CN103178168A - Preparation method of air-gap photonic crystal implanted gallium nitride-based light emitting diode - Google Patents

Abstract

The invention discloses a preparation method of a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal, which comprises: laying a single-layer self-assembled close-packed ball on an n-GaN template; shrink to form a single-layer non-close-packed ball; evaporate a masking layer on the n-GaN template covered with the single-layer non-close-packed ball, wherein a certain thickness of masking layer is covered on the single-layer non-close-packed ball Layer, forming a masking layer on the ball, forming a masking layer grid at the gap between the single-layer non-close-packed balls; removing the single-layer non-close-packed balls and the masking layer on the ball, leaving the masking layer grid; The hole pattern of the masking layer grid is transferred to the n-GaN template, and the masking layer grid is removed to form an n-GaN template with a hole pattern; the n-GaN template with a hole pattern is grown to implant air gaps GaN-based light-emitting diode (LED) epitaxial wafers with PhC structure.

Description

Preparation method of GaN-based light-emitting diodes implanted with air-gap photonic crystals

technical field

The invention belongs to the technical field of semiconductors, in particular to a method for preparing gallium nitride-based light-emitting diodes implanted with air-gap photonic crystals by using self-assembly technology.

Background technique

Gallium Nitride (GaN)-based Light Emitting Diodes (LEDs) have been extensively researched and entered into large-scale commercial growth because of their excellent properties such as high light efficiency, low power consumption, and no pollution. The surface of the traditional LED epitaxial wafer is flat, because GaN itself has a high refractive index (2.52), and the total reflection effect of the air interface is serious, so that the light emitted by the active area cannot escape from the LED, and the light extraction efficiency is low. A bottleneck for efficient LEDs. People have also developed many methods to improve light extraction efficiency, including graphic substrates, p-GaN surface roughening, current spreading layer surface roughening, and integrating PhC structures in LED structures, etc., and have achieved significant results. . However, most of these methods for improving light extraction efficiency rely on expensive and complicated techniques such as electron beam lithography or nanoimprinting, which greatly limits the application of these roughening techniques in commercial LEDs. In addition, most surface roughening methods also rely on the plasma etching process, which will introduce etching defects, resulting in the absorption of photons and the degradation of electrical properties. In short, it is of great application value to seek a low-cost, large-area, and non-etching-damaged method of fabricating micro-nano patterns to improve the light extraction efficiency of LEDs.

Natural lithography is a technology that uses a naturally formed periodic or aperiodic masking layer to achieve periodic or aperiodic micro-nano-level pattern transfer, which emerged in the early 1990s. Compared with traditional etching technology, natural photolithography technology is simple and low cost. With the rapid development and progress of self-assembly technology in the chemical field in recent years, articles and patents on the use of self-assembled nanospheres for photolithography transfer (NSL) have appeared one after another. Many gratifying results have been achieved in the innovative application of transfer. The use of NSL technology can realize the transfer of submicron or even nanoscale graphics, and can also realize the production and transfer of three-dimensional graphics.

Applying natural photolithography technology to fabricate photonic crystal (PhC) structures in LEDs to improve the light extraction efficiency of LEDs has been a research hotspot in recent years. Researchers have made PhC structures on the p-GaN or current spreading layer of LEDs, which can significantly improve the light extraction efficiency of LEDs. However, the micro-nano structure on the surface of the LED is likely to damage the electrical properties of the device, and the space for improving the extraction efficiency of the LED is limited. People have begun to implant PhC structures inside LED devices, such as n-GaN, and achieved very good results.

Contents of the invention

The purpose of the present invention is to provide a method for implanting an air-gap PhC structure in the n-GaN layer of the LED by using self-assembly technology to improve the light extraction efficiency of the LED.

The invention discloses a method for preparing a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal, which comprises:

Step 1: Spread a single layer of self-assembled close-packed spheres on the n-GaN template;

Step 2: shrinking the single-layer self-assembled close-packed bead to form a single-layer non-close-packed bead;

Step 3: Evaporating a masking layer on the n-GaN template covered with the single layer of non-close-packed balls, wherein a masking layer of a certain thickness is covered on the single-layer of non-close-packed balls to form an on-ball masking layer, forming a masking layer grid at the gap between the single-layer non-close-packed balls;

Step 4: removing the single-layer non-close-packed small balls and the masking layer on the balls, leaving the masking layer grid;

Step 5: Transfer the hole pattern of the masking layer grid to the n-GaN template, and remove the masking layer grid to form an n-GaN template with the hole pattern;

Step 6: growing a GaN-based light-emitting diode (LED) epitaxial wafer implanted with an air-gap PhC structure on the n-GaN template with a hole pattern.

The above-mentioned method disclosed by the present invention uses a chemical self-assembly method to transfer patterns to an air-gap PhC structure made of n-GaN, so that part of the light conduction mode in the LED epitaxial structure becomes an escape mode, which greatly improves the extraction efficiency of the LED. Moreover, the electrical performance of the LED produced by the method is not degraded. Moreover, the method has simple process steps, low cost and is effective, and provides a good method for people to manufacture LEDs with high extraction efficiency at low cost.

Description of drawings

Fig. 1 is the flow chart of the method for preparing gallium nitride-based light-emitting diodes implanted with air-gap photonic crystals in the present invention;

Fig. 2 is a schematic diagram of the structure of a single-layer close-packed self-assembled ball on an n-GaN template when preparing a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal in the present invention;

Fig. 3 is a schematic structural diagram of etching and shrinking self-assembled spheres into single-layer non-close-packed spheres when preparing gallium nitride-based light-emitting diodes implanted with air-gap photonic crystals in the present invention;

Fig. 4 is a structural schematic diagram of covering a metal layer on an n-GaN template covered with a single layer of non-close-packed balls when preparing a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal in the present invention;

5 is a schematic structural view of an n-GaN template with a metal grid formed after removing the ball and the metal layer on the ball when preparing a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal in the present invention;

Fig. 6 is a schematic structural view of an n-GaN template with a hole pattern formed when preparing a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal according to the present invention;

Fig. 7 is a structural schematic diagram of a gallium nitride-based light-emitting diode epitaxial wafer implanted with an air-gap photonic crystal prepared in the present invention.

Fig. 8 is a scanning electron microscope (SEM) cross-sectional photo of an air-gap photonic crystal structure implanted in n-GaN in the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

Fig. 1 shows the flow chart of the method for preparing gallium nitride-based light-emitting diodes implanted with air-gap photonic crystals proposed by the present invention. As shown in Figure 1, the present invention provides a method for preparing a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal. In the process of preparing the gallium nitride-based light-emitting diode, the present invention utilizes self-assembly technology (LED) In the n-type gallium nitride (n-GaN) layer, an air-gap photonic crystal (PhC) is implanted to improve the light extraction efficiency of the LED. 2-7 show the structural schematic diagrams of different stages of the preparation of gallium nitride-based light-emitting diodes implanted with air-gap photonic crystals according to the present invention. Specifically, in a preferred embodiment of the present invention, the method includes the following steps:

Step 1: Select an n-GaN template 10 grown with a certain thickness. The thickness of the n-GaN template should be determined according to the height of the implanted air gap and the transfer depth of the hole pattern, usually between several hundred nanometers and several microns. The doping concentration is comparable to that of commercial LEDs;

Step 2: Lay a single layer of self-assembled close-packed balls 20 on the n-GaN template 10. The diameter of the balls is the period of the photonic crystal (PhC), and the size of the period depends on the impact of implanted PhC structures of different periods on the light extraction efficiency The size of the single-layer self-assembled close-packed balls can be polystyrene PS balls, silicon dioxide _SiO2 balls or one of the self-assembled balls of other materials; usually, the diameter of the ball Between 100 nanometers and 3 micrometers; FIG. 2 shows a schematic view of the structure after laying a single layer of close-packed self-assembled spheres 20;

Step 3: Etch and shrink the single-layer self-assembled close-packed spheres 20 to form a single-layer non-close-packed sphere 30; the degree of etching reduction depends on the impact of implanting PhC with different duty ratios on the light extraction efficiency and the evaporation The actual process conditions of the plating masking layer are determined; Fig. 3 shows the structure diagram of reducing the self-assembled close-packed bead into a single-layer non-close-packed bead;

Step 4: Evaporate a masking layer 40 on the n-GaN template covered with a single layer of non-close-packed balls 30, wherein the single-layer of non-close-packed balls 30 is also covered with a masking layer of a certain thickness to form an on-ball masking layer 41. A masking layer grid 42 is formed in the gaps between the non-close-packed balls 30. FIG. 4 shows a schematic structural view of an n-GaN template covered with a single layer of non-close-packed balls 30 after vapor-depositing a masking layer 40; The material of the evaporated masking layer is compatible with the etching process for hole pattern transfer in step 6, and its thickness is greater than the thickness required to withstand a certain depth of hole pattern transfer in the n-GaN template; and the evaporation masking layer method includes electron beam Evaporation (EB evaporation), magnetron sputtering (Magnetron sputtering) or one of the other methods.

Step 5: remove the non-close-packed balls 30 and the masking layer 41 on the balls, leaving the masking layer grid 42; the method of removing the balls and the masking layer on the balls can be determined according to the characteristics of the balls and the masking layer For example, if the single-layer self-assembled close-packed balls are made of polystyrene PS balls, toluene is used to ultrasonically remove the PS balls and the masking layer on the balls, or blue film or other adhesive tapes with certain adhesion can be directly used Peel off the PS pellets and the masking layer 41 on the balls; if the single-layer self- _assembled close-packed pellets 20 are SiO _pellets , you can use hydrofluoric acid solution to ultrasonically remove the single-layer non-close-packed SiO pellets and the balls. The masking layer 41 can also be peeled off with an adhesive tape. FIG. 5 shows a schematic view of the structure after removing the non-close-packed small balls 30 and the masking layer 41 on the balls;

Step 6: transfer the hole pattern of the masking layer grid 42 to the n-GaN template 10, the hole pattern has a certain depth, and then remove the masking layer grid 42 to form an n-GaN template 60 with a hole pattern 61, FIG. 6 Shows a schematic structural view of an n-GaN template 60 formed with a hole pattern 61; wherein, the transfer method can be ICP etching or other pattern transfer methods; the depth of the hole pattern transferred to the n-GaN template 10 can be 500 Nanometer to 3 microns, the specific depth is determined according to the thickness of the template, the height of the air gap left in the n-GaN template after the re-growth in step 7, and the size of the implanted air-gap photonic crystal PhC to improve the light extraction efficiency. The masking layer grid 42 should be removed to prevent contamination of the MOCVD chamber;

Step 7: Put the n-GaN template 60 with a hole pattern into the MOCVD reaction chamber to grow into an epitaxial wafer 70 of a gallium nitride-based light-emitting diode with an air-gap PhC71 structure. FIG. 7 shows the growth into an implanted Schematic diagram of the epitaxial wafer of GaN-based light-emitting diode with air-gap PhC structure. The growth of the epitaxial wafer 70 includes growing n-GaN 72, multi-quantum wells (MQWs) 73, p-type gallium nitride (p-GaN) 74 and other epitaxial layers in order on the n-GaN with hole pattern. layer. The thickness of the regrown n-GaN72 should be determined according to the influence of the distance from the implanted air gap PhC structure to the active area on the light extraction efficiency and the influence of the regrown n-GaN thickness on the electrical performance of the LED device; quantum wells, etc. The subsequent epitaxial structure can be any epitaxial structure used in commercial LEDs.

Another preferred embodiment of the method for preparing a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal proposed by the present invention is given below, the method comprising:

Step 1: Select a n-GaN template with a thickness of 2 microns;

Step 2: Spread a single layer of self-assembled close-packed PS spheres on the n-GaN template;

Step 3: shrinking the single-layer self-assembled close-packed PS spheres by RIE etching to form a single-layer non-close-packed PS spheres;

Step 4: Evaporate a metal layer Ni with a thickness of 200 nanometers on the single-layer non-close-packed PS spheres, wherein the single-layer non-close-packed PS spheres are also covered with a metal layer of a certain thickness to form a Ni metal layer on the spheres. The gap between non-close-packed PS balls is Ni metal grid;

Step 5: Remove the non-close-packed PS balls and the Ni metal layer on the balls, leaving the Ni metal grid;

Step 6: Transfer the hole pattern of the Ni metal grid to the n-GaN template, the hole pattern is 1 micron deep, and then remove the Ni metal grid to form an n-GaN template with the hole pattern;

Step 7: Put the n-GaN template with the hole pattern into the MOCVD reaction chamber, and grow a 1 micron thick regrown n-GaN layer, 5 pairs of MQWs, a 20 nm thick p-AlGaN layer and a 130 nm thick p -GaN layer forming LED epiwafer with air-gap PhC structure implanted in n-GaN.

FIG. 8 shows a scanning electron microscope (SEM) cross-sectional photo of an air-gap photonic crystal structure implanted in n-GaN by the above-mentioned method in another preferred embodiment.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (11)

1. A method for preparing a gallium nitride-based light-emitting diode implanted with an air-gap photonic crystal, comprising: Step 1: Spread a single layer of self-assembled close-packed spheres on the n-GaN template; Step 2: shrinking the single-layer self-assembled close-packed bead to form a single-layer non-close-packed bead; Step 3: Evaporating a masking layer on the n-GaN template covered with the single layer of non-close-packed balls, wherein a masking layer of a certain thickness is covered on the single-layer of non-close-packed balls to form an on-ball masking layer, forming a masking layer grid at the gap between the single-layer non-close-packed balls; Step 4: removing the single-layer non-close-packed small balls and the masking layer on the balls, leaving the masking layer grid; Step 5: Transfer the hole pattern of the masking layer grid to the n-GaN template, and remove the masking layer grid to form an n-GaN template with the hole pattern; Step 6: growing a GaN-based light-emitting diode (LED) epitaxial wafer implanted with an air-gap PhC structure on the n-GaN template with a hole pattern. 2. The preparation method according to claim 1, characterized in that the thickness of the n-GaN template in step 1 is several hundred nanometers to several micrometers. 3. the preparation method as claimed in claim 1, is characterized in that, described in step 1, single-layer self-assembled close-packed bead is polystyrene PS bead, silicon dioxide _SiO2 bead or the self-contained bead of other material Assemble one of the spheres; the diameter of the spheres is between 100 nm and 3 microns. 4. The preparation method according to claim 1, wherein in step 2, the single-layer self-assembled close-packed beads are reduced by reactive ion etching (RIE) or inductively coupled plasma (ICP) etching; Wherein, the etching gas is determined according to the material of the single-layer self-assembled close-packed balls, and the range of the distance between the balls after etching is reduced is determined according to the method and parameters of the masking layer evaporated in step 3. 5. The preparation method according to claim 1, wherein the material of the vapor-deposited masking layer in step 3 is compatible with the etching process for hole pattern transfer in step 6, and its thickness is greater than that of the n-GaN template that can bear The thickness required for the transfer of hole patterns at a certain depth; and the evaporation masking layer methods include electron beam evaporation (EB evaporation) or magnetron sputtering (Magnetron sputtering) methods. 6 . The preparation method according to claim 1 , wherein the manner of removing the single-layer non-close-packed pellets and the masking layer on the pellets in step 4 is determined according to different types of pellets. 7 . 7. The preparation method according to claim 6, wherein the single-layer self-assembled close-packed pellets are polystyrene PS pellets, and in step 4, toluene is used to ultrasonically remove the PS pellets and the masking layer on the balls, Or directly use blue film or other adhesive tape to peel off the PS ball and the masking layer on the ball. 8. preparation method as claimed in claim 6 is characterized in that, described monolayer self-assembled close-packed bead selects silicon dioxide _SiO2 bead, adopts the solution ultrasonic of hydrofluoric acid to remove _SiO2 bead in step 4 And the masking layer on the ball, or directly use tape to peel off the _SiO2 pellets and the masking layer on the ball. 9. The preparation method according to claim 1, wherein, in step 5, the hole pattern of the metal grid is transferred to the n-GaN template by ICP etching, and its depth is based on the thickness of the n-GaN template, The height of the air gap left in the regrown n-GaN and the size of the implanted air-gap photonic crystal are jointly determined to improve the light extraction efficiency. 10. The preparation method according to claim 1, characterized in that, in step 6, by putting the n-GaN template with hole pattern into the MOCVD reaction chamber, regrowing n-GaN, multiple quantum wells, p-GaN epitaxy layer, grown into an epitaxial wafer of gallium nitride-based light-emitting diodes implanted with an air-gap photonic crystal structure. 11. The preparation method according to claim 1, wherein the thickness of the regrown n-GaN in step 6 depends on the influence of the distance of the implanted air-gap PhC structure from the active region on the light extraction efficiency and The effect of the regrown n-GaN thickness on the electrical performance of the light-emitting diode device is jointly determined.

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