CN206225325U - It is grown in the GaN film on magnesium aluminate scandium substrate - Google Patents

Abstract

The utility model discloses a GaN thin film grown on a magnesium scandium aluminate substrate, comprising a GaN buffer layer, a GaN nucleation layer, a GaN amorphous layer and a GaN thin film grown sequentially on a _ScMgAlO4 substrate. In the ScMgAlO ₄ substrate, the (0001) plane deviates from the (11-20) plane by 0.5-1° as the epitaxial plane. Compared with the prior art, the utility model has the advantages of low preparation cost, and the GaN thin film has the characteristics of good crystal quality, low defect density and the like.

Description

GaN Thin Films Grown on Magnesium-Scandium Aluminate Substrates

technical field

The utility model relates to a GaN thin film, in particular to a GaN thin film grown on a magnesium-scandium aluminate (ScMgAlO ₄ ) substrate.

Background technique

GaN and III-nitrides are widely used in light-emitting diodes (LEDs), lasers, and optoelectronic devices due to their wide bandgap, stable physical and chemical properties, high thermal conductivity, and high electron saturation velocity.

Currently, GaN-based devices are mainly based on sapphire substrates. The lattice mismatch between sapphire and GaN is as high as 13.3%, which leads to the formation of high dislocation density during the epitaxial GaN film process, which reduces the carrier mobility of the material and shortens the carrier lifetime, which in turn affects GaN-based devices. performance. Secondly, since the thermal expansion coefficient of sapphire (6.63×10 ^-6 K ^-1 ) is larger than that of GaN (5.6×10 ^-6 K ^-1 ) at room temperature, the thermal mismatch between the two is about 27%. After the layer growth is completed, the process of cooling the device from the high temperature of epitaxial growth to room temperature will generate a large compressive stress, which will easily lead to cracks in the film and substrate. Third, due to the low thermal conductivity of sapphire (25W/mK at 100°C), 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, it is urgent to find a substrate material with matching lattice and thermal expansion coefficient for epitaxial growth of GaN thin films.

Utility model content

In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the purpose of this utility model is to provide a GaN film grown on a magnesium scandium aluminate substrate, and the lattice mismatch ratio between the magnesium scandium aluminate substrate material and GaN is only 1.8%, the thermal mismatch is small (9.7%), which is beneficial to the nucleation of GaN; the GaN film grown based on this substrate material has the advantages of good crystal quality and low dislocation density.

The purpose of this utility model is achieved through the following technical solutions:

The GaN thin film grown on the magnesium scandium aluminate substrate includes a GaN buffer layer, a GaN nucleation layer, a GaN amorphous layer and a GaN thin film grown on the ScMgAlO ₄ substrate in sequence.

In the ScMgAlO ₄ substrate, the (0001) plane deviates from the (11-20) plane by 0.5-1° as the epitaxial plane.

The thickness of the GaN buffer layer is 30-80nm.

The thickness of the GaN nucleation layer is 50-150 nm.

The GaN amorphous layer has a thickness of 10-120 nm.

The thickness of the GaN thin film is 100-500nm.

The preparation method of the GaN film grown on the magnesium scandium aluminate substrate comprises the following steps:

(1) Selection of the substrate and its crystal orientation: ScMgAlO ₄ substrate is used, with the (0001) plane offset from the (11-20) plane by 0.5-1° as the epitaxial plane, and the crystal epitaxial orientation relationship is: (0001) plane of GaN Parallel to the (0001) plane of ScMgAlO ₄ ;

(2) Substrate annealing treatment: put the substrate into the annealing chamber, and anneal the ScMgAlO ₄ substrate at 600-700°C for 1-2 hours to obtain an atomically flat substrate surface;

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

(4) Epitaxial growth of the GaN nucleation layer: the molecular beam epitaxy growth process is used, the substrate is kept at 500-600°C, the pressure in the reaction chamber is 6.0-8.0×10 ^-5 Pa, and the growth rate is 0.6-0.8ML Under the condition of /s, grow GaN film on the GaN buffer layer that step (3) obtains;

(5) Growth of GaN amorphous layer: using molecular beam epitaxy growth process, the substrate is kept at 350-400°C, the pressure in the reaction chamber is 1.2-2.0×10 ^-4 Pa, and the growth rate is 0.5-0.6ML/ Under the condition of s, grow a GaN amorphous layer on the GaN nucleation layer obtained in step (4), release the stress introduced in the growth;

(6) Epitaxial growth of GaN film: the molecular beam epitaxy growth process is adopted, the substrate is kept at 500-600°C, the pressure in the reaction chamber is 6.0-8.0×10 ^-5 Pa, and the growth rate is 0.6-0.8ML/s Under the condition, a GaN thin film is grown on the GaN amorphous layer obtained in step (5).

The ScAlMgO ₄ crystal belongs to the hexagonal crystal system, the lattice constant a=0.3246nm, c=2.5195nm, and has a rhombohedral hexahedral layered structure, which is similar to the structure of wurtzite nitride and zinc oxide. ScAlMgO ₄ is a substrate material that closely matches the lattice constant and structure of GaN and ZnO. Its lattice mismatch rate with GaN is about 1.8%, and its lattice mismatch rate with ZnO is only ^0.09 %. ^-6 /°C, the thermal expansion coefficient mismatch between GaN and ZnO epitaxial films is much better than that of traditional sapphire and silicon substrates, and large-scale substrates can be produced to reduce costs.

Compared with the prior art, the utility model has the following advantages and beneficial effects:

(1) The utility model uses magnesium scandium aluminate as the substrate, and the _ScMgAlO substrate has a small lattice mismatch (1.8%) with GaN, a small thermal mismatch (9.7%), and is cheap, which helps reduce production costs, The production process of magnesium scandium aluminate substrate is mature, and large-scale substrates can be produced; the thermal conductivity of ScMgAlO ₄ is higher than that of sapphire, which is conducive to the preparation of high-power devices.

(2) The utility model uses magnesium-scandium aluminate as a substrate, and before the epitaxial growth of the GaN thin film, a pulsed laser is used to deposit a low-temperature growth GaN buffer layer. The GaN buffer layer can provide a nucleation center, and it is easy to obtain island-shaped GaN, paving the way for the next step of epitaxial high-quality and low-defect GaN film.

(3) The utility model adopts the GaN amorphous layer structure. During the transformation of the GaN amorphous layer from crystal to amorphous, the stress during film growth is effectively released, and defects are reduced; thus, it is easy to grow high-quality GaN films on this basis.

(4) The GaN thin film of the present invention has a small half-width of the X-ray rocking curve, high crystal quality, and low dislocation density. In addition, magnesium-scandium aluminate with a small lattice mismatch and thermal mismatch with GaN is used as the substrate, which can effectively reduce thermal stress and dislocation formation, and is conducive to the growth of high-quality GaN thin films. The prepared GaN-based photoelectric material device has high carrier radiation recombination efficiency, and can greatly improve the luminous efficiency of nitride devices such as semiconductor lasers, light-emitting diodes and solar cells.

Description of drawings

FIG. 1 is a schematic cross-sectional view of the GaN thin film prepared in Example 1.

FIG. 2 is a high resolution X-ray diffraction (HRXRD) spectrum of the GaN thin film (GaN(0002)) prepared in Example 1.

FIG. 3 is a high-resolution X-ray diffraction (HRXRD) spectrum of the GaN thin film (GaN(10-12)) prepared in Example 1.

detailed description

The utility model will be described in further detail below in conjunction with the examples, but the implementation of the utility model is not limited thereto.

Example 1

A method for preparing a high-quality GaN film grown on a magnesium-scandium aluminate substrate, comprising the following steps:

(1) Selection of the substrate and its crystal orientation: ScMgAlO ₄ substrate is used, with the (0001) plane offset from the (11-20) plane by 0.5° as the epitaxial plane, and the crystal epitaxial orientation relationship is: the (0001) plane of GaN is parallel to (0001) plane of ScMgAlO ₄ ;

(2) Substrate annealing treatment: the magnesium scandium aluminate substrate was annealed at 600 ° C for 1 hour in the molecular beam epitaxy vacuum growth chamber of the substrate to obtain an atomically flat surface;

(3) Epitaxial growth of GaN buffer layer: the substrate temperature is adjusted to 450°C, and pulsed laser deposition is used to grow a 30nm-thick GaN buffer layer under the conditions of a reaction chamber pressure of 2.0×10 ^-5 Pa and a laser energy density of 1.8J/cm ² GaN buffer layer;

(4) Epitaxial growth of the GaN nucleation layer: the molecular beam epitaxy growth process was adopted, the substrate was kept at 500°C, the pressure of the reaction chamber was 6.0×10 ^-5 Pa, and the growth rate was 0.6ML/s. growing a GaN film with a thickness of 100 nm on the GaN buffer layer obtained in step (3);

(5) Epitaxial growth of GaN amorphous layer: the molecular beam epitaxy growth process was adopted, the substrate was kept at 550°C, the pressure of the reaction chamber was 1.6×10 ^-4 Pa, and the growth rate was 0.8ML/s. growing a GaN amorphous layer with a thickness of 120 nm on the GaN nucleation layer obtained in step (4), releasing the stress introduced during the growth;

(6) Epitaxial growth of GaN thin films: the molecular beam epitaxy growth process is adopted, the substrate is kept at 500°C, the pressure of the reaction chamber is 6.0×10 ^-5 Pa, and the growth rate is 0.6ML/s, in the step ( 5) A GaN thin film with a thickness of 200 nm is grown on the obtained GaN amorphous layer.

As shown in Figure 1, the GaN film grown on the magnesium scandium aluminate substrate prepared in this embodiment includes a GaN buffer layer 12 grown on a _ScMgAlO substrate 11; the GaN nucleation layer grown on the GaN buffer layer 12 layer 13; a GaN amorphous layer 14 grown on the GaN nucleation layer 13; and a GaN thin film 15 grown on the GaN amorphous layer 14.

Figures 2 to 3 are the HRXRD spectra of the GaN thin film prepared in this embodiment. It can be seen from the X-ray swing curve that the half-maximum width (FWHM) value of the X-ray swing curve of GaN (0002) is lower than 0.2°. GaN(10-12) has a half-width value of 0.4°; it indicates that high-quality GaN films are epitaxially grown on ScMgAlO ₄ substrates.

The GaN thin film grown on the magnesium scandium aluminate substrate prepared in this example is used to prepare LED: on the GaN thin film grown on the magnesium scandium aluminate substrate prepared in this embodiment, Si-doped n Type silicon-doped GaN, In _x Ga _1-x N multi-quantum well layer, Mg-doped p-type magnesium-doped GaN layer, and finally electron beam evaporation to form ohmic contacts. The GaN-based LED device prepared on the magnesium scandium aluminate substrate has a thickness of n-type GaN of about 8 μm and a carrier concentration of 1×10 ¹⁹ cm ^-3 ; In _x Ga _{1- x} N/GaN The thickness of the multi-quantum well layer is about 240nm, and the number of periods is 15. Among them, the In _x Ga _1-x N well layer is 3nm, the GaN barrier layer is 13nm, and the thickness of the p-type magnesium-doped GaN layer is about 400nm. The concentration is 2×10 ¹⁷ cm ^-3 . Under the operating current of 20mA, the light output power of the LED device is 4.5mW, and the turn-on voltage value is 3V.

The GaN thin film grown on the magnesium scandium aluminate substrate prepared in this embodiment is used to prepare the MSM type ultraviolet photodetector: the GaN thin film grown on the magnesium scandium aluminate substrate prepared in this embodiment is sequentially subjected to light Engraving and development, electron beam evaporation deposition electrodes to form Schottky contacts, annealing and other processes. The thickness of the deposited electrode is about 80 μm, the annealing temperature is 500° C., and the annealing time is 180 s. Under the bias voltage of 10V, the dark current of the photodetector prepared in this example is only 9pA; and under the bias voltage of 3V, the maximum responsivity of the device at 365nm reaches 0.15A/W; the photoresponse increases from 10% to 90% in just 50ps.

Example 2

The preparation method of the GaN film grown on the magnesium scandium aluminate substrate comprises the following steps:

(1) Selection of the substrate and its crystal orientation: ScMgAlO ₄ substrate is used, with the (0001) plane offset by 0.5° to the (11-20) direction as the epitaxial plane, and the crystal epitaxial orientation relationship is: the (0001) plane of GaN is parallel to (0001) plane of ScMgAlO ₄ ;

(2) Substrate annealing treatment: the magnesium scandium aluminate substrate was annealed at 700°C for 2 hours in the molecular beam epitaxy vacuum growth chamber of the substrate to obtain an atomically flat surface;

(3) Epitaxial growth of GaN buffer layer: the substrate temperature is adjusted to 500°C, and pulsed laser deposition is used to grow 80nm-thick GaN buffer layer under the conditions of reaction chamber pressure of 3.0×10 ^-5 Pa and laser energy density of 2.0J/cm ² GaN buffer layer;

(4) Epitaxial growth of the GaN nucleation layer: the molecular beam epitaxy growth process was adopted, the substrate was kept at 600°C, the pressure of the reaction chamber was 8.0×10 ^-5 Pa, and the growth rate was 0.8ML/s. growing a GaN film with a thickness of 150 nm on the GaN buffer layer obtained in step (3);

(5) Growth of GaN amorphous layer: the molecular beam epitaxy growth process is adopted, the substrate is kept at 350°C, the pressure of the reaction chamber is 1.4×10 ^-4 Pa, and the growth rate is 0.6ML/s. (4) growing a GaN amorphous layer with a thickness of 50 nm on the obtained GaN nucleation layer to release the stress introduced during the growth;

(6) Epitaxial growth of GaN thin films: using the molecular beam epitaxy growth process, keeping the substrate at 500°C, under the conditions of the reaction chamber pressure of 8.0×10 ^-5 Pa and the growth rate of 0.8ML/s, in the step ( 5) A GaN thin film with a thickness of 400 nm is grown on the obtained GaN amorphous layer.

The GaN thin film on the magnesium scandium aluminate substrate prepared in this embodiment has very good optical properties, and the test data is similar to that of the embodiment 1, which will not be repeated here.

The above-mentioned embodiment is a preferred implementation mode of the present utility model, but the implementation mode of the present utility model is not limited by the described embodiment, and any other changes, modifications, modifications, Substitution, combination, and simplification should all be equivalent replacement methods, and are all included in the protection scope of the present utility model.

Claims (6)

1. The GaN thin film grown on the magnesium-scandium aluminate substrate is characterized in that it comprises a GaN buffer layer, a GaN nucleation layer, a GaN amorphous layer and a GaN thin film grown sequentially on the _ScMgAlO substrate. 2. The GaN thin film grown on the magnesium-scandium aluminate substrate according to claim 1, characterized in that, the _ScMgAlO substrate is epitaxial with the (0001) plane offset from the (11-20) plane by 0.5-1° noodle. 3 . The GaN film grown on a magnesium scandium aluminate substrate according to claim 1 , wherein the thickness of the GaN buffer layer is 30-80 nm. 4 . The GaN thin film grown on a magnesium scandium aluminate substrate according to claim 1 , wherein the GaN nucleation layer has a thickness of 50-150 nm. 5 . The GaN thin film grown on a magnesium scandium aluminate substrate according to claim 1 , wherein the GaN amorphous layer has a thickness of 10-120 nm. 6 . The GaN thin film grown on a magnesium scandium aluminate substrate according to claim 1 , wherein the GaN thin film has a thickness of 100-500 nm.