WO2018040123A1

WO2018040123A1 - Led epitaxial wafer grown on scandium magnesium aluminum oxide substrate and preparation method therefor

Info

Publication number: WO2018040123A1
Application number: PCT/CN2016/098633
Authority: WO
Inventors: 李国强; 王文樑; 杨为家
Original assignee: 华南理工大学
Priority date: 2016-08-29
Filing date: 2016-09-10
Publication date: 2018-03-08
Also published as: CN106257694A

Abstract

An LED epitaxial wafer grown on a scandium magnesium aluminum oxide substrate, comprising: a GaN buffer layer (11) grown on the scandium magnesium aluminum oxide substrate (10), an Al nano-island layer (12) grown on the GaN buffer layer (11), an undoped GaN layer (13) grown on the Al nano-island layer (12), an n-type doped GaN film (14) grown on the undoped GaN layer (13), an InGaN/GaN quantum well (15) grown on the n-type doped GaN film (14), a p-type doped GaN film (16) grown on the InGaN/GaN quantum well (15). Also disclosed is a method for preparing the above LED epitaxial wafer grown on a scandium magnesium aluminum oxide substrate. The present invention has the advantages of having a simple growth process and low preparation cost; and, the prepared LED epitaxial wafer features flat surfaces, low defect-density and good photoelectric performances.

Description

LED epitaxial wafer grown on magnesium aluminate ruthenium substrate and preparation method thereof

Technical field

The invention relates to an LED epitaxial wafer and a preparation method thereof, in particular to an LED epitaxial wafer grown on a magnesium aluminate strontium aluminate (ScMgAlO ₄ ) substrate and a preparation method thereof.

Background technique

GaN and its related Group III nitrides have excellent electrical, optical and acoustic properties and have been widely used in the fabrication of light-emitting diodes (LEDs), laser diodes (LDs) and field effect transistors.

Commercial LEDs are primarily epitaxially grown on sapphire substrates. On the one hand, due to the lattice mismatch of sapphire and GaN as high as 13.3%, the formation of high dislocation density in the epitaxial GaN film process reduces the carrier mobility of the material, shortens the carrier lifetime, and ultimately affects The performance of GaN-based devices. On the other hand, since the thermal mismatch between sapphire heat and GaN is as high as 27% at room temperature, when the epitaxial layer is grown, the device will generate a large compressive stress from the high temperature of epitaxial growth to room temperature, which may easily lead to Cracking of the film and substrate. In addition, since the thermal conductivity of sapphire is low, 25 W/m·K at room temperature, it is difficult to discharge the heat generated in the chip in time, resulting in heat accumulation, which reduces the internal quantum efficiency of the device and ultimately affects the performance of the device.

Therefore, new substrate materials such as silicon (Si), partial metals (Al, Cu, etc.) and lanthanum aluminate (La _0.3 Sr _1.7 AlTaO ₆ ) and lithium gallate (LiGaO ₂ ) are used for epitaxial growth of GaN thin films. . However, the growth of GaN thin films on these substrates still faces many problems. For example, although the Si substrate is inexpensive and large in size, the lattice mismatch between the Si substrate and the epitaxial layer is large; the metal substrate having high thermal conductivity is mostly a face-centered cubic structure or a body-centered cubic structure, and the grown The GaN film is prone to other impurity phases; the La _0.3 Sr _1.7 AlTaO ₆ and LiGaO ₂ substrate has a lower lattice mismatch between the GaN film, but the preparation process of the large-sized substrate is difficult, and the quality of the substrate single crystal is poor. It is not conducive to the growth of high quality GaN thin films and the industrialization of high performance GaN thin film devices. Therefore, it is urgent to find a substrate material with superior comprehensive performance in terms of matching degree, quality and cost for epitaxial growth of GaN thin films.

Summary of the invention

In order to overcome the above disadvantages and disadvantages of the prior art, it is an object of the present invention to provide a growth in On the LED epitaxial wafer on the magnesium aluminate ruthenium substrate, the selected magnesium aluminate ruthenium substrate material has a small lattice mismatch with GaN (1.8%) and a small thermal mismatch (9.7%).

Another object of the present invention is to provide a method for preparing the above-mentioned LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate, which has simple growth process and low preparation cost, and the prepared LED epitaxial wafer has a flat surface, low defect density and good photoelectric performance. .

The object of the invention is achieved by the following technical solutions:

An LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate, comprising a GaN buffer layer grown on a magnesium aluminate ruthenium substrate, an Al nano island layer grown on the GaN buffer layer, and a non-growth on the Al nano island layer Doped GaN layer, n-doped GaN thin film grown on undoped GaN layer, InGaN/GaN quantum well grown on n-doped GaN thin film, p-type doped on InGaN/GaN quantum well GaN film.

The magnesium aluminate ruthenium substrate has an epitaxial plane with a (0001) plane offset (11-20) plane of 0.5 to 1°.

The GaN buffer layer has a thickness of 50 to 100 nm.

The Al nano island layer has a thickness of 50 to 200 nm.

The undoped GaN layer has a thickness of 200 to 300 nm.

The n-type doped GaN thin film has a thickness of 3 to 5 μm, and the n-type doped GaN thin film has a concentration of 5 to 9 × 10 ¹⁸ cm ^-3 .

The InGaN/GaN quantum well is an InGaN well layer/GaN barrier layer of 7 to 10 cycles, wherein the thickness of the InGaN well layer is 2 to 3 nm; and the thickness of the GaN barrier layer is 10 to 13 nm.

The p-type doped GaN thin film has a thickness of 250 to 350 nm, and the p-type doped GaN thin film has a doping concentration of 2 to 5 × 10 ¹⁸ cm ^-3 .

The method for preparing an LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate comprises the following steps:

(1) Selection of substrate and its crystal orientation: using a magnesium aluminate ruthenium substrate with an epitaxial plane of (0001) plane (11-20) plane 0.5~1°, the crystal epitaxial orientation relationship is: GaN (0001) The face is parallel to the (0001) face of the ScMgAlO ₄ substrate;

(2) Substrate annealing treatment, the specific process of the annealing is: placing the substrate into a molecular beam epitaxial vacuum growth chamber, and annealing the ScMgAlO ₄ substrate at 600 to 700 ° C for 1 to 2 h to obtain atomic level flattening. Substrate surface

(3) Epitaxial growth of GaN buffer layer: the substrate temperature is adjusted to 450-550 ° C, and the pressure in the reaction chamber is 1.0-4.0×10-5 Pa and the laser energy density is 1.5-3.0 J/cm ² by pulse laser deposition. a GaN buffer layer is grown under conditions; a buffer layer is grown at 450 to 550 ° C;

(4) Epitaxial growth of Al nano-island layer: by molecular beam epitaxial growth process, the substrate is maintained at 700-900 ° C, the flow rate of N ₂ is 0.1-2 sccm, and the evaporation temperature of Al source is 1100-1200 ° C, in step (3) Growing an Al nano island layer on the obtained GaN buffer layer;

(5) Epitaxial growth of an undoped GaN layer: a molecular beam epitaxial growth process is employed to maintain the substrate at 500 to 600 ° C, a pressure in the reaction chamber of 6.0 to 8.0 × 10 ^-5 Pa, and a growth rate of 0.6 to 0.8. An undried GaN layer is grown on the Al nano island layer obtained in the step (4) under ML/s conditions;

(6) Epitaxial growth of n-type doped GaN thin film: by molecular beam epitaxial growth process, the substrate temperature is raised to 650-750 ° C, the reaction chamber pressure is 6.0-8.0×10 ^-5 Pa, and the growth rate is 0.6- An n-type doped GaN film is grown on the undoped GaN layer obtained in step (5) under conditions of 0.8 ML/s;

(7) Epitaxial growth of InGaN/GaN multiple quantum wells: using molecular beam epitaxial growth process, the growth temperature is 650-750 ° C, the pressure in the reaction chamber is 1.0-2.0×10 ^-5 Pa, and the growth rate is 0.2-0.4 ML. In the condition of /s, growing an InGaN/GaN multiple quantum well on the n-type doped GaN film obtained in the step (6);

(8) Epitaxial growth of p-type doped GaN thin film: The molecular temperature is adjusted to 650-750 ° C by a molecular beam epitaxial growth process, the pressure of the reaction chamber is 6.0-8.0×10 ^-5 Pa, and the growth rate is 0.6-0.8 ML. Under the condition of /s, a p-type doped GaN thin film is grown on the InGaN/GaN multiple quantum well obtained in the step (7).

Compared with the prior art, the present invention has the following advantages and benefits:

(1) The present invention uses magnesium aluminate ruthenium as a substrate, and the magnesium aluminate ruthenium crystal belongs to a hexagonal crystal system, which has a small lattice mismatch with GaN (1.8%) and a small thermal mismatch (9.7%), and is easy to grow hexagonal phase. GaN does not appear in other impurity phases; the thermal conductivity of magnesium aluminate is much higher than that of sapphire, which is beneficial to the heat dissipation of the device and improves the performance of the device; the preparation process of the large-sized magnesium aluminate ruthenium substrate is relatively simple and easy to obtain. The price is cheap, which is favorable for reducing the production cost; the magnesium aluminate ruthenium substrate used in the invention has high crystal quality, and the (0001) plane has a half-width (FWHM) value of XRD rocking curve of only 20 arcsec.

(2) The present invention uses magnesium aluminate bismuth as a substrate, and uses a low temperature (450-550 ° C) epitaxial technique to epitaxially grow a GaN buffer layer on a magnesium aluminate substrate by pulsed laser deposition to grow GaN. The buffer layer can obtain island-like GaN, paving the next step for depositing high-quality low-defect GaN film, improving the luminous efficiency of the device, and it is expected to prepare a high-efficiency LED device.

(3) The molecular beam epitaxial growth process of the present invention produces a high-quality Al nano-island layer having a thickness of 50 to 200 nm; the Al nano-island layer is advantageous for subsequent nucleation and growth of GaN, and improves the crystal quality of the LED; The nano-island layer can increase the reflection of light, thereby increasing the light-emitting efficiency of the LED.

(4) The molecular beam epitaxial growth process of the present invention produces a high quality GaN film having a thickness of 200 to 300 nm; when the GaN thickness is 200 to 300 nm, GaN is in a fully relaxed state, which is advantageous for a later high quality n-type doping. Epitaxial growth of a hetero-GaN film.

(5) The invention adopts magnesium strontium aluminate with superior comprehensive performance as the substrate, can effectively reduce the formation of dislocations, and effectively dope the GaN film, and prepare a high-quality GaN film, which is advantageous for improving carriers. The radiation recombination efficiency can greatly improve the luminous efficiency of nitride devices such as semiconductor lasers, light-emitting diodes and solar cells. Taking the LED epitaxial wafer prepared by the invention as an example, the doping concentration of the n-GaN layer is 5 to 9×10 ¹⁸ cm ^-3 , and the doping concentration of the p-GaN layer is 2 to 5×10 ¹⁸ cm ^-3 . The photoelectric performance of the test wafer level LED chip without cutting the chip is as follows: at a high operating current of 350 mA, the chip has a forward bias voltage of 2.6 V and an output power of 640 mW. The test data confirms that the LED chip fabricated by the invention has excellent photoelectric performance and has a good application prospect.

DRAWINGS

1 is a schematic cross-sectional view of an LED epitaxial wafer prepared in Example 1.

Figure 2 is a RHEED photograph of an Al nano island layer.

3 is a micrograph of an epitaxial wafer of an LED prepared in Example 1.

4 is a low temperature and room temperature photoluminescence (PL) spectrum of the LED epitaxial wafer prepared in Example 1.

5 is an optical power-current map of an epitaxial wafer of an LED prepared in Example 1.

detailed description

The present invention will be further described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto.

Example 1

The method for preparing an LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate of the present embodiment comprises the following steps:

(1) Selection of substrate and its crystal orientation: using a magnesium aluminate ruthenium substrate with an epitaxial plane of (0001) plane (11-20) plane 0.5~1°, the crystal epitaxial orientation relationship is: GaN (0001) The face is parallel to the (0001) face of ScMgAlO ₄ ;

(2) substrate annealing treatment, the specific process of the annealing is: the substrate molecular beam epitaxial vacuum growth chamber, the magnesium aluminate ruthenium substrate is annealed at 600 ° C for 1 hour to obtain an atomic level flat surface;

(3) epitaxial growth of GaN buffer layer: the substrate temperature was adjusted to 450 ° C, and the thickness was grown by pulse laser deposition technique under the conditions of a pressure of 1.0×10 ^-5 Pa in the reaction chamber and a laser energy density of 2.0 J/cm ² . 50 nm GaN buffer layer;

(4) Al nano island layer epitaxial growth: the substrate temperature is adjusted to 750 ° C, the Al nano island layer having a thickness of 50 nm is grown under the condition that the N ₂ flow rate is 0.5 sccm and the Al source evaporation temperature is 1200 ° C;

(5) Epitaxial growth of an undoped GaN layer: using a molecular beam epitaxial growth process, the substrate is maintained at 500 ° C, and the pressure in the reaction chamber is 6.0 × 10 ^-5 Pa, and the growth rate is 0.6 ML / s. An undoped GaN layer having a thickness of 200 nm is grown on the Al nano island layer obtained in the step (3);

(6) Epitaxial growth of n-type doped GaN thin film: using a molecular beam epitaxial growth process, the substrate temperature was raised to 650 ° C, and the reaction chamber pressure was 6.0 × 10 ^-5 Pa and the growth rate was 0.6 ML / s. An n-type doped GaN film having a thickness of 3 μm is grown on the undoped GaN layer obtained in the step (4), and the doping concentration of the n-GaN layer is 5×10 ¹⁸ cm ⁻³ ;

(7) Epitaxial growth of InGaN/GaN multiple quantum wells: a molecular beam epitaxial growth process with a growth temperature of 650 ° C, a pressure of 1.0 × 10 ^-5 Pa in the reaction chamber, and a growth rate of 0.2 ML/s. An InGaN/GaN multiple quantum well is grown on the n-type doped GaN film obtained in the step (5); the InGaN/GaN quantum well is a 7-cycle InGaN well layer/GaN barrier layer, wherein the thickness of the InGaN well layer is 2 nm, The thickness of the GaN barrier layer is 10 nm;

(8) Epitaxial growth of p-type doped GaN thin film: using a molecular beam epitaxial growth process, the substrate temperature was adjusted to 650 ° C, the pressure in the reaction chamber was 6.0 × 10 ^-5 Pa, and the growth rate was 0.6 ML / s. Next, a p-type doped GaN thin film having a thickness of 250 nm grown on the InGaN/GaN multiple quantum well obtained in the step (6), and a p-GaN layer doping concentration of 2 × 10 ¹⁸ cm ^-3 . It was determined that the roughness RMS value of the p-type doped GaN thin film prepared in this example was less than 1.5 nm; indicating that a p-doped GaN thin film showing high quality was obtained.

As shown in FIG. 1, the LED epitaxial wafer grown on the ScMgAlO ₄ substrate prepared in this embodiment includes a GaN buffer layer 11 grown on the ScMgAlO ₄ substrate 10, and an Al nano island layer grown on the GaN buffer layer 11. 12, an undoped GaN layer 13 grown on the Al nano island layer 12, an n-type doped GaN thin film 14 grown on the undoped GaN layer 13, and InGaN/GaN grown on the n-type doped GaN thin film 14. The quantum well 15 is a p-type doped GaN thin film 16 grown on the InGaN/GaN quantum well 15.

Fig. 2 is a RHEED photograph of an Al nano-island layer. From the figure, a diffraction pattern of bright dots connected to a line can be seen; it is shown that the Al nano-island layer is a single crystal and has a good crystal quality.

Figure 3 is a micrograph of an LED. It can be seen from Figure 2 that the epitaxially grown LED has no particles and defects; it indicates that a high quality LED epitaxial wafer is epitaxially grown on a ScMgAlO ₄ (0001) substrate.

4 is a PL spectrum of an epitaxial wafer of LED prepared by the present invention. The test shows that the peak position of low-temperature photoluminescence of InGaN/GaN multiple quantum well is 443 nm, the full width at half maximum is 21.0 nm, and the peak position of photoluminescence at room temperature is 445 nm. The half-height width is 22.3 nm, and the multi-quantum well on the surface has good photoelectric performance, and is an ideal material for preparing high-efficiency LED devices.

5 is an optical power-current map of an LED epitaxial wafer prepared by the present invention, which has an optical power of 370 mW at a high current of 300 mA, which meets the current lighting requirement level, and exhibits excellent electrical properties of the LED device prepared by the present invention.

Example 2

(2) substrate annealing treatment, the specific process of the annealing is: the substrate molecular beam epitaxial vacuum growth chamber, the magnesium aluminate ruthenium substrate is annealed at 700 ° C for 2 hours to obtain an atomic level flat surface;

(3) Epitaxial growth of GaN buffer layer: The substrate temperature was adjusted to 550 ° C, and the thickness was grown by pulse laser deposition technique under the conditions of a pressure of 4.0×10 ^-5 Pa in the reaction chamber and a laser energy density of 2.5 J/cm ² . 100 nm GaN buffer layer;

(4) Al nano island layer epitaxial growth: the substrate temperature is adjusted to 750 ° C, the Al nano island layer having a thickness of 100 nm is grown under the condition that the N ₂ flow rate is 1 sccm and the Al source evaporation temperature is 1200 ° C;

(5) Epitaxial growth of an undoped GaN layer: using a molecular beam epitaxial growth process, the substrate is maintained at 600 ° C, and the pressure in the reaction chamber is 8.0 × 10 ^-5 Pa and the growth rate is 0.8 ML / s. An undoped GaN layer having a thickness of 300 nm is grown on the Al nano island layer obtained in the step (3);

(6) Epitaxial growth of n-type doped GaN thin film: using a molecular beam epitaxial growth process, the substrate temperature was raised to 750 ° C, and the reaction chamber pressure was 8.0 × 10 ^-5 Pa and the growth rate was 0.8 ML / s. An n-type doped GaN film having a thickness of 5 μm is grown on the undoped GaN layer obtained in the step (4), and the doping concentration of the n-GaN layer is 9×10 ¹⁸ cm ⁻³ ;

(7) Epitaxial growth of InGaN/GaN multiple quantum wells: a molecular beam epitaxial growth process with a growth temperature of 750 ° C, a pressure of 2.0 × 10 ^-5 Pa in the reaction chamber, and a growth rate of 0.4 ML/s. An InGaN/GaN multiple quantum well is grown on the n-type doped GaN film obtained in the step (5); the InGaN/GaN quantum well is a 10-cycle InGaN well layer/GaN barrier layer, wherein the thickness of the InGaN well layer is 3 nm, The thickness of the GaN barrier layer is 13 nm;

(8) Epitaxial growth of p-type doped GaN thin film: using a molecular beam epitaxial growth process, the substrate temperature was adjusted to 750 ° C, the pressure in the reaction chamber was 8.0 × 10 ^-5 Pa, and the growth rate was 0.8 ML / s. Next, a p-type doped GaN thin film having a thickness of 350 nm grown on the InGaN/GaN multiple quantum well obtained in the step (6), and a p-GaN layer doping concentration of 5 × 10 ¹⁸ cm ^-3 .

The LED epitaxial wafer on the ScMgAlO ₄ substrate prepared in this embodiment has very good performance both in surface topography and in photoelectric performance. The test data is similar to that in Embodiment 1, and will not be described herein.

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the embodiments, and any other changes, modifications, substitutions, and combinations may be made without departing from the spirit and scope of the present invention. And simplifications, all of which are equivalent replacement means, are included in the scope of protection of the present invention.

Claims

An LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate, comprising: a GaN buffer layer grown on a magnesium aluminate ruthenium substrate, an Al nano island layer grown on the GaN buffer layer, grown on the Al nano island An undoped GaN layer on the layer, an n-type doped GaN film grown on the undoped GaN layer, an InGaN/GaN quantum well grown on the n-doped GaN film, grown on the InGaN/GaN quantum well P-type doped GaN film.
The LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate according to claim 1, wherein the magnesium aluminate ruthenium substrate has a (0001) plane offset (11-20) plane of 0.5 to 1 °. Epitaxial surface.
The LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate according to claim 1, wherein the GaN buffer layer has a thickness of 50 to 100 nm.
The LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate according to claim 1, wherein the Al nano-island layer has a thickness of 50 to 200 nm.
The LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate according to claim 1, wherein the undoped GaN layer has a thickness of 200 to 300 nm.
The LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate according to claim 1, wherein the n-type doped GaN thin film has a thickness of 3 to 5 μm, and the n-type doped GaN thin film has a concentration of 5 to 5 9×10 18 cm -3 .
The LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate according to claim 1, wherein the InGaN/GaN quantum well is an InGaN well layer/GaN barrier layer of 7 to 10 cycles, wherein the InGaN well The thickness of the layer is 2 to 3 nm; the thickness of the GaN barrier layer is 10 to 13 nm.
The LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate according to claim 1, wherein the p-type doped GaN thin film has a thickness of 250 to 350 nm, and the p-type doped GaN thin film has a doping concentration of 2 to 5 × 10 18 cm -3 .
The method for preparing an LED epitaxial wafer grown on a magnesium aluminate ruthenium substrate according to any one of claims 1 to 8, which comprises the steps of:

(1) Selection of substrate and its crystal orientation: using a magnesium aluminate ruthenium substrate with an epitaxial plane of (0001) plane (11-20) plane 0.5~1°, the crystal epitaxial orientation relationship is: GaN (0001) The face is parallel to the (0001) face of the ScMgAlO 4 substrate;

(2) Substrate annealing treatment, the specific process of the annealing is: placing the substrate into a molecular beam epitaxy vacuum growth chamber, and annealing the ScMgAlO 4 substrate at 600-700 ° C for 1-2 h to obtain atomic level flattening. Substrate surface

(3) Epitaxial growth of GaN buffer layer: the substrate temperature is adjusted to 450-550 ° C, and the pressure in the reaction chamber is 1.0-4.0×10-5 Pa and the laser energy density is 1.5-3.0 J/cm 2 by pulse laser deposition. a GaN buffer layer is grown under conditions; a buffer layer is grown at 450 to 550 ° C;

(4) Epitaxial growth of Al nano-island layer: using molecular beam epitaxial growth process, the substrate is maintained at 700-900 ° C, the flow rate of N 2 is 0.1-2 sccm, and the evaporation temperature of Al source is 1100-1200 ° C, in step (3) Growing an Al nano island layer on the obtained GaN buffer layer;

(5) Epitaxial growth of an undoped GaN layer: a molecular beam epitaxial growth process is employed to maintain the substrate at 500 to 600 ° C, a pressure in the reaction chamber of 6.0 to 8.0 × 10 -5 Pa, and a growth rate of 0.6 to 0.8. An undried GaN layer is grown on the Al nano island layer obtained in the step (4) under ML/s conditions;

(6) Epitaxial growth of n-type doped GaN thin film: by molecular beam epitaxial growth process, the substrate temperature is raised to 650-750 ° C, the reaction chamber pressure is 6.0-8.0×10 -5 Pa, and the growth rate is 0.6- An n-type doped GaN film is grown on the undoped GaN layer obtained in step (5) under conditions of 0.8 ML/s;

(7) Epitaxial growth of InGaN/GaN multiple quantum wells: using molecular beam epitaxial growth process, the growth temperature is 650-750 ° C, the pressure in the reaction chamber is 1.0-2.0×10 -5 Pa, and the growth rate is 0.2-0.4 ML. In the condition of /s, growing an InGaN/GaN multiple quantum well on the n-type doped GaN film obtained in the step (6);

(8) Epitaxial growth of p-type doped GaN thin film: The molecular temperature is adjusted to 650-750 ° C by a molecular beam epitaxial growth process, the pressure of the reaction chamber is 6.0-8.0×10 -5 Pa, and the growth rate is 0.6-0.8 ML. Under the condition of /s, a p-type doped GaN thin film is grown on the InGaN/GaN multiple quantum well obtained in the step (7).