CN104659180A - Transparent electrode structure of GaN-based LED (Light Emitting Diode) with high light extraction efficiency and preparation method thereof - Google Patents

Abstract

The invention relates to a transparent electrode structure and a preparation method thereof, particularly relates to a transparent electrode structure of a GaN-based LED (Light Emitting Diode) with high light extraction efficiency and a preparation method thereof and belongs to the technical field of LED semiconductor devices. According to the technical scheme provided by the invention, the transparent electrode structure comprises a GaN substrate, wherein the GaN substrate is provided with a nano column layer and an ITO (Indium Tin Oxide) layer covering the nano column layer; the nano column layer comprises a plurality of nano columns; the ITO layer covers on the nano columns and column disconnecting holes at the two sides of the nano columns are filled with the ITO layer, so that the ITO layer and the GaN substrate are contacted. The transparent electrode structure has the advantages that the light extraction efficiency of the GaN-based positive LED can be obviously improved, the process operation is convenient, the cost is low, the application range is wide, and the safe and reliable effects are achieved.

Description

High light extraction efficiency GaN-based LED transparent electrode structure and preparation method

technical field

The invention relates to a transparent electrode structure and a preparation method, in particular to a high light extraction efficiency GaN-based LED transparent electrode structure and a preparation method, belonging to the technical field of LED semiconductor devices.

Background technique

The popularity of solid-state lighting applications in the future depends on the development of high-efficiency GaN-based LED preparation technology. One of the fundamental obstacles restricting the performance improvement of GaN-based front-mount LEDs is the high refractive index (relative to the external medium) of its constituent materials. Due to the significant difference in the refractive index between the GaN-based material (n=2.3) and the air medium (n=1), the light escape cone angle of the GaN-based front-mount LED is relatively small, and most of the light is difficult to exit from the device and be lost. the light extraction efficiency of the device. Therefore, a lot of research work has been devoted to how to improve the light extraction efficiency of the device, such as ITO surface roughening, graded index layer, patterned sapphire substrate, hot acid sidewall etching, omnidirectional mirror, Photonic crystals, device geometry optimization and other methods.

Generally speaking, since GaN-based front-mount LEDs account for the largest proportion of light emitted from the top surface, changing the top surface morphology of the device to increase the probability of light emission is one of the effective ways to improve device efficiency. It has been reported that using natural lithographic patterning technology to roughen the ITO transparent electrode layer; adjusting the MOCVD epitaxial growth conditions to form p-GaN surface micropits; What is more, there are also obvious shortcomings and deficiencies in the above-mentioned method itself. ITO roughening usually requires dry etching, which usually causes the deterioration of the electrical properties of ITO; epitaxial roughening of the p-GaN surface will sacrifice growth quality and doping efficiency to a certain extent; chemical growth of ZnO nanocolumns is complicated, and nanocolumns Adhesion is also difficult to guarantee. So far, the preparation methods with good comprehensive effect and simple operation are rarely mentioned. Therefore, there is an urgent need to develop a new method that can significantly improve the light extraction efficiency without negatively affecting other device characteristics and has better production feasibility.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a GaN-based LED transparent electrode structure and preparation method with high light extraction efficiency, which can significantly improve the light extraction efficiency of GaN-based formal LEDs, with convenient process operation and low cost. Wide adaptability, safe and reliable.

According to the technical solution provided by the present invention, the high light extraction efficiency GaN-based LED transparent electrode structure includes a GaN substrate; a nano-column layer is arranged on the GaN substrate and an ITO layer covering the nano-column layer; the nano-column The layer includes several nano-columns, and the ITO layer covers the nano-columns and fills the column isolation holes on both sides of the nano-columns, so that the ITO layer is in ohmic contact with the GaN substrate.

The nano-column is a silicon nitride nano-column, and the height and diameter of the nano-column are between 1/4λ˜λ, where λ is the wavelength of light emitted by the GaN-based LED.

A method for preparing a GaN-based LED transparent electrode structure with high light extraction efficiency, the method for preparing the transparent electrode structure includes the following steps:

a. Providing a GaN substrate, and disposing a nanobody layer on the GaN substrate;

b. setting an etching mask layer on the nanobody layer, and the etching mask layer covers the nanobody layer;

c. setting a nano-thin layer on the etching mask layer;

d, annealing the nano-thin layer to agglomerate a number of nano-dots densely arranged on the etching mask layer, and form nano-dot holes outside the nano-dots;

e. Using the nano-dots as a mask, dry-etching the etching mask layer and the nanobody layer to remove the etching mask layer corresponding to the position of the nano-dot hole and the underside of the etching mask layer part of the nanobody layer to obtain an etch mask block located under the nanodots;

f. removing the above-mentioned nano-dots, and performing wet etching on the nanobody layer by using the etching mask block, so as to remove the nanobody layer outside the etching mask block;

g, removing the above-mentioned etching mask block to obtain a number of disconnected nanocolumns;

h. Depositing an ITO layer on the above-mentioned nanocolumns, and annealing the ITO layer, so that the ITO layer is in ohmic contact with the GaN substrate.

The GaN substrate is a P-GaN substrate, and the nanobody layer is a silicon nitride layer deposited on the GaN substrate by PECVD.

The etching mask layer is a silicon dioxide layer deposited on the nanocolumn layer by PECVD.

The nano-thin layer is an Ag layer evaporated by electron beam or magnetron sputtering. The temperature range of the annealing of the nano-thin layer to form nano-dots is 450°C-550°C.

The diameter of the nano-dot is 200nm-500nm. The annealing temperature for annealing the ITO layer so that the ITO layer is in ohmic contact with the GaN substrate is 450° C.-650° C.

The nano-column is a silicon nitride nano-column, and the height and diameter of the nano-column are between 1/4λ˜λ, where λ is the wavelength of light emitted by the GaN-based LED.

The present invention has the following advantages:

1. The transparent electrode structure is composed of submicron-scale nano-column structure on the GaN substrate and the ITO layer covering it. It does not need to change the surface morphology of the GaN substrate, and there is no risk of damage to the GaN substrate. In the GaN-based LED light-emitting wavelength range, the refractive index of the Si ₃ N ₄ nanocolumn is basically the same as that of the ITO layer, which is close to the refractive index of the GaN substrate, which can effectively avoid the Fresnel reflection loss between the optical microstructure and the LED device.

2. High-density Si ₃ N ₄ optical microstructures are obtained by using natural photolithographic patterning technology, which has low production cost, easy control of pattern size, concentrated distribution, and high repeatability. Combined with the precise control of the deposition thickness of Si ₃ N ₄ by PEVCD, the light extraction optimization of the geometric size of the optical microstructure is realized, and the emission probability of the internal light emitted by the GaN-based LED is maximized.

3. Using the non-destructive pattern transfer method of dry etching first and then wet etching, with the help of dry etching's excellent vertical transfer and rate control characteristics, the submicron-scale natural photolithography pattern is transferred to the etching mask layer, and removed Most of the nanobody layer in the pattern area, and finally the remaining nanobody layer is completely removed by selective wet etching between SiO ₂ and Si ₃ N ₄ to obtain nanopillars, which fundamentally avoids surface damage to the p-GaN substrate , will not affect the electrical characteristics of the LED.

Description of drawings

FIG. 1 is a schematic diagram of a conventional transparent electrode structure.

Fig. 2 is a schematic diagram of the transparent electrode structure of the present invention.

Figures 3 to 13 are cross-sectional views of specific implementation process steps for preparing a transparent click structure in the present invention, wherein

Fig. 3 is a cross-sectional view of the GaN substrate of the present invention.

FIG. 4 is a cross-sectional view of a nanobody layer obtained on a GaN substrate according to the present invention.

Fig. 5 is a cross-sectional view of the present invention after obtaining an etching mask layer on the nanobody layer.

FIG. 6 is a cross-sectional view of the present invention after obtaining a nano-thin layer on the etching mask layer.

Fig. 7 is a cross-sectional view of nano dots obtained by annealing the nano thin layer according to the present invention.

FIG. 8 is a cross-sectional view of an etching mask block obtained by etching using nano dots as a mask according to the present invention.

Fig. 9 is a cross-sectional view of the present invention after nano-dots are removed.

FIG. 10 is a cross-sectional view of the nanobody layer etched by using an etching mask block according to the present invention.

Fig. 11 is a cross-sectional view of nanocolumns obtained in the present invention.

Fig. 12 is a cross-sectional view of the present invention after an ITO layer is disposed on the nanocolumn.

13 is a cross-sectional view of the present invention after the ITO layer is annealed so that the ITO layer is in ohmic contact with the GaN substrate.

Explanation of reference numerals: 1-GaN substrate, 2-nanocolumn, 3-column isolation hole, 4-ITO layer, 5-nanometer body layer, 6-etching mask layer, 7-nanometer thin layer, 8-nanometer point , 9-nano dot hole, 10-first etching hole, 11-second etching hole, 12-etching mask block and 20-ITO flat layer.

Detailed ways

The present invention will be further described below in conjunction with specific drawings and embodiments.

As shown in Fig. 1: it is the schematic diagram of existing LED transparent electrode structure, specifically is to arrange ITO flat layer 20 on GaN substrate 1, and ITO flat layer 20 is in ohmic contact with GaN substrate 1, and the transparent electrode structure of this kind of structure has lower light extraction efficiency.

As shown in Figure 2, in order to obtain high light extraction efficiency, the present invention comprises GaN substrate 1; On described GaN substrate 1, arrange nanocolumn layer and cover the ITO layer 4 on described nanocolumn layer; Described nanocolumn layer comprises several The nano-column 2 , the ITO layer 4 covers the nano-column 2 and fills the column isolation holes 3 on both sides of the nano-column 2 , so that the ITO layer 4 is in ohmic contact with the GaN substrate 1 .

Specifically, the nanocolumn 2 is a silicon nitride nanocolumn, and within the GaN-based LED light-emitting wavelength range, the refractive index of the silicon nitride nanocolumn 2 is basically the same as that of the ITO layer 4, and is close to the refractive index of the GaN substrate 1. The nano-column 2 protrudes on the GaN substrate 1, and the nano-column 2 on the GaN substrate 1 is not connected to each other, that is, the column isolation hole 3 penetrates the nano-column 2 and can form all the nano-columns 2 into a shape that is not connected to each other. , using the geometric shape of the nano-column 2 can increase the probability of emitting light in the GaN-based LED, and can effectively avoid the Fresnel reflection loss between the optical microstructure and the LED device, that is, to achieve the purpose of obtaining high light extraction efficiency.

Generally, the height and diameter of the nanocolumn 2 are between 1/4λ∼λ, where λ is the light wavelength of the GaN-based LED. After the height and diameter of the nanocolumn 2 are matched with the light wavelength, the maximum light output can be further ensured. change.

As shown in Figures 3 to 13, the above GaN-based LED transparent electrode structure with high light extraction efficiency can be prepared through the following process steps, and the specific steps include:

a, providing a GaN substrate 1, and disposing a nanobody layer 5 on the GaN substrate 1;

As shown in FIGS. 3 and 4 , the GaN substrate 1 is a P-GaN substrate, and the nanobody layer 5 is a silicon nitride layer deposited on the GaN substrate 1 by PECVD. The thickness of the nanobody layer 5 is between 1/4 and 1 time of the light emission wavelength of the GaN-based LED. Generally, the wavelength range of the GaN-based LED is 400nm-600nm, that is, the thickness of the nanobody layer 5 is 100-600nm.

b. setting an etching mask layer 6 on the nanobody layer 5, and the etching mask layer 6 covers the nanobody layer 5;

As shown in FIG. 5 , the etching mask layer 6 is a silicon dioxide layer deposited on the nanocolumn layer 5 by PECVD. Generally, the thickness of the etching mask layer 6 is more than 1/4 of the thickness of the nano-column layer 5 .

c. setting a nano-thin layer 7 on the etching mask layer 6;

As shown in FIG. 6 , the nano-thin layer 7 is an Ag layer by electron beam evaporation or magnetron sputtering.

d, annealing the nano-thin layer 7 to agglomerate a plurality of nano-dots 8 densely arranged on the etching mask layer 6, and form nano-dot holes 9 outside the nano-dots 8;

As shown in FIG. 7 , the annealing temperature range of the nano-thin layer 7 to form the nano-dots 8 is 450° C.-550° C., and the annealing method is rapid annealing (RTA). The thickness of the nano-thin layer 7 is related to the diameter of the nano-dot 8, and the diameter of the nano-dot 8 is 200nm-500nm. After the nano-dots 8 are formed by annealing, a natural photolithography pattern can be obtained on the etching mask layer 6 . After the nano-thin layers 7 are aggregated to form nano-dots 8 , nano-dot holes 9 are obtained outside the nano-dots 8 , and the etching mask layer 6 can be partially exposed through the nano-dot holes 9 . The specific process of annealing the Ag nano-thin layer 7 to agglomerate to form nano-dots 8 is well known to those skilled in the art, and will not be described in detail here.

e. Using the nano-dots 8 as a mask, dry-etch the etching mask layer 6 and the nanobody layer 5 to remove the etching mask layer 6 corresponding to the position of the nano-dot hole 9 and the etching Part of the nanobody layer 5 below the mask layer 6, so as to obtain an etching mask block 12 located below the nanodot 8;

As shown in Figure 8, since the nano-dot hole 9 can partially expose the etching mask layer 6, after using the nano-dot 8 as a blocking mask, the exposed etching mask layer 6 and the exposed etching mask layer 6 can be removed by dry etching. The nanobody layer 5 below the mask layer 6 is etched, and the thickness of the remaining nanobody layer 5 can be selected according to process conditions such as etching time. Because the etching mask layer 6 of the exposed part is etched away, therefore, the etching mask layer 6 below the nano-dot 8 and in contact with the nano-dot 8 will form an etching mask block 12, and at the same time, The outer sides of the nano dots 8 and the etching mask block 12 form a first etching hole 10 through which the corresponding part of the nanobody layer 5 can be exposed.

f. Remove the above-mentioned nano-dots 8, and use the etching mask block 12 to wet-etch the nano-body layer 5, to remove the nano-body layer 5 outside the etching mask block 12;

As shown in Figures 9 and 10, after removing the nano-dots 8, the surface of the etching mask block 12 is exposed, and using the etching mask block 12 as a mask, the nano-body layer 5 of the above-mentioned exposed part is etched by a wet method, The nanobody layer 5 below the bottom of the first etching hole 10 is removed by etching to obtain a second etching hole 11 through which the surface of the GaN substrate 1 can be exposed. Generally, dilute nitric acid can be used to remove the nano-dots 8 , and heated dilute phosphoric acid can be used to wet-etch the nano-body layer 5 . The specific process and conditions are well known to those skilled in the art and will not be repeated here.

g, removing the above-mentioned etching mask block 12 to obtain a number of nano-pillars 2 that are not connected to each other;

As shown in FIG. 11, since the nanobody layer 5 on the outside of the etching mask block 12 is removed by wet etching, the nanobody layer 5 directly below the etching mask block 12 can be obtained, thereby obtaining several nanocolumns 2, The nanopillars 2 are not connected to each other through the column isolation holes 3 . The height of the nanopillar 2 is consistent with the thickness of the nanobody layer 5 . A BOE solution may be used for etching the mask block 12 , and the specific removal process is well known to those skilled in the art.

h. Depositing an ITO layer 4 on the nanocolumn 2 and annealing the ITO layer 4 so that the ITO layer 4 is in ohmic contact with the GaN substrate 1 .

As shown in Figures 12 and 13, the annealing temperature for annealing the ITO layer 4 so that the ITO layer 4 is in ohmic contact with the GaN substrate 1 is 450°C-650°C, and the deposition method of the ITO layer 4 can be electron beam evaporation, reactive plasma deposition or magnetron sputtering; the annealing method of the ITO layer 4 is furnace tube annealing or rapid annealing. The specific process of annealing the ITO layer 4 to make the ohmic contact between the ITO layer 4 and the GaN substrate 1 is well known to those skilled in the art and will not be repeated here.

The transparent electrode structure of the present invention is composed of submicron scale nano-columns 2 on the GaN substrate 1 and the ITO layer 4 covering it, without changing the surface morphology of the GaN substrate 1 and without the risk of damage to the GaN substrate 1 . Within the GaN-based LED light-emitting wavelength range, the refractive index of the nanocolumn 2 using Si ₃ N ₄ is basically the same as that of the ITO layer 4, which is close to the refractive index of the GaN substrate 1, which can effectively avoid the Fresnel between the optical microstructure and the LED device. reflection loss.

The high-density Si ₃ N ₄ optical microstructure is obtained by using the natural photolithographic patterning technology, the production cost is low, the pattern size is easy to control, the distribution is concentrated, and the repeatability is high. Combined with the precise control of the deposition thickness of Si ₃ N ₄ by PEVCD, the light extraction optimization of the geometric size of the optical microstructure is realized, and the emission probability of the internal light emitted by the GaN-based LED is maximized.

Using the non-destructive pattern transfer method of dry etching first and then wet etching, with the help of dry etching's excellent pattern vertical transfer and rate control characteristics, the submicron-scale natural photolithographic pattern is transferred to the etching mask layer 6, and the pattern is removed Most of the nanobody layer 5 in the region, and finally the remaining nanobody layer 5 is completely removed by means of selective wet etching between SiO ₂ and Si ₃ N ₄ to obtain nanopillars 2, which fundamentally avoids damage to the p-GaN substrate 1 Cause surface damage, will not affect the electrical characteristics of the LED.

Claims (10)

1. A high light extraction efficiency GaN-based LED transparent electrode structure, comprising a GaN substrate (1); It is characterized in that: a nano-column layer is set on the GaN substrate (1) and an ITO layer covering the nano-column layer ( 4); the nanocolumn layer includes several nanocolumns (2), and the ITO layer (4) is covered on the nanocolumn (2), and is filled in the column isolation holes (3) on both sides of the nanocolumn (2), to The ITO layer (4) is brought into ohmic contact with the GaN substrate (1). 2. The high light extraction efficiency GaN-based LED transparent electrode structure according to claim 1, characterized in that: the nanocolumn (2) is a silicon nitride nanocolumn, and the height and diameter of the nanocolumn (2) are all located at 1/2. 4λ˜λ, where λ is the wavelength of light emitted by the GaN-based LED. 3. A method for preparing a GaN-based LED transparent electrode structure with high light extraction efficiency, characterized in that, the method for preparing the transparent electrode structure comprises the steps: (a), providing a GaN substrate (1), and setting a nanobody layer (5) on the GaN substrate (1); (b), setting an etching mask layer (6) on the nanobody layer (5), and the etching mask layer (6) covers the nanobody layer (5); (c), setting nano-thin layer (7) on above-mentioned etching mask layer (6); (d), the above-mentioned nano-thin layer (7) is annealed to agglomerate into several nano-dots (8) densely arranged on the etching mask layer (6), and form nano-dots outside the nano-dots (8) hole(9); (e), using the nano-dot (8) as a mask, dry etching the etching mask layer (6) and the nano-body layer (5), to remove the etching corresponding to the position of the nano-dot hole (9) Etching the mask layer (6) and part of the nanobody layer (5) below the etching mask layer (6), to obtain an etching mask block (12) positioned below the nano dot (8); (f), remove above-mentioned nano dots (8), and utilize described etching mask block (12) to carry out wet etching to nanobody layer (5), to remove the nano soma(5); (g), removing the above-mentioned etching mask block (12) to obtain several disconnected nanocolumns (2); (h) Depositing an ITO layer (4) on the above-mentioned nanocolumn (2), and annealing the ITO layer (4), so that the ITO layer (4) is in ohmic contact with the GaN substrate (1). 4. according to the preparation method of the GaN-based LED transparent electrode structure with high light extraction efficiency described in claim 3, it is characterized in that: the GaN substrate (1) is a P-GaN substrate, and the nanobody layer (5) is deposited on GaN by PECVD A silicon nitride layer on a substrate (1). 5. According to the preparation method of the GaN-based LED transparent electrode structure with high light extraction efficiency according to claim 3, it is characterized in that: the etching mask layer (6) is a carbon dioxide deposited on the nano-column layer (5) by PECVD. silicon layer. 6. The method for preparing a GaN-based LED transparent electrode structure with high light extraction efficiency according to claim 3, characterized in that: the nano-thin layer (7) is an Ag layer evaporated by electron beam or magnetron sputtering. 7. The method for preparing a GaN-based LED transparent electrode structure with high light extraction efficiency according to claim 6, characterized in that: the temperature range for the annealing of the nano-thin layer (7) to form the nano-dots (8) is 450°C-550°C. 8. The method for preparing a GaN-based LED transparent electrode structure with high light extraction efficiency according to claim 3, characterized in that: the diameter of the nano-dots (8) is 200nm-500nm. 9. The method for preparing a GaN-based LED transparent electrode structure with high light extraction efficiency according to claim 3, characterized in that: the ITO layer (4) is annealed so that the ITO layer (4) is in ohmic contact with the GaN substrate (1) The temperature is 450°C-650°C. 10. The method for preparing a GaN-based LED transparent electrode structure with high light extraction efficiency according to claim 3, characterized in that: the nanocolumn (2) is a silicon nitride nanocolumn, and the height and diameter of the nanocolumn (2) are located at 1/4λ˜λ, where λ is the wavelength of light emitted by the GaN-based LED.