CN113206174B - Deep ultraviolet LED hetero-epitaxial substrate and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the field of semiconductor devices, and particularly relates to a deep ultraviolet LED hetero-epitaxial substrate, a preparation method and application thereof, wherein the hetero-epitaxial substrate is a composite substrate consisting of a nano sheet and a sapphire substrate; the nano-sheets uniformly and physically cover the surface of the sapphire substrate, the melting point of the nano-sheets is higher than the growth temperature of the deep ultraviolet LED epitaxial material, and the diameter of the surface of the nano-sheets is 5-1000 nm. The composite substrate can be prepared by spin coating or spraying the nanosheets on the surface of the sapphire substrate in the form of a solution and drying, and can be applied to a deep ultraviolet LED. The substrate is formed by compounding the nano sheets and the sapphire substrate, and the epitaxial material cannot nucleate on the nano sheets, so that the healing process of the epitaxial material can be delayed, most of dislocation is bent due to the image force in the healing process, only a small amount of dislocation continues to extend upwards, the dislocation density at the surface of the epitaxial layer is effectively reduced, and the crystal quality of the deep ultraviolet LED is improved.

Description

A kind of heteroepitaxial substrate of deep ultraviolet LED and its preparation method and application

technical field

The invention belongs to the field of semiconductor devices, and more particularly, relates to a deep-ultraviolet LED heteroepitaxial substrate and a preparation method and application thereof.

Background technique

Although ultraviolet rays cannot be sensed by human eyes, they are widely used, especially deep ultraviolet rays with wavelengths less than 280 nm, which play an important role in sterilization, air purification, water purification, biological detection, and non-line-of-sight communication. As a traditional deep ultraviolet light source, the mercury lamp contains highly toxic mercury metal, which is extremely harmful to the human body and the environment. At the same time, the disadvantages of large size, high power consumption and high voltage of mercury lamps are very unfavorable for their application in daily life and special environments. In 2020, China will ban the production and use of high-pressure mercury lamps, mercury-containing fluorescent lamps and other products in accordance with the requirements of the United Nations' Minamata Convention on Mercury. Therefore, the development of a new type of high-efficiency deep ultraviolet light source to replace the traditional mercury lamp is not only the development trend of deep ultraviolet light source, but also an urgent need for the sustainable development of my country's economy and society.

AlGaN is a direct bandgap wide bandgap semiconductor material, its band gap can be continuously adjusted by changing the doping amount of Al element from 3.4eV (GaN) to 6.2eV (AlN) to achieve a spectral range from 365nm to 200nm. It emits light, and has excellent properties such as stable physical and chemical properties, high temperature resistance, and radiation resistance. It is the best candidate material for the preparation of semiconductor deep ultraviolet light source devices. Moreover, compared with traditional mercury lamps, AlGaN-based deep ultraviolet light-emitting diodes (LEDs) have many advantages such as small size, low power consumption, environmental protection, safety and integration, and are expected to achieve breakthrough progress and huge applications in the next few years. received more and more attention and attention.

At present, deep ultraviolet LEDs mainly use sapphire as a heteroepitaxial substrate. However, there are large differences in lattice constant and thermal expansion coefficient between sapphire and epitaxial materials. In the process of heteroepitaxial growth, due to lattice mismatch, defects such as high-density grain boundaries and dislocations (up to 10 ⁹ cm ^{- 2} magnitude). Some of these defects will penetrate into the active region of the quantum well, resulting in a non-radiative recombination center, which directly affects the quantum efficiency of the device.

SUMMARY OF THE INVENTION

The present invention provides a deep-ultraviolet LED heteroepitaxial substrate, a preparation method and application thereof, and is used to solve the technology of existing high-density grain boundaries and dislocation defects in the heteroepitaxially grown thin film material on the existing sapphire substrate. question.

The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a heteroepitaxial substrate for deep ultraviolet LED, which is a composite substrate composed of nano-sheets and a sapphire substrate; wherein, the nano-sheets are evenly physically covered on the sapphire substrate. The surface of the substrate, the melting point of the nanosheet is higher than the growth temperature of the deep ultraviolet LED epitaxial material, and the diameter of the surface is 5-1000 nm.

The beneficial effects of the present invention are as follows: the present invention adopts nanosheets and sapphire substrates to form a composite substrate, and the epitaxial material cannot nucleate on the nanosheets, so the healing process of the epitaxial material can be delayed. The dislocations caused by the mismatch between the lattice of the material and the sapphire are bent due to the mirror force, and only a small amount of dislocations continue to extend upward, which can effectively reduce the dislocation density at the surface of the epitaxial layer and improve the crystal quality of the deep ultraviolet LED.

On the basis of the above technical solutions, the present invention can also be improved as follows.

Further, the nanosheets are graphene nanosheets.

Further, the nanosheets are boron nitride nanosheets.

The further beneficial effects of the present invention are that both the graphene nanosheet material and the boron nitride nanosheet material have high thermal conductivity, and the composite substrate prepared by using this nanosheet can make the heat of the device use process pass through the graphene nanosheets. Flakes or boron nitride nanosheets are exported, which improves the heat dissipation performance of the device, thereby realizing high-efficiency deep ultraviolet LED chips.

The present invention also provides a method for preparing the above-mentioned deep ultraviolet LED heteroepitaxial substrate. The nanosheets are spin-coated or sprayed on the surface of the sapphire substrate in the form of a solution, and are prepared by drying.

The beneficial effects of the invention are: the composite substrate can be prepared by spin coating or spraying, the process is simple, and the industrial application is convenient.

The present invention also provides a deep ultraviolet LED device using the above-mentioned heteroepitaxial substrate.

The beneficial effects of the present invention are: based on the above proposed composite substrate to grow the deep ultraviolet LED structure, lateral epitaxial growth can be realized, and the dislocation density of the epitaxial material can be effectively reduced.

Further, the structure from bottom to top is the heteroepitaxial substrate, AlN intrinsic layer, N-type AlGaN electron injection layer, quantum well active region, P-type AlGaN electron blocking layer and p-type GaN layer.

The present invention also provides a method for preparing the deep ultraviolet LED device as described above, comprising:

The heteroepitaxial substrate of the deep ultraviolet LED as described above is directly placed in a metal organic compound chemical vapor deposition system to sequentially grow AlN intrinsic layer, N-type AlGaN electron injection layer, quantum well active region, and P-type AlGaN electron blocking layer. layer and P-type GaN layer.

First, the nanosheets are spin-coated or sprayed on the surface of the sapphire substrate in the form of a solution, and the heteroepitaxial substrate of the deep ultraviolet LED as described above is prepared by drying, and then the heteroepitaxial substrate is placed on the metal organic compound In the chemical vapor deposition system, an AlN intrinsic layer, an N-type AlGaN electron injection layer, a quantum well active region, a P-type AlGaN electron blocking layer and a P-type GaN layer are sequentially grown.

Description of drawings

1 is a schematic diagram of the mechanism of reducing the dislocation density of AlN epitaxial materials provided by the nanosheet/sapphire composite substrate according to an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a deep ultraviolet LED grown on a nanosheet/sapphire composite substrate according to an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Example 1

A heteroepitaxial substrate for deep ultraviolet LED, which is a composite substrate composed of nanosheets and sapphire substrate; wherein, the nanosheets evenly physically cover the surface of the sapphire substrate, and the melting point of the nanosheets is higher than that of the deep ultraviolet The growth temperature of the LED epitaxial material, and the surface diameter is 5-1000nm.

Compared with the common sapphire substrate, the nanosheet/sapphire composite substrate proposed in this embodiment can reduce the dislocation density in the LED and improve the efficiency of the device. The main mechanism is: as shown in Figure 1, since the epitaxial material cannot nucleate on the nanosheets, the healing process of the epitaxial material can be delayed, and more dislocations are bent and annihilated during the healing process, thereby improving the crystallinity of the deep ultraviolet LED. quality. Specifically, when growing an AlN epitaxial material on a sapphire substrate, generally speaking, due to the mismatch between the lattices of the AlN epitaxial material and the sapphire substrate, the AlN epitaxial material has high dislocations, as shown in the left figure of Figure 1, Its density can reach 10 ⁹ cm ^-2 . These dislocations form non-radiative recombination centers, reducing the luminous efficiency of LEDs. In response to this problem, this embodiment proposes a nanosheet/sapphire composite substrate. As shown in the right image of Fig. 1, since AlN epitaxial material cannot grow in the area covered by nanosheets, the healing process of AlN epitaxial material can be delayed, and during the healing process, most dislocations are bent due to the mirror force, and only A small number of dislocations continue to extend upward, effectively reducing the dislocation density at the surface of the epitaxial layer, and improving the crystal quality of the deep ultraviolet LED.

It should be noted that, first of all, the melting point of the selected nanosheets is higher than the growth temperature of the deep ultraviolet LED epitaxial material, and will not be completely decomposed during the growth of the epitaxial material, and the atoms generated by the decomposition of the nanosheet material at high temperature do not have the lattice structure of the epitaxial material. make an impact. Secondly, the surface diameter of the selected nanosheets is 5-1000nm. This size is taken into account: the epitaxial layer will eventually grow flat on the surface of the substrate. If the nanosheets are too large, there will be too many areas where AlN epitaxial materials cannot be grown. The epitaxial material cannot grow flat during the subsequent healing process. Therefore, under the condition of the size of the conventional sapphire substrate, the selection of nano-sized nanosheets can ensure the long and flat epitaxial layer and achieve the purpose of reducing the dislocation density. In addition, since there are no dangling bonds on the surface of the nanosheets, the aforementioned epitaxial materials cannot nucleate on the nanosheets.

Preferably, the nanosheets are graphene nanosheets or boron nitride nanosheets.

The traditional sapphire substrate not only easily leads to defects such as dislocation density in the growth of epitaxial materials as mentioned above, but also has poor thermal conductivity, which is not conducive to the heat dissipation of ultraviolet LED devices. In this embodiment, graphene nanosheet materials and boron nitride nanosheet materials are preferred, which have high thermal conductivity. By using this composite substrate, the heat during the use of the device can pass through graphene nanosheets or boron nitride nanosheets. Export, improve the heat dissipation performance of the device, thereby realizing a high-efficiency deep ultraviolet LED chip. Therefore, compared with ordinary sapphire substrates, graphene nanosheets/sapphire composite substrates or boron nitride nanosheets/sapphire composite substrates can improve the thermal stability of LEDs.

Embodiment 2

A method for preparing a deep ultraviolet LED heteroepitaxial substrate according to the first embodiment, spin-coating or spraying nanosheets on the surface of a sapphire substrate in the form of a solution, and preparing by drying.

The composite substrate can be prepared by spin coating or spray coating, the process is simple, and the industrial application is convenient.

Embodiment 3

A deep ultraviolet LED device adopts the heteroepitaxial substrate as described in the first embodiment.

Based on the composite substrate growth of the deep ultraviolet LED structure proposed in the first embodiment, lateral epitaxial growth can be realized, and the dislocation density of the epitaxial material can be effectively reduced.

Preferably, the structure from bottom to top is the above heteroepitaxial substrate, AlN intrinsic layer, N-type AlGaN electron injection layer, quantum well active region, P-type AlGaN electron blocking layer and P-type GaN layer.

As shown in Figure 2, a novel graphene nanosheet/sapphire composite substrate can effectively improve the optical power and heat dissipation performance of deep ultraviolet LEDs. Its structure includes: a graphene nanosheet/sapphire composite substrate; an AlN intrinsic layer; an N-type AlGaN electron injection layer; a quantum well active region; a P-type AlGaN electron blocking layer; and a P-type GaN layer.

Embodiment 4

A preparation method of deep ultraviolet LED as described in Embodiment 3, comprising:

The heteroepitaxial substrate of the deep ultraviolet LED as described in the first embodiment is directly placed in the metal organic compound chemical vapor deposition system to grow AlN intrinsic layer, N-type AlGaN electron injection layer, quantum well active region, P-type sequentially. AlGaN electron blocking layer and P-type GaN layer.

First, spin-coating or spraying nanosheets on the surface of the sapphire substrate in the form of a solution, and prepare the heteroepitaxial substrate of the deep ultraviolet LED as described in Example 1 by drying, and then place the heteroepitaxial substrate on the surface of the sapphire substrate. The AlN intrinsic layer, the N-type AlGaN electron injection layer, the quantum well active region, the P-type AlGaN electron blocking layer and the P-type GaN layer are sequentially grown in the metal organic compound chemical vapor deposition system.

Specifically, taking graphene nanosheets as an example, the preparation conditions of each layer are as follows:

1) Graphene nanosheet/sapphire composite substrate: Graphene nanosheets with a diameter of 5nm-1000nm are deposited (evenly covered) on the surface of the sapphire substrate by spin coating (500-5000 rpm) or spraying , and then the substrate was baked in an oven for 24h (temperature 50-200°C).

2) AlN intrinsic layer: put the substrate in step 1 into the metal organic compound chemical vapor deposition system to start growing the AlN layer. The growth temperature is 1200°C to 1400°C, the thickness is 500 nm to 4000 nm, the Al source in the growth process is trimethyl aluminum, the Ga source is trimethyl gallium or triethyl gallium, and the N source is ammonia gas.

3) N-type AlGaN electron injection layer: the growth temperature is 800°C to 1200°C, the Al composition is 20% to 90%, and the thickness is 500nm to 4000nm. Si is used as the n-type dopant.

4) Quantum well active region: the growth temperature is 700℃～1100℃, the potential barrier thickness is 5nm～30nm, the Al composition is 20%～100%, the potential well thickness is 0.1nm～5nm, and the Al composition is 0 %～80%.

5) P-type AlGaN electron blocking layer: the growth temperature is 700°C to 1100°C, the thickness is 10 nm to 50 nm, and the Al composition thereof is 50% to 90%.

6) P-type GaN layer: the growth temperature is 400°C to 900°C, the thickness is 1-200 nm, and Mg is used as a p-type dopant.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (5)

1. A hetero-epitaxial substrate of a deep ultraviolet LED is characterized in that the hetero-epitaxial substrate is a composite substrate composed of a nano-sheet and a sapphire substrate; the nano sheets uniformly and physically cover the surface of the sapphire substrate, the melting point of the nano sheets is higher than the growth temperature of the deep ultraviolet LED epitaxial material, and the diameter of the surface of the nano sheets is 5-1000 nm; wherein the nano sheet is a graphene nano sheet or a boron nitride nano sheet.

2. The preparation method of the heteroepitaxial substrate of the deep ultraviolet LED as claimed in claim 1, characterized in that the nanosheets are spin-coated or spray-coated on the surface of the sapphire substrate in the form of a solution and are prepared by drying.

3. A deep ultraviolet LED device, characterized in that a heteroepitaxial substrate according to claim 1 is used.

4. The deep ultraviolet LED device of claim 3, wherein the structure of the deep ultraviolet LED device is, from bottom to top, the hetero-epitaxial substrate, the AlN intrinsic layer, the N-type AlGaN electron injection layer, the quantum well active region, the P-type AlGaN electron blocking layer and the P-type GaN layer.

5. A method for preparing the deep ultraviolet LED device according to claim 4, which comprises the following steps:

directly placing the heteroepitaxial substrate of the deep ultraviolet LED of claim 1 in a metal organic compound chemical vapor deposition system to sequentially grow an AlN intrinsic layer, an N-type AlGaN electron injection layer, a quantum well active region, a P-type AlGaN electron blocking layer and a P-type GaN layer;

firstly, spin-coating or spraying nano-sheets on the surface of a sapphire substrate in a solution mode, drying to obtain the hetero-epitaxial substrate of the deep ultraviolet LED according to claim 1, and then placing the hetero-epitaxial substrate in a metal organic compound chemical vapor deposition system to sequentially grow an AlN intrinsic layer, an N-type AlGaN electron injection layer, a quantum well active region, a P-type AlGaN electron blocking layer and a P-type GaN layer.

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