Method for preparing gallium oxide nanowire in low-concentration ozone atmosphere

Abstract

The invention relates to the technical field of semiconductors, and particularly discloses a method for preparing gallium oxide nanowires in a low-concentration ozone atmosphere, which comprises the following steps: selecting a c-plane sapphire substrate, and pretreating the c-plane sapphire substrate, namely performing ultrasonic cleaning by sequentially using acetone, absolute ethyl alcohol and deionized water, soaking the substrate in a mixed acid solution of 98% sulfuric acid and 85% phosphoric acid in a volume ratio of 3: 1 at 280 DEG C for 20 minutes, cleaning the substrate, and annealing the substrate in a nitrogen atmosphere for 2 hours to obtain a substrate with a flat surface and a step structure; transferring the pretreated substrate into a molecular beam epitaxy cavity, wherein the vacuum degree of the cavity reaches 1 * 10 <-9 > mbar; through combination of low-concentration ozone and the molecular beam epitaxy technology, the problem that a large amount of gaseous intermediate products are lost in a traditional method is avoided, the utilization efficiency of a gallium source and ozone is remarkably improved, meanwhile, additional growth of a buffer layer or introduction of a noble metal catalyst is not needed, the technological process is simplified, and the preparation cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and particularly relates to a method for preparing gallium oxide nanowires by using a low-concentration ozone atmosphere. Background Art

[0002] The new generation of ultra-wide bandgap semiconductor gallium oxide has the advantages of high breakdown electric field strength, good chemical and thermal stability, high Baliga figure of merit, etc., and has broad application prospects in fields such as deep ultraviolet photodetectors, high-power and high-voltage electronic devices. The specific surface area of nanowire materials is large, which is beneficial to enhancing the photoconductive effect of optoelectronic devices. Therefore, gallium oxide nanowires have greater application advantages in the optoelectronic field. Currently, the commonly used preparation technologies for gallium oxide nanowires include carbothermal reduction method, laser ablation technology, chemical vapor deposition technology, and catalyst-assisted growth technology.

[0003] In the above carbon reduction method, laser ablation method and CVD method, a large amount of gaseous intermediate products will be generated during the growth of nanowires. These intermediate products cannot be completely deposited on the substrate, and most of them will be lost with the carrier gas, which results in the problem of low utilization rate of reactants. For the catalyst-assisted growth method, it is necessary to additionally introduce metal nanoparticles as catalysts, such as noble metal Au, etc. This technology has the disadvantages of complex processes and high costs. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing gallium oxide nanowires by using a low-concentration ozone atmosphere to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for preparing gallium oxide nanowires by using a low-concentration ozone atmosphere, comprising:

[0007] S1. Select a c-plane sapphire substrate and perform pre-treatment on it, including sequentially ultrasonic cleaning with acetone, absolute ethanol and deionized water, then soaking in a mixed acid solution of 98% sulfuric acid and 85% phosphoric acid with a volume ratio of 3:1 at 280 °C for 20 min, and annealing in a nitrogen atmosphere for 2 h after cleaning to obtain a substrate with a flat surface and a stepped structure;

[0008] S2. Transfer the pre-treated substrate to a molecular beam epitaxy chamber, and the vacuum degree of the chamber reaches 1×10 - 9 mbar;

[0009] S3. Degas the substrate and verify the surface cleanliness and flatness by reflection high-energy electron diffraction;

[0010] S4. Heat the substrate to 500 °C, while raise the temperature of the gallium source to 860 °C, introduce ozone with a concentration of 6%, and adjust the chamber pressure to 2×10 -5 mbar, control the evaporation rate of the gallium source to be carry out the growth of gallium oxide nanowires;

[0011] S5. After the growth is completed, turn off the gallium source, keep the ozone atmosphere for in-situ annealing for 20 min, and characterize the sample after cooling.

[0012] Preferably, the purity of the nitrogen annealing in step S1 is 5N, and the gas flow rate is 20 SCCM.

[0013] Preferably, the ozone in step S4 is introduced through an improved gas delivery path, the gas path includes a mechanical pump, a vacuum gauge, a flow meter and a needle valve, and a metal extension tube is arranged in the chamber to increase the ozone concentration near the sample.

[0014] Preferably, the gallium source is a K-cell source, filled with 6N pure elemental gallium.

[0015] Preferably, during the growth process, the substrate temperature is controlled at 400 - 550 °C, and the ozone concentration and the pressure of the delivery pipeline are stabilized at 6% and 2000 Pa respectively.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] (1) By combining low-concentration ozone with molecular beam epitaxy technology, the problem of a large loss of gaseous intermediate products in the traditional method is avoided, the utilization efficiency of the gallium source and ozone is significantly improved, and at the same time, there is no need to grow an additional buffer layer or introduce a noble metal catalyst, simplifying the process flow and reducing the preparation cost.

[0018] (2) Using a 6N pure gallium source and an improved ozone delivery gas path to ensure the high purity of gallium oxide nanowires; by controlling the substrate temperature and ozone pressure, optimizing the surface mobility of gallium atoms and oxidation kinetics, realizing the uniform growth of nanowires with excellent crystallinity. Description of the Drawings

[0019] Figure 1 is the X-ray photoelectron spectroscopy image (narrow spectrum) of the comparative experimental example of the present invention;

[0020] Figure 2 is the photoelectron spectroscopy (full spectrum) of the comparative experimental example of the present invention;

[0021] Figure 3 is one of the scanning electron microscope images of the comparative experimental example of the present invention;

[0022] Figure 4 is the other scanning electron microscope image of the comparative experimental example of the present invention;

[0023] Figure 5 Atomic force microscope image of the comparative experimental example of the present invention;

[0024] Figure 6 X-ray diffraction image of the comparative experimental example of the present invention;

[0025] Figure 7 One of the energy-dispersive spectroscopy images (EDS) of the material of the present invention;

[0026] Figure 8 Another energy-dispersive spectroscopy image (EDS) of the material of the present invention;

[0027] Figure 9 Reflection high energy electron diffraction image of the present invention;

[0028] Figure 10 Schematic diagram of the experimental system of the present invention. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] Embodiment 1:

[0031] Please refer to Figures 1-10 As shown, a method for preparing gallium oxide nanowires using a low-concentration ozone atmosphere includes:

[0032] S1. Place the c-plane sapphire substrate in acetone, absolute ethanol, and deionized water in sequence for ultrasonic cleaning for 30 minutes each to remove surface organic matters and impurities;

[0033] After drying the substrate with high-purity nitrogen, immerse it in a mixed acid solution of 98% sulfuric acid (H2SO4) and 85% phosphoric acid (H3PO4) with a volume ratio of 3:1, and treat it at a constant temperature of 280°C for 20 minutes to remove surface residual pollutants and form a regular step structure. Thoroughly rinse the substrate with deionized water, dry it with nitrogen, place it in a quartz boat, transfer it to a tube furnace, and anneal it at 1000°C for 2 hours in an atmosphere of 5N purity nitrogen (flow rate 20 SCCM). After annealing, characterize it by atomic force microscope (AFM) to confirm that the surface is flat and has a clear step structure;

[0034] S2. Transfer the pretreated substrate to a molecular beam epitaxy (MBE) growth chamber through a rapid injection chamber. The vacuum degree of the rapid injection chamber needs to reach 1×10-8 mbar, the initial vacuum degree of the molecular beam epitaxy cavity reaches 1×10 -9 mbar, and the substrate is slowly heated for degassing treatment (heating rate 5℃ / min) to avoid pressure fluctuations in the cavity caused by the violent desorption of adsorbed water molecules or impurities.

[0035] S3. After the cavity is stable, use reflection high-energy electron diffraction (RHEED) to verify the cleanliness of the substrate surface. After confirming no contamination, raise the substrate temperature to 500℃; turn on the gallium source and raise the gallium source temperature to 860℃, and set the gallium evaporation rate to

[0036] Start the ozone generator, adjust the ozone concentration to 6%, the pressure of the delivery pipeline to 2000 Pa, and ensure the stable delivery of ozone to the sample surface through an improved delivery gas path (including a mechanical pump, a needle valve, and a metal extension tube). The working pressure of the cavity is maintained at 2×10 -5 mbar, open the gallium source baffle, and start the growth of gallium oxide nanowires for a duration of 60 min;

[0037] S4. After the growth is completed, close the gallium source baffle, keep the ozone pressure unchanged, and perform in-situ annealing at 500℃ for 20 min to optimize the crystallinity of the nanowires. After cooling to room temperature, compare the diffraction patterns before and after growth by RHEED. A clear striped diffraction pattern is observed, indicating the ordered growth of the nanowires along a specific crystal orientation. Transfer the sample to an X-ray photoelectron spectroscopy (XPS) instrument for composition analysis. The results show that the binding energy of the Ga2p 3 / 2 peak is 1118.2 eV, and the binding energy of the O1 s peak is 531.2 eV, which is consistent with the binding energy positions of gallium and oxygen elements in β-Ga2O3, confirming that the composition of the nanowires is gallium oxide. Observed by scanning electron microscopy (SEM), the diameter of the nanowires is 30 - 50 nm, the length reaches hundreds of nanometers, and they are evenly distributed on the substrate surface.

[0038] Comparative experimental example: Influence of substrate temperature on the morphology of gallium oxide

[0039] The experimental conditions are set as follows: Except for the substrate temperature, the other parameters are the same as those in Example 1 (550℃), specifically including: ozone concentration: 6%; gallium source temperature: 860℃; gallium evaporation rate: Cavity pressure: 2×10 -5 mbar; the substrate temperature is set to four groups of 400℃, 450℃, 500℃, and 550℃ (other parameters are the same as those in Example 1).

[0040] In the experiment of the experimental group (400 °C), during the growth process, RHEED showed that the diffraction spots gradually transformed into a blurred ring pattern, indicating the formation of an amorphous or microcrystalline thin film. SEM characterization showed that the substrate surface was a continuous and dense gallium oxide thin film without a nanowire structure. XPS analysis showed that the oxygen vacancy concentration increased by 15% compared with Example 1. It is speculated that the kinetic energy of the gallium-oxygen reaction at low temperature is insufficient to form the droplet autocatalytic conditions required for nanowires;

[0041] In the experiment of the experimental group (450 °C), some of the RHEED fringes were retained, but the intensity decreased, indicating an increase in surface roughness; SEM showed that sparse short nanowires coexisted with the thin film; the XPS oxygen vacancy concentration decreased to 8%, and the Ga / O atomic ratio was close to 1:1.28. The increase in temperature promoted the partial migration of gallium atoms, but did not reach the threshold for stable nucleation of droplets, resulting in the mixed growth of nanowires and thin films;

[0042] In the experiment of the experimental group (500 °C), during the growth process, the RHEED fringes were clear, indicating an improvement in surface order. SEM showed uniformly distributed nanowires; TEM showed that the nanowires were single-crystalline β-Ga2O3; the XPS oxygen vacancy concentration was further reduced to 5%, and the Ga / O atomic ratio was 1:1.40; the temperature was close to the optimal range, and the migration rate of gallium atoms matched the droplet stability, realizing the preferential growth of nanowires;

[0043] In the experimental procedure of the experimental group (550 °C), during the growth process, the RHEED fringes were sharp and the periodicity was obvious, indicating a highly ordered surface structure. SEM showed no obvious nanowire structure and no thin film existed; XPS also did not detect the signal of gallium element. Instead, only the signals of aluminum and oxygen were seen; at 550 °C, due to the too high temperature, gallium atoms and oxygen were activated and preferentially formed gallium suboxides and were rapidly desorbed, resulting in no gallium oxide left on the substrate surface. This shows that it is difficult to prepare gallium oxide nanowires at too high temperatures.

[0044] As can be seen from the above, the substrate temperature needs to be controlled within the range of 400 - 550 °C, and 500 °C is the optimal value. Too low a temperature will lead to the formation of a thin film or incomplete reaction, while too high a temperature will inhibit the growth of nanowires.

[0045] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing gallium oxide nanowires using a low-concentration ozone atmosphere, characterized in that, Including: S1. Select a c-plane sapphire substrate and perform pre-treatment on it, including ultrasonic cleaning successively with acetone, absolute ethanol and deionized water, then soaking it in a mixed acid solution of 98% sulfuric acid and 85% phosphoric acid with a volume ratio of 3:1 at 280 °C for 20 min, and annealing it in a nitrogen atmosphere for 2 h after cleaning to obtain a substrate with a flat surface and a stepped structure; S2. Transfer the preprocessed substrate into a molecular beam epitaxy chamber, and the vacuum degree of the chamber reaches 1×10 -9 mbar; S3. Degas the substrate and verify the surface cleanliness and flatness by reflection high energy electron diffraction; S4. Heat the substrate to 500 °C, while heating the gallium source temperature to 860 °C, and introduce ozone with a concentration of 6%, adjust the chamber pressure to 2×10 -5 mbar, control the evaporation rate of the gallium source to be for the growth of gallium oxide nanowires; S5. After the growth is completed, turn off the gallium source, maintain the ozone atmosphere for in-situ annealing for 20 min, and characterize the sample after cooling.

2. The method for preparing gallium oxide nanowires using a low-concentration ozone atmosphere according to claim 1, wherein: In the step S1, the purity of the nitrogen annealing is 5N and the gas flow rate is 20 SCCM.

3. A method for preparing gallium oxide nanowires using a low-concentration ozone atmosphere according to claim 1, characterized in that: In the step S4, ozone is introduced through an improved gas delivery path, and the gas path includes a mechanical pump, a vacuum gauge, a flow meter and a needle valve, and a metal extension tube is arranged in the cavity to increase the ozone concentration near the sample.

4. A method for preparing gallium oxide nanowires using a low-concentration ozone atmosphere according to claim 1, characterized in that: The gallium source is a K-cell source filled with 6N pure elemental gallium.

5. A method for preparing gallium oxide nanowires using a low-concentration ozone atmosphere according to claim 1, characterized in that: During the growth process, the substrate temperature is controlled at 400 - 550 °C, and the ozone concentration and the pressure of the delivery pipeline are stabilized at 6% and 2000 Pa respectively.

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