CN109192836B

CN109192836B - Preparation method of LED structure with graded-refractive-index nano structure combined with nano lens

Info

Publication number: CN109192836B
Application number: CN201811142222.1A
Authority: CN
Inventors: 陈湛旭; 万巍; 陈泳竹; 林家勇; 何影记
Original assignee: Guangdong Polytechnic Normal University
Current assignee: ZHONGSHAN ZEDONG LIGHTING Co.,Ltd.
Priority date: 2018-11-09
Filing date: 2018-11-09
Publication date: 2020-03-06
Anticipated expiration: 2038-11-09
Also published as: CN109192836A

Abstract

The invention discloses an LED chip structure with a nano structure combined with a micro lens and a preparation method thereof, which are used for improving the light emitting efficiency of an LED chip. On the prepared LED chip of the transparent diffusion current electrode, the nano structure with the gradually-changed refractive index is prepared, and then the surface micro-lens array structure is prepared. The design principle of the invention is simple, the preparation method is ingenious, Fresnel reflection is reduced by utilizing the medium with the gradually-changed refractive index, and meanwhile, the escape light cone and surface scattering of the LED are increased by utilizing the micro-lens array on the surface, so that the light-emitting efficiency of the LED with the planar structure is further improved.

Description

Preparation method of LED structure with graded-refractive-index nano structure combined with nano lens

Technical Field

The invention relates to a preparation method of a semiconductor electronic component, in particular to a preparation process of an LED structure with a graded-refractive-index nano structure combined with a nano lens.

Background

As a substitute product of the traditional lamp, the solid semiconductor lighting source has a wide development prospect and is known as a new generation light source [ Science 308, 1274-. In recent years, nitride semiconductor devices, particularly Light Emitting Diode (LED) lighting devices, have been significantly developed (the nobel prize in 2014), and have been widely used in the fields of white Light lighting, indicator lamps, signs, color displays, and the like [ Photonics Research 3,184(2015) ]. However, LED is developed to be a high-quality universal light source, which completely replaces other light sources, and the problems of improving light efficiency, reducing cost, reducing chip heat generation, and improving LED service life are also needed to be solved, and all these problems are limited by the lower External Quantum Efficiency (EQE) of LED [ Acta Materialia 61, 945-. The EQE of an LED is determined by Internal Quantum Efficiency (IQE) and extraction efficiency (LEE) and is expressed by Physics Reports 498,189-241 (2011). In recent years, IQE has been greatly improved by improving the structure and growth mode of the active region, and it is reported that the IQE of InGaN/GaN quantum well LEDs can reach 90% or more [ Applied Physics Letters 94,023101(2009) ]. However, since the nitride LED material has a large refractive index difference with air, only a few photons can escape into air, and most other photons are totally reflected at the interface and reabsorbed by the material or form a waveguide mode, so that the LEE of the LED is still low, which limits the application and development of the LED.

Because GaN materials have a high refractive index (n is 2.5), which results in low extraction efficiency of LEDs, a micro-nano technology is used to prepare a related micro-nano structure (or coarsening a surface) to increase a critical angle of light output, which should be the most direct method for improving the light extraction efficiency of LEDs. The outermost layer of a conventional LED chip is a current spreading layer, and an Indium Tin Oxide (ITO) material has been substituted for a conventional nickel-gold material as the current spreading layer of the LED. ITO has a refractive index of about 2, and there are two main losses for light exiting from a high index material to a low index material: the first is that the critical angle of light output is relatively small due to total reflection; the second is fresnel transmission loss. The principle of reducing the loss is to adopt a medium with a gradually-changed refractive index to reduce the Fresnel transmission loss, and design a micro-lens array nano structure to increase the critical angle of light output, so that the light-emitting efficiency of the LED chip is further improved.

Disclosure of Invention

The invention aims to provide a method for preparing an LED structure with a graded-refractive-index nano structure combined with a nano lens. The basic idea is to nano-pattern an ITO transparent electrode on the LED light-emitting surface, melt the residual PS nanospheres at high temperature, prepare single-layer PS nanospheres on the ITO transparent electrode, heat the PS nanospheres at low temperature to form a hemispherical structure, and form a micro-lens array.

The technical scheme of the invention is as follows.

A method for preparing an LED structure with a graded-index nano structure combined with a nano lens comprises the following steps: depositing ITO (about 100-300nm) with a certain thickness on an LED substrate with a planar structure as a transparent electrode, and then carrying out a conventional thick gold electrode preparation process, wherein the conventional thick gold electrode preparation process comprises photoresist coating, first exposure, wet etching of the ITO, ICP etching of a GaN step, photoresist removing and photoresist coating; and carrying out exposure for the second time, plating thick gold and the like, thereby completing the manufacture of the thick gold electrode.

Further comprising the steps of:

s1, the electrode is protected by protecting the thick gold electrode by photolithography, such as by applying a photoresist, exposing, depositing silicon dioxide or metal on the thick gold electrode, and then removing the photoresist. Preparing single-layer closely-arranged Polystyrene (PS) nanospheres on an LED chip with a prepared thick gold electrode, etching the PS nanospheres by using oxygen ions, effectively controlling the diameter of the PS nanospheres, performing ICP (inductively coupled plasma) etching, and etching the surface of the ITO (indium tin oxide) of the transparent electrode to form a periodic nano-column array; the size and height of the ITO nano-pillar array can be effectively controlled by changing the time of oxygen ion etching and ICP etching, so that the sample has better electrical and optical properties. The residual PS nanospheres were retained and could not be removed.

S2, heating the LED chip with the residual PS nanospheres, heating at high temperature to melt the PS nanospheres, so that the PS permeates into the gaps of the nanocolumns, and forming the nanostructure with the gradually-changed refractive index. For example, the temperature can be heated to 140 ℃ or above, and the PS nanospheres can be melted by rotating the chip at a high speed by using a spin coater so as to permeate into the gaps of the nanopillars.

S3, selecting a proper PS nanosphere according to the light-emitting wavelength of the LED chip, and preparing a single-layer PS nanosphere on the surface of the nanostructure with the gradually-changed refractive index. For example, for near UV, blue LEDs, a sphere with a diameter of about 450nm may be selected; for green LEDs, a sphere with a diameter of about 550nm may be chosen; for red LEDs, a small sphere with a period of 650nm may be chosen. And heating the PS nanospheres at a low temperature to enable the nanospheres to form a hemispherical structure on the surface of the medium with the gradually-changed refractive index. For example, the PS nanospheres can be heated at an angle of 80 ° to 100 ° to melt the lower surface of the PS nanospheres away to form a hemispherical structure.

And S4, finally, removing the silicon dioxide or the metal protective layer by acid cleaning, so that the thick gold electrode has no structure, and the transparent electrode ITO layer has a nanostructure with gradually changed refractive index and a hemispherical microlens array structure.

Further, in step S1, a single-layer closely-spaced PS nanosphere array is prepared as a mask on the transparent electrode ITO layer of the LED chip on which the transparent electrode ITO layer and the thick gold electrode have been prepared, and then the nanopillar array is obtained by etching the ITO layer using ICP.

Further, in step S1, the ITO layer of the transparent electrode is prepared into single-layer close-packed nanospheres, and the PS nanospheres are monodisperse polystyrene microspheres, and the diameter of the monodisperse polystyrene microspheres is between 100nm and 2 um.

Further, in step S2, the heating temperature is 120 ° or more.

Further, in step S3, the PS nanospheres are monodisperse polystyrene microspheres, and the diameter of the monodisperse polystyrene microspheres is between 100nm and 2 um.

Further, in step S3, the heating temperature is between 80-100 deg.

By means of the technical scheme, the invention has the advantages that:

1. the method provided by the invention can prepare a novel LED chip which has a medium with gradually-changed refractive index, reduces Fresnel transmission loss of emergent light from a medium with high refractive index to a medium with low refractive index, and has a micro-lens array nano structure to increase the critical angle of light output.

2. The preparation method is ingenious and simple in principle, and is a novel micro-nano structure LED preparation process.

Drawings

FIG. 1 is a flow chart of the preparation method of the present invention.

FIGS. 2(a) to 2(f) are diagrams showing structural changes of an LED during the manufacturing process according to the method of the present invention.

FIG. 2(a) is a schematic diagram of an LED substrate with a transparent ITO layer and a thick gold electrode;

FIG. 2(b) is a schematic diagram of an LED substrate with PS nanospheres added;

FIG. 2(c) is a schematic diagram of the structure in a heated PS nanosphere;

FIG. 2(d) is a schematic diagram of the structure of the nanopillar array etched;

FIG. 2(e) is a schematic structural diagram of the nanopillar gap filled with PS material;

FIG. 2(f) is a schematic diagram of the LED structure after the microlens array is generated;

wherein: 101. a substrate; 102. undoped GaN; 103. n-doping GaN; 104. a multiple quantum well; 105. p-doping GaN; 106. an ITO transparent electrode; 107. p thick metal electrodes; 111. n thick metal electrodes; 110. an ITO nano-pillar structure; 108. polystyrene (PS) nanospheres; 109. a PS film infiltrated into the nano-pillar structure; 112. hemispherical PS nanospheres.

Fig. 3 is a curve table of the ratio of the light intensity of the LED structure prepared by the method to the light intensity of the sample without structure when the graded index is prepared on the surface and the lens array structure is on the surface. Wherein the x-axis is the emission wavelength and the y-axis is the enhancement factor.

Detailed Description

The following describes a method for manufacturing a novel high-efficiency LED structure with reference to the accompanying drawings and examples. The structure of the LED substrate is as follows: a layer of undoped GaN102 is deposited on the substrate 101, followed by a layer of n-doped GaN103, then multiple quantum wells 104, and finally p-doped GaN 105. An ITO transparent electrode 106 with a certain thickness is deposited as a transparent electrode, and then conventional electrode processing is performed, such as photoresist coating, first exposure, wet etching of the ITO transparent electrode 106, ICP etching of GaN steps, photoresist stripping, photoresist coating again, second exposure, plating of p-thick gold 107 and n-thick gold 111, and the like, as shown in fig. 2 (a).

The method comprises the following steps:

the electrodes are protected by first protecting the thick gold electrodes by photolithography, such as by applying a photoresist, exposing, depositing silicon dioxide or metal on the thick gold electrodes, and then removing the photoresist. A single layer of closely packed Polystyrene (PS) nanospheres 108 is distributed on the surface of the LED substrate, as shown in fig. 2 (b); then, the polystyrene PS nanospheres are etched by using oxygen ions, so that the diameters of the polystyrene PS nanospheres can be effectively controlled, as shown in FIG. 2 (c); performing Inductively Coupled Plasma (ICP) etching, so as to etch the ITO transparent electrode 106 of the LED substrate into a periodic ITO nanopillar array 110, as shown in fig. 2 (d); heating the LED chip with the residual polystyrene PS nanospheres 108 to a temperature above 140 °, wherein the polystyrene PS nanospheres 108 will melt to form a PS film 109 infiltrated into the nano-pillar structure, as shown in fig. 2 (e); for a blue LED with a light emitting wavelength of 450nm, a polystyrene PS nanosphere with a diameter of about 450nm is selected, a single-layer polystyrene PS nanosphere is prepared on the surface of the graded-index nanostructure, and the polystyrene PS nanosphere is heated at a low temperature, so that the nanosphere forms a hemispherical PS nanosphere 112 on the surface of the graded-index medium, as shown in fig. 2 (f).

The size and height of the ITO layer nano-pillar array can be effectively controlled by changing the oxygen ion etching time and the ICP etching time, so that the sample has better electrical and optical properties. According to the light emitting wavelength of the LED chip, a proper PS nanosphere is selected, a blue LED chip is designed, the PS nanosphere with the size of 450nm is selected, and a single-layer PS nanosphere is prepared on the surface of the medium with the gradually-changed refractive index, as shown in fig. 2 (f).

Fig. 3 is the ratio of graded index of refraction at the LED surface and the light intensity at the LED surface with a lens array structure to that of a non-structured sample, where the x-axis is the wavelength of the emitted light and the y-axis is the enhancement factor. For example, for a near ultraviolet LED with a light emitting wavelength of 400nm, the enhancement factor of fig. 3 is 1.4, which can effectively improve the light extraction efficiency of the LED.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an LED structure with a graded-index nano structure combined with a nano lens comprises the following steps of preparing an ITO layer of a transparent electrode and an LED substrate of a thick gold electrode, and is characterized in that: also has the following steps:

s1, depositing a silicon dioxide protective layer of dozens of nanometers at the position of a thick gold electrode by utilizing a photoetching method, preparing a single-layer PS nanosphere array on a transparent electrode ITO layer of an LED chip by using Polystyrene (PS) nanospheres, and etching a periodic nanopillar array;

s2, heating the LED chip with the residual PS nanospheres, heating at high temperature to melt the PS nanospheres, so that the PS material permeates into the gaps of the nanocolumns to form a nanostructure with gradually-changed refractive index;

s3, selecting proper PS nanospheres according to the light-emitting wavelength of the LED chip, preparing single-layer PS nanospheres on the surface of the nanostructure with the gradually-changed refractive index, and heating the PS nanospheres at low temperature to enable the nanospheres to form a hemispherical structure on the surface of the nanostructure with the gradually-changed refractive index, wherein a plurality of hemispherical structures form a micro-lens array;

s4, the silicon dioxide protective layer is removed by acid washing so that the thick gold electrode is not covered.

2. The method of claim 1, wherein the graded index nanostructure is combined with a nanolens of the LED structure, and the method comprises: in step S1, a single-layer closely-spaced PS nanosphere array is prepared as a mask on the transparent electrode ITO layer of the LED chip on which the transparent electrode ITO layer and the thick gold electrode have been prepared, and then the nanopillar array is obtained by etching the ITO layer using ICP.

3. The method of claim 2, wherein the graded index nanostructure is combined with a nanolens of the LED structure, and the method comprises: in step S1, the ITO layer of the transparent electrode is prepared into a single layer of closely packed nanospheres, and the PS nanospheres are monodisperse polystyrene microspheres with a diameter of 100nm-2 um.

4. The method of claim 3, wherein the graded index nanostructure is combined with a nanolens of the LED structure, and the method comprises: in step S2, the heating temperature is 120 ° or more.

5. The method of claim 4, wherein the graded index nanostructure is combined with a nanolens of the LED structure, and the method comprises: in step S3, the PS nanospheres are monodisperse polystyrene microspheres, and the diameter of the monodisperse polystyrene microspheres is between 100nm and 2 um.

6. The method of claim 5, wherein the graded index nanostructure is combined with a nanolens of the LED structure, and the method comprises: the heating temperature in step S3 is between 80 ° and 100 °.