithography and ICP etching technology.

[0034] Taking the n-type electrode as Ti / Al / Ni / Au as an example, the preparation conditions are: annealing at 800-900°C for 30-40s in N2 atmosphere, preferably at 850°C for 35s. The thicknesses of Ti / Al / Ni / Au are 30nm, 180nm, 50nm, and 100nm respectively.

[0035] Taking the p-type electrode as Ni / Au as an example, the preparation conditions are: annealing at 500-600°C for 250-350s in an O2 atmosphere, preferably at 550°C for 300s; the thickness of the Ni / Au is 10nm and 50nm respectively.

[0036] The thickness of the isolation layer is 700-900 nm, for example, 800 nm.

[0037] In step S6, the stripping of the sapphire substrate is achieved by a laser with a wavelength equal to or shorter than 364 nm, such as a 355 nm Nd:YAG laser (frequency tripling).

[0038] In step S7, the GaN template layer is removed by ICP etching. In specific implementation, the process parameters can be adjusted according to actual needs, for example, etching in a Cl2 / Ar / BCl3 atmosphere for 30 minutes.

[0039] The surface of the pre-crack layer is roughened by wet etching. In specific implementation, the process parameters can be adjusted according to actual needs, such as using KOH solution to etch for 30 seconds.

[0040] In step S8, the etching is implemented by photolithography and ICP technology. During the specific implementation, the process parameter conditions can be adjusted according to actual needs.

[0041] In a second aspect, the present invention provides a thin film flip-chip AlGaN-based ultraviolet light emitting diode device obtained by the preparation method.

[0042] According to an embodiment of the present invention, the thin film flip-chip AlGaN-based ultraviolet light-emitting diode device comprises the following components: a bonding substrate, a metal layer, an isolation layer, an n-type electrode, a p-type electrode, a p-electrode interface, and an ultraviolet LED structure;

[0043] The ultraviolet LED structure is composed of: a preset crack layer, an AlGaN crack filling layer, an n-AlGaN layer, an active region multi-quantum well layer, a p-AlGaN electron blocking layer, a p-AlGaN layer, and a p-GaN layer.

[0044] The design principle of the present invention is as follows:

[0045] The present invention overcomes the limitations of the prior art and innovatively proposes epitaxial growth of a GaN template on a sapphire substrate, which facilitates the peeling of the sapphire substrate by a laser peeling method; and on the basis of the GaN template, a preset crack layer and an AlGaN crack-filling layer are further epitaxially grown to fully release the tensile stress caused by the lattice mismatch between the upper AlGaN and the GaN template, thereby obtaining a high-quality ultraviolet LED epitaxial structure without surface cracks; and then the sapphire substrate is completely peeled off by laser peeling means, and the GaN template layer is removed; and finally, in conjunction with the LED device preparation process, the preparation of a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED is realized.

[0046] The beneficial effects achieved by the present invention are as follows:

[0047] The present invention provides a crack control method to solve the problem of large lattice mismatch (tensile stress) between GaN template and ultraviolet LED structure, which causes surface cracks in epitaxial wafer. The method realizes wafer-scale, high-yield, crack-free laser stripping removal of sapphire substrate, solves the problem of total reflection of light at the internal interface of the wafer, effectively improves the light extraction efficiency of the device, and realizes the large-scale mass production of thin-film flip-chip AlGaN-based ultraviolet LEDs with high yield and high light extraction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the process for preparing thin-film flip-chip AlGaN-based ultraviolet LED devices.

[0049] Figure 2 This is a schematic diagram of the overall structure obtained in steps S1-S4 of the method for preparing a thin-film flip-chip AlGaN-based ultraviolet LED device provided in Example 1.

[0050] Figure 3Schematic diagram of steps S6-S7 in the method for preparing a thin-film flip-chip AlGaN-based ultraviolet LED device provided in Example 1; wherein (a) represents step S6, (b) represents the removal of the GaN template layer in step S7, and (c) represents the surface roughening of the preset crack layer in step S7.

[0051] Wherein: 1 is a sapphire substrate, 2 is a GaN template layer, 3 is a preset crack layer, 4 is an AlGaN crack-filling layer, 5 is an n-AlGaN layer, 6 is an active region multi-quantum well layer, 7 is a p-AlGaN electron blocking layer, 8 is a p-AlGaN layer, 9 is a p-GaN layer, 10 is an n-type electrode, 11 is a p-type electrode, 12 is an isolation layer, 13 is a metal layer, 14 is a bonding substrate, and 15 is a p-electrode interface.

[0052] Figure 4 The light output power comparison results of the thin-film flip-chip AlGaN-based ultraviolet LED chip provided in Example 1 and the comparative example. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0054] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0055] Unless otherwise specified, the reagents, biological materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0056] Example 1: Epitaxy and preparation of 280nm wavelength thin film flip-chip AlGaN-based ultraviolet LED

[0057] like Figure 1 As shown, the epitaxy and preparation method of a thin film flip-chip AlGaN-based ultraviolet LED with a light emission wavelength of 280 nm are as follows:

[0058] S1: epitaxially growing a 5 μm thick GaN template layer 2 on a sapphire substrate 1 by a MOCVD method; the growth conditions are: growth temperature 1040° C., growth pressure 300 mbar, and growth rate 2 μm / h;

[0059] S2: 90nm thick Al is epitaxially grown on the GaN template layer 2 by MOCVD method. 0.8 Ga 0.2 N, as the pre-crack layer 3; the growth conditions are: growth temperature 1100°C, growth pressure 100 mbar;

[0060] S3: epitaxially grow 600nm thick Al on the pre-crack layer 3 by MOCVD method 0.65 Ga 0.35N layer, serving as AlGaN crack filling layer 4; growth conditions: growth temperature 1100°C, growth pressure 100mbar;

[0061] S4: epitaxially growing a UV LED structure on the AlGaN crack buried layer 4 by MOCVD method, such as Figure 2 As shown, the structure includes: 1μm thick n-Al 0.55 Ga 0.45 N layer 5, 5 cycles Al 0.37 Ga 0.63 N(2nm) / Al 0.5 Ga 0.5 N (10nm) multi-quantum well layer 6, 10nm thick p-Al 0.65 Ga 0.35 N electron blocking layer 7, 50nm thick p-Al 0.55 Ga 0.45 N layer 8, 10nm thick p-GaN layer 9; UV LED active region emission wavelength 280nm;

[0062] S5: Ti / Al / Ni / Au electrodes are deposited on the surface of the n-AlGaN layer 5 by photolithography and ICP etching technology, and rapidly annealed in a N2 atmosphere at 850°C for 35s to form an n-type electrode 10; Ni / Au electrodes are deposited on the surface of the p-GaN layer 9, and rapidly annealed in an O2 atmosphere at 550°C for 300s to form a p-type electrode 11; a SiO2 isolation layer 12 is deposited between the n-type electrode and the p-type electrode;

[0063] Through photolithography and ICP etching technology, a 2 μm thick Au metal layer 13 is deposited to lead out the n-type electrode 10, and also serves as a bonding metal layer; through bonding technology, the wafer is bonded to the bonding substrate 14 high n-doped Si sheet;

[0064] The thicknesses of Ti / Al / Ni / Au electrodes are 30nm, 180nm, 50nm, and 100nm, respectively; the preparation process conditions are: temperature 850°C, time 35s;

[0065] The thickness of the Ni / Au electrodes are 10 nm and 50 nm respectively; the preparation process conditions are: temperature of 550° C. and time of 300 s in an O2 atmosphere.

[0066] The thickness of the isolation layer is: 800nm;

[0067] S6: Use 355nm Nd:YAG laser (frequency tripling) to peel off the sapphire substrate 1, such as Figure 3 Middle (a);

[0068] S7: The GaN template layer 2 remaining on the film is removed by ICP etching to expose the surface of the pre-crack layer 3, such as Figure 3 (b); and then roughening the surface of the pre-crack layer 3 by wet etching, such as Figure 3 Medium (c);

[0069] Parameter conditions for removing the GaN template layer: Use ICP etching in a Cl2 / Ar / BCl3 atmosphere for 30 minutes. The specific conditions can be adjusted according to actual conditions.

[0070] Parameter conditions for preset crack layer roughening: use KOH solution to etch for 30s, and the specific conditions can be adjusted according to actual conditions;

[0071] S8: etching downward from the surface of the preset crack layer 3 by photolithography and ICP etching technology to expose the metal of the p-type electrode 11 and lead it out as the p-electrode interface 15; splitting and packaging to obtain a thin film flip-chip AlGaN-based ultraviolet LED chip;

[0072] Etching parameter conditions: Use ICP to etch in Cl2 / Ar / BCl3 atmosphere until the material is completely etched away. The specific conditions can be adjusted according to actual conditions.

[0073] Comparative Example 1: Epitaxy and preparation of 280nm wavelength inverted AlGaN-based ultraviolet LED

[0074] S1: epitaxial growth of 2 μm thick AlN template on sapphire substrate by MOCVD method;

[0075] S2: Epitaxial UV LED structure on AlN / sapphire template, including 1μm thick n-type Al 0.55 Ga 0.45 N layers, 5 cycles of Al 0.37 Ga 0.63 N(2nm) / Al 0.5 Ga 0.5 N (10nm) multi-quantum well structure, 10nm thick p-Al 0.65 Ga 0.35 N electron blocking layer, 50nm thick p-Al 0.55 Ga 0.45 N layer, 10nm thick p-GaN layer; UV LED active region emission wavelength 280nm;

[0076] S3: Ti / Al / Ni / Au electrodes are deposited on the surface of the n-AlGaN layer through photolithography and ICP etching technology, and then rapidly annealed in an N2 atmosphere at 850°C for 35s to form an ohmic contact; Ni / Au electrodes are deposited on the surface of the p-GaN layer, and then rapidly annealed in an O2 atmosphere at 550°C for 300s to form an ohmic contact; and a SiO2 layer is deposited to isolate the n- and p-electrodes; 2μm thick Au metal is deposited through photolithography and ICP etching technology to lead out the n-type and p-type electrodes;

[0077] S4: splitting and packaging to obtain flip-chip AlGaN-based ultraviolet LED chips.

[0078] Effect verification

[0079] The thin film flip-chip AlGaN-based ultraviolet LED structure described in Example 1 and the flip-chip ultraviolet LED structure described in Comparative Example 1 were tested and compared. The results are as follows: Figure 4 As shown:

[0080] At a working current of 100 mA, the light output power of the thin film flip-chip AlGaN-based ultraviolet LED described in Example 1 reaches 31.8 mW, which is much greater than the flip-chip ultraviolet LED described in Comparative Example 1 (17.2 mW).

[0081] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED, comprising the following steps: S1, epitaxially growing a GaN template on a sapphire substrate to obtain a GaN template layer; S2, epitaxially growing a pre-crack layer on the GaN template layer; S3, epitaxially growing an AlGaN crack-filling layer on the pre-crack layer; S4, epitaxially growing an ultraviolet LED structure on the AlGaN crack buried layer, including an n-AlGaN layer, an active region multi-quantum well layer, a p-AlGaN electron blocking layer, a p-AlGaN layer and a p-GaN layer; S5, preparing an n-type electrode on the n-AlGaN layer, and preparing a p-type electrode on the p-GaN layer; depositing an isolation layer between the n-type electrode and the p-type electrode; leading out a metal layer on the n-type electrode, and bonding the metal layer to a substrate; S6, peeling off the sapphire substrate; S7, removing the GaN template layer and roughening the surface of the pre-crack layer; S8, etching the preset crack layer, the AlGaN crack filling layer and the ultraviolet LED structure, and leading out the n-type electrode and the p-type electrode, splitting, and packaging to complete the preparation of the thin film flip-chip ultraviolet LED.

2. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1, characterized in that: In step S1, the surface of the GaN template layer has no cracks and has an atomically smooth surface morphology; The thickness of the GaN template layer is 1-10 μm.

3. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1 or 2, characterized in that: In step S1, the GaN template layer is obtained by epitaxial growth through a MOCVD method.

4. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to any one of claims 1 to 3, characterized in that: In step S2, the material of the pre-crack layer is AlN or AlGaN; In the pre-crack layer, the molar fraction of Al component is 30%-100%; The thickness of the preset crack layer is 10-300nm.

5. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to any one of claims 1 to 4, characterized in that: In step S2, the pre-crack layer is obtained by epitaxial growth using a MOCVD method.

6. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light emitting diode device LED according to any one of claims 1 to 5, characterized in that: In step S3, the molar fraction of Al component in the AlGaN crack buried layer is 30%-90%; The thickness of the AlGaN crack buried layer is 100-2000nm; The AlGaN crack buried layer has no cracks on its surface and has an atomic-level flat step morphology.

7. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to any one of claims 1 to 6, characterized in that: In step S3, the AlGaN crack-filling layer is obtained by epitaxial growth using a MOCVD method.

8. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to any one of claims 1 to 7, characterized in that: In step S6, the stripping of the sapphire substrate is achieved by using a laser with a wavelength equal to or shorter than 364 nm.

9. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light emitting diode device LED according to any one of claims 1 to 8, characterized in that: In step S7, the GaN template layer is removed by ICP etching; The surface of the pre-crack layer is roughened by wet etching.

10. A thin film flip-chip AlGaN-based ultraviolet light emitting diode device LED obtained by the preparation method according to any one of claims 1 to 9.

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