CN114717657A - A method for growing nickel oxide single crystal thin films based on plasma-assisted laser molecular beam epitaxy - Google Patents

Abstract

The invention discloses a method for growing a nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy. First, the oxide substrate is pretreated; then, oxygen plasma-assisted laser molecular beam epitaxy is used to heteroepitaxially grow nickel oxide on the oxide substrate at room temperature to obtain single crystal nickel oxide. The invention combines substrate pretreatment and oxygen plasma assisted deposition, optimizes growth conditions through laser molecular beam epitaxy, obtains NiO single crystal at normal temperature, improves crystal quality, reduces surface roughness, and improves device performance increase is more substantial. Benefiting from the effective pretreatment of the substrate, a macroscopic step flow structure is formed on the surface of the substrate, which is conducive to the formation of NiO single crystals; in addition, oxygen atoms are activated with the assistance of oxygen plasma, and heteroepitaxial single crystals are formed at room temperature. Crystalline NiO. The high-quality heteroepitaxy of this natural p-type material on gallium oxide substrates broadens the avenues for the realization of gallium oxide-based high-power devices.

Description

Method for growing nickel oxide single crystal thin films based on plasma-assisted laser molecular beam epitaxy

technical field

The invention relates to a method for growing a nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy, and belongs to the technical field of wide-bandgap semiconductor material device preparation.

Background technique

As an ultra-wide bandgap semiconductor material, Ga ₂ O ₃ has a large band gap (4.5–4.9eV) and high breakdown field strength (8MV/cm), and its Baliga figure of merit exceeds 3000, which is a wide band gap. It is 5-10 times that of semiconductor GaN and SiC, and has broad application prospects in the fields of power devices and radio frequency devices. However, there are still many challenges in _Ga2O3 research, and the lack of p _- type doping capability is still the main limitation of _{Ga2O3 -} based power electronic devices. Exploring other p-type wide-bandgap semiconductor materials and forming high _- quality heterointegration with _Ga2O3 is a possible solution.

NiO, a natural p-type oxide semiconductor, has attracted much attention due to its band gap of 3.2–3.8 eV, excellent chemical stability, and high visible light transmittance. In addition, the large exciton binding energy (110 meV) makes it more widely used than GaN, ZnO, etc., and there is a well _- matched epitaxial relationship and energy band structure between NiO and _Ga2O3 . Commonly used nickel oxide epitaxy methods include magnetron sputtering, laser molecular beam epitaxy, and the like. The nickel oxide obtained by magnetron sputtering is usually polycrystalline and amorphous. The surface roughness of the film obtained by this particle bombardment deposition method is relatively large, and there are various defects in the crystal. The existence of polygrain boundaries also hinders the transfer of carriers. Transport, so that there is still a big limit to the improvement of device performance.

At present, in order to obtain a heteroepitaxial thin film of a high-quality oxide, high-temperature epitaxy is often required, and the epitaxy cost is high and the process is complicated. In addition, the commonly used growth methods such as magnetron sputtering are often particle bombardment deposition rather than epitaxial growth, and polycrystalline and amorphous nickel oxides are usually obtained. The surface roughness is large and the crystal quality is poor, so that there is still a bottleneck in the improvement of device performance. .

SUMMARY OF THE INVENTION

The purpose of the invention is: aiming at improving the quality of nickel oxide crystal and breaking through the bottleneck of device performance, it is proposed to combine substrate pretreatment and oxygen plasma assisted deposition to obtain nickel oxide with low surface roughness by laser molecular beam epitaxy (LMBE) at room temperature single crystal method. The oxygen plasma-assisted NiO growth in the present invention does not require high temperature, simplifies the growth steps, and optimizes the pretreatment of the substrate and the growth conditions so that the common polycrystalline and amorphous products are optimized to single crystal NiO, and the crystal quality is improved. , which reduces the surface roughness and improves the device performance even more.

The present invention adopts the following technical solutions for solving the above-mentioned technical problems:

Based on the method for growing nickel oxide single crystal thin film by plasma-assisted laser molecular beam epitaxy, combined with substrate pretreatment and oxygen plasma assistance, nickel oxide single crystal is obtained by laser molecular beam epitaxy at room temperature, which specifically includes the following steps:

(1) Pretreatment of the oxide substrate;

(2) Using oxygen plasma-assisted laser molecular beam epitaxy, at room temperature, heteroepitaxial nickel oxide is obtained on an oxide substrate to obtain single crystal nickel oxide.

Further, the oxide substrate in step (1) is c-plane sapphire, ZnO or Ga ₂ O ₃ .

Further, the specific steps of the pretreatment in step (1) are: etching the oxide substrate in hot concentrated sulfuric acid for 0.5-1 h, and then annealing at high temperature for 12-24 h.

Further, the temperature of the concentrated sulfuric acid is 120-180°C.

Further, the annealing temperature is 1000-1500°C.

Further, in step (2), the laser wavelength is λ=248 nm, the laser power density is 135-225 mJ, and the laser frequency is 1-10 Hz.

Further, the oxygen plasma power in step (2) is 150-300W, the oxygen flow rate is 1.5-3 sccm, and the growth pressure is 1×10 ^-5 -9×10 ^-5 Torr.

Further, the specific steps of the heteroepitaxial nickel oxide on the oxide substrate described in step (2) are:

Put the cleaned and nitrogen blown substrate into the pre-extraction chamber of the laser molecular beam epitaxy equipment, and then send it to the growth chamber after baking and degassing in the pre-extraction chamber; the target is nickel oxide, and the growth atmosphere is O ₂ .

Further, the vacuum degree of the pre-pumping chamber is below 6×10 ^-7 Torr, and the background vacuum degree of the growth chamber is below 6×10 ^-8 Torr; the distance d _ST between the substrate and the target is 40～ 50cm; the purity of the O ₂ is above 99.99%, and the purity of the nickel oxide target is above 99.99%.

In the nickel oxide single crystal film prepared according to the method, the surface roughness of the nickel oxide single crystal film is reduced to 0.20 nm.

beneficial effect

(1) Combined with substrate pretreatment, oxygen plasma assistance, and optimization of growth conditions, NiO single crystals were obtained at room temperature by laser molecular beam epitaxy, and the surface roughness could be reduced to 0.20 nm.

(2) Thanks to the effective pretreatment of the substrate, the surface of the substrate is formed, which is beneficial to the formation of NiO single crystal; the oxygen plasma-assisted deposition activates the oxygen atoms, enabling heteroepitaxial NiO single crystal at room temperature.

In short, the NiO obtained by heteroepitaxial is single crystal, and the surface roughness is greatly reduced.

Description of drawings

Figure 1 is a reflection high-energy electron diffraction pattern of NiO obtained by room temperature epitaxy on a c-plane sapphire substrate.

Figure 2 is an X-ray 2θ–ω scan of NiO obtained by room temperature epitaxy on a c-plane sapphire substrate.

FIG. 3 is a rocking curve diagram of the X-ray diffraction (111) plane of the prepared NiO thin film.

Figure 4(a) is the atomic force microscope image of the pretreated c-plane sapphire substrate, and (b) is the atomic force microscope image of the prepared NiO single crystal thin film.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, but not to be construed as a limitation of the present invention.

The oxide substrates used for NiO heteroepitaxy are c-plane sapphire, ZnO, Ga ₂ O ₃ .

Example 1

This embodiment is to carry out the epitaxy of nickel oxide single crystal at room temperature with the help of oxygen plasma on a sapphire substrate, and the specific steps are as follows:

(1) Pretreatment of the c-plane sapphire substrate: etching in hot concentrated sulfuric acid (150°C) for 30min, and annealing at high temperature (1200°C) in an annealing furnace for 12h;

(2) Using laser molecular beam epitaxy (λ=248nm), heteroepitaxial NiO at room temperature: put the cleaned and nitrogen-drying substrate into the pre-extraction chamber of the laser molecular beam epitaxy equipment, and the vacuum of the pre-extraction chamber The vacuum degree is 6×10 ^-7 Torr, and it is sent to the growth chamber after being baked and degassed in the pre-extraction chamber. The background vacuum degree of the growth chamber is 6×10 ^-8 Torr; the target material is NiO (purity 99.99%). ), the growth atmosphere is O ₂ (purity above 99.99%); the substrate-target spacing d _ST is 45cm, the laser power density is 135mJ, and the laser frequency is 2Hz;

(3) With the aid of oxygen plasma assisted deposition, the oxygen plasma power is 200W, the oxygen flow rate is 2sccm, and the growth pressure is 6×10 ^-5 Torr. The NiO epitaxy is carried out at room temperature, and the growth time is 3h.

Figure 1 shows the reflection high-energy electron diffraction pattern of NiO obtained by room temperature epitaxy on a c-plane sapphire substrate. From the diffraction fringes in the figure, it can be seen that the prepared NiO is a single crystal, and the surface of the sample is very flat.

Figure 2 shows the X-ray 2θ–ω scan of NiO obtained by room temperature epitaxy on a c-plane sapphire substrate. It can be seen from the figure that the diffraction peak of NiO is cubic NiO, confirming that the obtained heteroepitaxy is Cubic NiO single crystal.

Figure 3 is the rocking curve diagram of the X-ray diffraction (111) surface of the prepared NiO thin film, the half-height width of the rocking curve is an important indicator to characterize the quality of the single crystal, and the half-height of the rocking curve of the prepared NiO thin film (111) surface The width is 0.77°, indicating that the prepared NiO single crystal thin film has good crystal quality.

Figure 4(a) is the atomic force microscope image of the pretreated c-plane sapphire substrate. From the figure, we can see the grooves and the surface roughness is 0.23nm; (b) is the atomic force microscope image of the prepared NiO thin film, The surface roughness was 0.20 nm.

Claims (10)

1. the method for growing nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy, is characterized in that, in conjunction with substrate pretreatment and oxygen plasma assistance, single crystal nickel oxide is obtained by laser molecular beam epitaxy at normal temperature, specifically including The following steps: (1) Pretreatment of the oxide substrate; (2) Using oxygen plasma-assisted laser molecular beam epitaxy, at room temperature, heteroepitaxial nickel oxide is obtained on an oxide substrate to obtain single crystal nickel oxide. 2 . The method for growing nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy according to claim 1 , wherein the oxide substrate in step (1) is c-plane sapphire, ZnO or Ga ₂ O ₃ . . 3. The method for growing nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy according to claim 1, wherein the specific step of the pretreatment in step (1) is: placing the oxide substrate in a hot concentrated Corrosion in sulfuric acid for 0.5~1h, and then high temperature annealing for 12~24h. 4 . The method for growing a nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy according to claim 3 , wherein the temperature of the concentrated sulfuric acid is 120-180° C. 5 . 5 . The method for growing a nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy according to claim 3 , wherein the annealing temperature is 1000-1500° C. 6 . 6 . The method for growing nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy according to claim 1 , wherein the laser wavelength in step (2) is λ=248 nm or 193 nm, and the laser power density is 135～135 nm. 7 . 225mJ; laser frequency is 1～10Hz. 7. The method for growing nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy according to claim 1, wherein the oxygen plasma power in step (2) is 150-300W, and the oxygen flow rate is 1.5-3sccm , the growth pressure is 1×10 ^-5 to 9×10 ^-5 Torr. 8. The method for growing nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy according to claim 1, wherein the specific step of heteroepitaxial nickel oxide on the oxide substrate in step (2) is: : Put the cleaned and nitrogen blown substrate into the pre-extraction chamber of the laser molecular beam epitaxy equipment, and then send it to the growth chamber after baking and degassing in the pre-extraction chamber; the target is nickel oxide, and the growth atmosphere is O ₂ . 9 . The method for growing a nickel oxide single crystal thin film based on plasma-assisted laser molecular beam epitaxy according to claim 8 , wherein the vacuum degree of the pre-pumping chamber is below 6×10 ⁻⁷ Torr, and the actual value of the growth chamber is less than 6×10 −7 Torr. 10 . The bottom vacuum degree is below 6×10 ^{- 8} Torr; the distance d _ST between the substrate and the target material is 40-50cm; the purity of the O ₂ is above 99.99%, and the purity of the nickel oxide target material is above 99.99% . 10. The nickel oxide single crystal thin film prepared according to any one of claims 1-9, wherein the surface roughness of the nickel oxide single crystal thin film is reduced to 0.20 nm.

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