Ultraviolet micro-size light emitting diode based on piezoelectronic and preparation method thereof

Abstract

The application discloses a kind of ultraviolet micro light emitting diode based on piezoelectro-optoelectronics and preparation method, the ultraviolet micro light emitting diode includes: substrate layer structure, including: AlN layer, formed on substrate;AlGaN superlattice layer is formed on AlN layer;And N type AlGaN layer, formed on AlGaN superlattice layer;And a plurality of interval arranged microwire structures, each microwire structure includes: AlGaN multi-quantum well microwire layer, formed on N type AlGaN layer;P type AlGaN microwire layer, formed on AlGaN multi-quantum well microwire layer;And P type GaN microwire layer, formed on P type AlGaN microwire layer;Wherein, by applying stress, so that substrate protrudes to the direction of a plurality of interval arranged microwire structures and forms arc structure, in turn, so that layer structure and microwire structure produce bending strain, introduce piezoelectric polarization field.The application as well as the ultraviolet light source micro light emitting diode of piezoelectro-optoelectronics modulation improves the overall light emitting characteristic of ultraviolet micro size light emitting diode.

Description

TECHNICAL FIELD

[0001] At least one embodiment of the present application relates to a light emitting diode and a preparation method, in particular to a piezoelectronic-based ultraviolet micro-size light emitting diode and a preparation method. BACKGROUND

[0002] The ultraviolet light emitting diode (ultraviolet LED) is small in size, friendly to the environment, and long in service life, and has a wide application prospect in various fields such as water purification, medical equipment, full-color display, optical storage, communication, etc.

[0003] The ultraviolet communication in the solar blind band works in a non-line-of-sight manner, has high confidentiality and strong anti-interference ability, and has higher current injection density than the traditional large-size ultraviolet LED, so as to be conducive to obtaining higher modulation bandwidth, and thus the information transmission capacity of the ultraviolet communication can be improved, but the current ultraviolet micro-size LED has problems of low light output power and low photoelectric conversion efficiency. SUMMARY

[0004] Therefore, in order to solve at least one of the above or other problems in the prior art, the present application provides a piezoelectronic-based ultraviolet micro-size light emitting diode and a preparation method, so as to realize higher photoelectric conversion efficiency.

[0005] According to an aspect of the present application, a piezoelectronic-based ultraviolet micro-size light emitting diode is provided, comprising:

[0006] a substrate;

[0007] a layered structure, comprising:

[0008] an AlN layer formed on the substrate;

[0009] an AlGaN superlattice layer formed on the AlN layer; and

[0010] an N-type AlGaN layer formed on the AlGaN superlattice layer; and

[0011] a plurality of spaced microwire structures, each microwire structure comprising:

[0012] an AlGaN multi-quantum well microwire layer formed on the N-type AlGaN layer;

[0013] a P-type AlGaN microwire layer formed on the AlGaN multi-quantum well microwire layer; and

[0014] a P-type GaN microwire layer formed on the P-type AlGaN microwire layer;

[0015] The substrate is protruded to the direction of the plurality of spaced microwire structures by applying stress to form an arc-shaped structure, and the layered structure and the microwire structure are further subjected to bending strain.

[0016] The N-type AlGaN layer is adapted to provide electrons, the P-type AlGaN microwire and the P-type GaN microwire layer are adapted to provide holes, and the electrons and the holes are combined in the AlGaN multi-quantum well layer to generate light.

[0017] According to an embodiment of the present application, the strain amount of the bending strain is less than 1%.

[0018] According to an embodiment of the present application, the direction along which the microwire structure extends is taken as a first direction, in the first direction, the length of the microwire structure is less than the length of the layered structure, and one end of the microwire structure is flush with a first end of the N-type AlGaN layer.

[0019] According to an embodiment of the present application, the ultraviolet micro-size light emitting diode further comprises:

[0020] A P electrode is formed at one end of the microwire structure, and the plurality of P electrodes are interconnected.

[0021] An N electrode is formed at a second end of the N-type AlGaN layer opposite to the first end.

[0022] According to an embodiment of the present application, the ultraviolet micro-size light emitting diode further comprises:

[0023] A passivation material is formed on the sidewall of the microwire structure.

[0024] According to an embodiment of the present application, the size of the layered structure is 60 μm x 60 μm, the size of the microwire structure is 5 μm x 50 μm, and the distance between the plurality of spaced microwire structures is 5 μm.

[0025] According to an embodiment of the present application, the AlGaN superlattice layer comprises first Al component layers and second Al component layers arranged alternately, the Al content in the first Al component layers is 62%-70%, the Al content in the second Al component layers is 55%, and the number of layers of the first Al component layers and the second Al component layers is 15-30.

[0026] According to an embodiment of the present application, the AlGaN multi-quantum well microwire layer comprises AlGaN quantum well microwire layers and AlGaN quantum barrier microwire layers arranged alternately, and the number of the AlGaN quantum well microwire layers is one less than the number of the AlGaN quantum barrier microwire layers.

[0027] According to the embodiment of the present application, the content of Al component in the AlGaN quantum well microwire layer is between 0 and 1, and the content of Al component in the AlGaN quantum barrier microwire layer is less than the content of Al component in the AlGaN quantum well microwire layer.

[0028] According to another aspect of the present application, there is also provided a method for preparing the ultraviolet micro-size light emitting diode as claimed in claims 1-9, comprising:

[0029] forming a layered structure on the substrate by using a method of metal organic chemical vapor deposition or molecular beam epitaxy;

[0030] forming an AlGaN multi-quantum layer, a P-type AlGaN layer and a P-type GaN layer on the layered structure in sequence by using a method of metal organic chemical vapor deposition or molecular beam epitaxy;

[0031] etching the AlGaN multi-quantum well layer, the P-type AlGaN layer and the P-type GaN layer to obtain a plurality of spaced microwire structures;

[0032] extruding the overall structure formed by the substrate, the layered structure and the plurality of spaced microwire structures in a first direction so that the plurality of spaced microwire structures protrude from the substrate and form an arc-shaped structure, and further making the layered structure and the microwire structure produce a bending strain.

[0033] The ultraviolet micro-size light emitting diode provided by the embodiment of the present application protrudes from the substrate to the plurality of spaced microwire structures and forms an arc-shaped structure, stress is applied to the long axis direction of the microwire structure, a bending strain is produced, piezoelectronic effect is generated, the polarization field in the AlGaN multi-quantum well microwire layer can be modulated, and there is no problem of mechanical performance degradation caused by repeated application of strain. The ultraviolet micro-size light emitting diode provided by the embodiment of the present application can reduce the energy band tilt of the AlGaN multi-quantum well microwire layer by using piezoelectronic effect, improve the carrier recombination efficiency of the ultraviolet micro-size light emitting diode, make the in-plane stress introduced by the bending strain reduce the efficiency reduction caused by quantum confinement Stark effect, modulate the piezoelectric polarization field without changing the traditional ultraviolet LED structure, improve the overall photoelectric properties of the ultraviolet micro-size light emitting diode, and expand the research range of such devices. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 A perspective view of the ultraviolet micro-size light emitting diode based on piezoelectronic effect provided by the embodiment of the present application is schematically shown;

[0035] Figure 2The flowchart illustrating the fabrication method of ultraviolet micro-sized light-emitting diodes based on piezoelectric optoelectronics according to an embodiment of the present invention is shown in the figure.

[0036] Figure 3 This schematically illustrates a side cross-sectional view of the complete structure of an ultraviolet LED epitaxially grown on a substrate according to an embodiment of the present invention;

[0037] Figure 4 The illustration schematically shows a side cross-sectional view of an etched N-type mesa provided according to an embodiment of the present invention from a first perspective;

[0038] Figure 5 Schematic illustration Figure 4 Top view;

[0039] Figure 6 The illustration schematically shows a side cross-sectional view of the etching-formed micron-line structure provided according to an embodiment of the present invention from a second perspective;

[0040] Figure 7 Schematic illustration Figure 6 Top view;

[0041] Figure 8 The schematic illustration shows a side cross-sectional view of the formation of N-electrodes and P-electrodes according to an embodiment of the present invention from a first perspective;

[0042] Figure 9 A side view schematically illustrating compression of a chip using a strain application device according to an embodiment of the present invention is shown; and

[0043] Figure 10 Schematic illustration of the use Figure 9 A three-dimensional image of a micro-sized ultraviolet light-emitting diode obtained by compressing a chip using a strain application device.

[0044] Explanation of reference numerals in the attached figures

[0045] 1 substrate

[0046] 2-layer structure

[0047] 21AlN layer

[0048] 22AlGaN superlattice layer

[0049] 23N type AlGaN layer

[0050] 3-micron line structure

[0051] 31AlGaN multi-quantum-well microwire layer

[0052] 32P type AlGaN micron-line layer

[0053] 33P type GaN micron-line layer

[0054] 34AlGaN multiple quantum well layer

[0055] 35P-type AlGaN layer

[0056] 36P-type GaN layer

[0057] 4P electrode

[0058] 5N electrode DETAILED DESCRIPTION

[0059] In the process of realizing the present application, it is found that the piezoelectronic effect is a new technology of coupling the semiconductor characteristics, piezoelectric characteristics and photoelectric characteristics of a material, can introduce a piezoelectric polarization field by external stress, and modulate the generation, separation, transport and recombination of carriers, and is a brand-new research field. The piezoelectric semiconductor material represented by zinc oxide has been widely studied in the fields of sensors, photodetectors, solar cells, light-emitting diodes and the like, but the study of Group III nitride piezoelectric semiconductor materials with wurtzite structure is less, so the application of piezoelectronic effect to the gallium nitride represented nitride material system can provide a new idea for the design of new photoelectric devices.

[0060] Compared with the heterojunction structure, the multiple quantum well has a stronger restriction on the carriers, and the multiple quantum well layer structure is widely used as the active region in various light-emitting diodes, however, due to the strong spontaneous polarization of the nitride material and the piezoelectric polarization at the heterojunction, a strong piezoelectric polarization field is formed in the multiple quantum well, which leads to the decrease of the carrier recombination efficiency, which is called quantum confinement Stark effect (QCSE). However, by applying an in-plane tensile stress to the quantum well, the in-plane compressive stress of the quantum barrier to the quantum well can be compensated, thereby reducing the polarization field in the quantum well and improving the recombination efficiency of the carriers in the quantum well, so that a light-emitting diode with better photoelectric performance is obtained. At the same time, studies have shown that the piezoelectric coefficient of piezoelectric materials under micro-nano structure will be much larger than that under large size structure, so it is more conducive to realize the modulation of carrier recombination by introducing piezoelectronic effect in the ultraviolet micro-size light-emitting diode, which has important significance for improving the photoelectric properties of the ultraviolet micro-size light-emitting diode.

[0061] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with specific embodiments and with reference to the drawings.

[0062] Figure 1 A perspective view of the ultraviolet micro-size light-emitting diode based on piezoelectronic effect provided by the embodiment of the present application is schematically shown.

[0063] As Figure 1As shown, the piezoelectro-optoelectronic based ultraviolet micro-size light emitting diode comprises a substrate 1, a layered structure 2 and a plurality of spaced apart micron wire structures 3.

[0064] The layered structure 2 comprises an AlN layer 21, an AlGaN superlattice layer 22 and an N-type AlGaN layer 23. The AlN layer 21 is formed on the substrate, the AlGaN superlattice layer 22 is formed on the AlN layer, and the N-type AlGaN layer 23 is formed on the AlGaN superlattice layer 22.

[0065] Each of the micron wire structures 3 comprises an AlGaN multi-quantum well micron wire layer 31, a P-type AlGaN micron wire layer 32 and a P-type GaN micron wire layer 33. The AlGaN multi-quantum well micron wire layer 31 is formed on the N-type AlGaN layer, the P-type AlGaN micron wire layer 32 is formed on the AlGaN multi-quantum well micron wire layer, and the P-type GaN micron wire layer 33 is formed on the P-type AlGaN micron wire layer.

[0066] The substrate 1 is convex to the plurality of spaced apart micron wire structures 3 and forms an arc-shaped structure, so that the layered structure 2 and the micron wire structures 3 generate a bending strain. The N-type AlGaN layer 23 is adapted to provide electrons, the P-type AlGaN micron wire layer 32 and the P-type GaN micron wire layer 33 are adapted to provide holes, and the electrons and the holes recombine in the AlGaN multi-quantum well layer to generate light.

[0067] According to an embodiment of the present application, the strain amount of the bending strain is less than 1%, and preferably 0.1%-0.5%. If the strain amount of the bending strain is too large, it will be over-compensated.

[0068] According to an embodiment of the present application, a direction along which the micron wire structure 3 extends is taken as a first direction, a length of the micron wire structure 3 along the first direction is less than a length of the layered structure along the first direction, and one end of the micron wire structure 3 is flush with a first end of the N-type AlGaN layer 23.

[0069] According to an embodiment of the present application, the ultraviolet micro-size light emitting diode further comprises P electrodes 4 and an N electrode 5. The P electrodes 4 are formed at one end of the micron wire structure 3, and the P electrodes 4 are interconnected. The N electrode 5 is formed at a second end of the N-type AlGaN layer 23 opposite to the first end.

[0070] According to an embodiment of the present application, the ultraviolet micro-size light emitting diode further comprises a passivation material formed on sidewalls of the micron wire structure 3.

[0071] According to an embodiment of the present application, the layered structure 2 has a size of 60μm×60μm, the micron wire structure 3 has a size of 5μm×50μm, and the distance between the plurality of spaced apart micron wire structures 3 is 5μm.

[0072] According to an embodiment of the present application, the AlGaN superlattice layer 22 comprises first Al component layers and second Al component layers arranged alternately, the Al content in the first Al component layers is 62%-70%, the Al content in the second Al component layers is 55%, and the number of layers of the first Al component layers and the second Al component layers is 15-30.

[0073] According to an embodiment of the present application, the AlGaN multi-quantum well microwire 31 is an alloy of GaN and AlN, both of which have high piezoelectric coefficients. The AlGaN multi-quantum well microwire 31 comprises AlGaN quantum well microwire layers and AlGaN quantum barrier microwire layers arranged alternately, wherein the number of the AlGaN quantum well microwire layers is one less than the number of the AlGaN quantum barrier microwire layers.

[0074] According to an embodiment of the present application, the Al content in the AlGaN quantum well microwire layers is between 0 and 1, and the Al content in the AlGaN quantum barrier microwire layers is less than the Al content in the AlGaN quantum well microwire layers.

[0075] According to an embodiment of the present application, a preparation method of an ultraviolet micro-size light emitting diode is also provided, which is suitable for preparing the ultraviolet micro-size light emitting diode as described above, and comprises the following steps.

[0076] forming a layered structure 2 on the substrate 1 by means of metal organic chemical vapor deposition or molecular beam epitaxy;

[0077] forming an AlGaN multi-quantum layer, a P-type AlGaN layer and a P-type GaN layer on the layered structure 2 in sequence by means of metal organic chemical vapor deposition or molecular beam epitaxy;

[0078] etching the AlGaN multi-quantum well layer, the P-type AlGaN layer and the P-type GaN layer to obtain a plurality of spaced microwire structures 3;

[0079] extruding the overall structure formed by the substrate 1, the layered structure 2 and the plurality of spaced microwire structures 3 in a first direction so that the plurality of spaced microwire structures 3 protrude from the substrate and form an arc-shaped structure, and further so that the layered structure 2 and the microwire structures 3 produce bending strain.

[0080] According to an embodiment of the present application, the bending strain introduced by compression is at least 10 μm.

[0081] According to an embodiment of the present application, a preparation method of an ultraviolet micro-size light emitting diode is provided, as shown in Figure 2 and specifically comprising the following steps:

[0082] Step 1: as shown inFigure 3 As shown, a complete ultraviolet LED structure is epitaxially grown on a sapphire substrate using MOCVD / MBE. The complete ultraviolet LED structure includes: an AlN layer 21, an AlGaN superlattice layer 22, an N-type AlGaN layer 23, an AlGaN multi-quantum-well layer 34, a P-type AlGaN layer 35, and a P-type GaN layer 36.

[0083] The AlN layer 21 has a thickness of 0.9 μm-1 μm. In the AlGaN superlattice layer 22, the high-Al composition layer (first Al composition layer) has an Al content of 62%-70%, and the low-Al composition layer (second Al composition layer) has an Al content of 55%. The first and second Al composition layers are grown alternately for 15-30 cycles. The N-type AlGaN layer 23 has a thickness of 2-3 μm and an Al composition of 55%. The AlGaN multi-quantum-well layer 34 has 5 cycles. The Al compositions of the AlGaN quantum barrier layer and the AlGaN quantum wells are 50% and 35%, respectively. The emission bands of deep ultraviolet, far ultraviolet, and near ultraviolet can be selected by changing the Al composition of the quantum wells. The Al composition of the P-type AlGaN layer 35 is set to about 60%, and the total thickness is 100-150 nm. The thickness of the P-type GaN layer 36 is 166 nm.

[0084] Step 2: Thin the substrate 1 to 60-100μm, or transfer the entire structure of the UV LED to a PET or PEN flexible substrate.

[0085] Step 3: Use a photoresist mask and ICP to etch the entire structure of substrate 1 and UV LED, resulting in a square structure with a cross-sectional dimension of 60μm×60μm.

[0086] Specifically, such as Figure 4 As shown, using photoresist as a mask, an AlGaN multi-quantum-well layer 34, a P-type AlGaN layer 35, and a P-type GaN layer 36 were etched by ICP on one side of a square structure with a cross-section of 60 μm × 60 μm to obtain a 10 μm × 60 μm N-type mesa. Its top view is shown below. Figure 5 As shown

[0087] Step 4: As Figure 6 As shown, the AlGaN multi-quantum-well layer 34, the P-type AlGaN layer 35, and the P-type GaN layer 36 are further etched to expose the N-type AlGaN layer 23, resulting in a multi-spaced micrometer line structure 3 with dimensions of 5 μm × 50 μm. The sidewalls of the multi-spaced micrometer line structure 3 are then passivated. Its top view is shown below. Figure 7 As shown.

[0088] Passivation materials can be SiO2 or Al2O3.

[0089] Step 5: preparation of N electrode and P electrode, and realization of interconnection of P electrode, structure as shown in Figure 8

[0090] In preparation of N electrode 4 and P electrode 5, in order to reduce the strain introduced by thermal stress of evaporated metal to epitaxial layer, influence of application of mechanical stress, it is considered to prepare N electrode 4 and P electrode 5 at both ends of microwire, the width of P electrode 5 is 5 μm, and the electrode material can be selected from conductive materials such as nickel (Ni) / gold (Au), ITO, etc. Six microwire structures 3 simultaneously emit light under external current injection.

[0091] Step 6: using stress application device to make substrate 1 protrude towards multiple spaced microwire structures 3 and form arc-shaped structure to generate bending strain.

[0092] The devices prepared in steps 1-5 are encapsulated on a chip, wherein the multiple devices form an array structure, as shown in Figure 9 The chip is placed in the strain application device along the long axis direction of the microwire structure 3, and the compression amount of the chip along the long axis direction of the microwire is controlled by a precision micrometer. As shown in Figure 10 , the ultraviolet micro-size light emitting diode located at the deformation symmetry axis bears in-plane tensile stress, which introduces vertical in-plane compressive stress in the quantum well, thereby realizing photoelectric modulation. The displacement accuracy provided by the precision micrometer is 5 μm, and the strain amount applied on a single microwire by the bending strain of the entire chip is smaller, so that precise control of the strain amount can be realized.

[0093] The ultraviolet micro-size light emitting diode provided by the embodiment of the present application modulates the polarization field in the AlGaN multi-quantum well microwire layer 31 by constant strain, and there is no problem of mechanical performance degradation caused by repeated application of strain, reduces the band tilt in the quantum well by using piezoelectronic effect, improves the carrier recombination efficiency of the ultraviolet AlGaN-based micro-size light emitting diode, modulates the piezoelectric polarization field without changing the traditional structure of the ultraviolet LED, and expands the research range of such devices.

[0094] The ultraviolet micro-LED with introduced piezoelectronic effect according to the embodiment of the present application can obtain better photoelectric performance, effectively improve the ultraviolet communication bandwidth, and realize preparation of high-performance ultraviolet micro-LED devices.

[0095] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above-described specific embodiments are only for the specific embodiments of the present application and are not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.​

Claims

1. An ultraviolet micro-size light emitting diode based on piezoelectronic optoelectronics, comprising: a substrate; a layered structure, comprising: an AlN layer formed on the substrate; an AlGaN superlattice layer formed on the AlN layer; and an N-type AlGaN layer formed on the AlGaN superlattice layer; and a plurality of spaced-apart microwire structures, each of the microwire structures comprising: an AlGaN multi-quantum well microwire layer formed on the N-type AlGaN layer; a P-type AlGaN microwire layer formed on the AlGaN multi-quantum well microwire layer; and a P-type GaN microwire layer formed on the P-type AlGaN microwire layer; wherein, by applying stress, the substrate is caused to protrude in the direction of the plurality of spaced-apart microwire structures and form an arc-shaped structure, and further cause the layered structure and the microwire structures to produce a bending strain; wherein, the N-type AlGaN layer is adapted to provide electrons, the P-type AlGaN microwire and the P-type GaN microwire layer are adapted to provide holes, and the electrons and the holes recombine in the AlGaN multi-quantum well microwire layer, and further emit light; an amount of the bending strain is less than 1%; a direction along which the microwire structure extends is taken as a first direction, in the first direction, a length of the microwire structure is less than a length of the layered structure, and one end of the microwire structure is flush with a first end of the N-type AlGaN layer.

2. The ultraviolet micro-size light emitting diode of claim 1, further comprising: a P electrode formed on one end of the microwire structure, and a plurality of P electrodes are interconnected between them; an N electrode formed on a second end of the N-type AlGaN layer opposite to the first end.

3. The ultraviolet micro-size light emitting diode of claim 1, further comprising: a passivation material formed on a sidewall of the microwire structure.

4. The ultraviolet micro-sized light emitting diode of claim 1, wherein, a size of the layered structure is 60 μm x 60 μm, a size of the microwire structure is 5 μm x 50 μm, and a distance between the plurality of spaced-apart microwire structures is 5 μm.

5. The ultraviolet micro-sized light emitting diode of claim 1, wherein, the AlGaN superlattice layer comprises first Al component layers and second Al component layers arranged alternately, an Al content in the first Al component layers is 62%-70%, an Al content in the second Al component layers is 55%, and a number of layers of the first Al component layers and the second Al component layers is 15-30.

6. The ultraviolet micro-sized light emitting diode of claim 1, wherein, the AlGaN multi-quantum well microwire layer comprises AlGaN quantum well microwire layers and AlGaN quantum barrier microwire layers arranged alternately, and a number of the AlGaN quantum well microwire layers is one less than a number of the AlGaN quantum barrier microwire layers.

7. The ultraviolet micro-sized light emitting diode of claim 6, wherein, an Al component content in the AlGaN quantum well microwire layers is between 0 and 1, and an Al component content in the AlGaN quantum barrier microwire layers is less than the Al component content in the AlGaN quantum well microwire layers.

8. A method for preparing a piezoelectronic ultraviolet micro-size light emitting diode, suitable for preparing the piezoelectronic ultraviolet micro-size light emitting diode according to any one of claims 1-7, comprising: forming a layered structure on a substrate by metal organic chemical vapor deposition or molecular beam epitaxy; forming an AlGaN multi-quantum layer, a P-type AlGaN layer and a P-type GaN layer on the layered structure in sequence by metal organic chemical vapor deposition or molecular beam epitaxy; etching the AlGaN multi-quantum well layer, the P-type AlGaN layer and the P-type GaN layer to obtain a plurality of spaced micro-wire structures; extruding the whole structure formed by the substrate, the layered structure and the plurality of spaced micro-wire structures in a first direction, so that the plurality of spaced micro-wire structures protrude from the substrate and form an arc-shaped structure, and further make the layered structure and the micro-wire structure produce a bending strain.

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