Yu. S. Petrova

Ga 2 O 3 Films Formed by Electrochemical Oxidation

The effect of oxygen plasma on gallium oxide films formed by electrochemical oxidation of n-GaAs wafers with a donor concentration Nd = (1–2) × 1016 cm−3 has been investigated. It is shown that the treatment in an oxygen plasma at a temperature of 50–90°C increases the concentration of β-phase crystallites, which causes an increase in the permittivity, a decrease in the dielectric dissipation factor, and a change in the conductivity of GaAs-〈gallium oxide〉-metal structures.

Effect of thermal annealing and exposure to oxygen plasma on the properties of TiO2-Si structures

The effect of thermal annealing and exposure to oxygen plasma on the phase composition, structure, and microprofile of titanium-dioxide films deposited by high-frequency magnetron sputtering on silicon substrates is studied. The influence exerted by processing modes on the capacitance-voltage and conductance-voltage characteristics of Me-TiO2-Si-Me structures and on the density of surface states at the semiconductor-insulator interface is examined. It is shown that TiO2 films are amorphous upon their fabrication. Upon the annealing of films at 500°C in an argon atmosphere, crystallites of anatase and rutile appear in the amorphous matrix. The treatment of a titanium-dioxide film in oxygen plasma gives rise to rutile crystallites with new crystallographic planes. As a result of annealing at 750°C, the anatase phase disappears and the film becomes polycrystalline, containing only rutile crystallites. The capacitance of Me-TiO2-Si-Me structures in the accumulation mode reaches the maximum value upon annealing at 750°C, which is due to the transformation of titanium dioxide to the rutile phase. The specific capacitance is 5.9 × 10−2 F/cm3. The decrease in the capacitance of the structures and in the amount of fixed charge in the insulator upon exposure to oxygen plasma is due to the diffusion of oxygen atoms across the titanium-dioxide layer to give a SiO2 film at the TiO2-Si interface. As a result of the annealing and treatment of a titanium-dioxide film in oxygen plasma, the energy density of surface states decreases by more than an order of magnitude as compared with the unannealed samples.

Effect of oxygen plasma on the properties of tantalum oxide films

The effect of oxygen plasma on the leakage current, permittivity, and the dielectric loss tangent of Ta2O5 thin layers (300–400 nm) is studied. It is suggested to treat tantalum oxide films in oxygen plasma to control their electrical and dielectric characteristics.

Gallium-oxide films obtained by thermal evaporation

The current-voltage (I–V), capacitance-voltage (C–V), and conductance-voltage (G–V) characteristics of metal/GaxOy/GaAs/metal structures are investigated. Gallium-oxide films with a thickness of 150–170 nm are deposited by the thermal evaporation of Ga2O3 powder onto n-type GaAs substrates with the donor concentration Nd = 2 × 1016 cm−3. Treatment of the GaxOy films in oxygen plasma causes a decrease in both the forward and reverse currents and a shift of the C–V and G–V curves to higher positive voltages. The Fermi level at the insulator/semiconductor interface in the structures under study is unpinned. The density of states at the GaxOy/GaAs interface is Nt = (2–6) × 1012 eV−1 cm−2.

Photoelectric characteristics of metal-Ga2O3-GaAs structures

We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga2O3-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga2O3 crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga2O3 crystallites and become transparent. Under illumination of the Ga2O3-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga2O3 film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga2O3-GaAs interface and in the Ga2O3 film.

Photoelectric characteristics of metal-Ga{sub 2}O{sub 3}-GaAs structures

We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga2O3-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga2O3 crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga2O3 crystallites and become transparent. Under illumination of the Ga2O3-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga2O3 film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga2O3-GaAs interface and in the Ga2O3 film.

Properties of TiO2 films on silicon substrate

Influence of the substrate material and the effect of oxygen plasma on the microprofile and electrical properties of TiO2 films deposited by radio-frequency magnetron sputtering are studied. It is shown that the most continuous films with the smallest roughness are obtained when deposited onto silicon substrates. The change in the capacitance-voltage and conductance-voltage characteristics of the structures upon their exposure to oxygen plasma is accounted for by the diffusion of oxygen atoms across the titanium-dioxide film and by the appearance of a SiO2 layer at the Si-TiO2 interface.

Electrical characteristics of n-GaAs-anode film-Ga2O3-metal structures

The influence of oxygen plasma and thermal annealing at 900°C on the capacitance-voltage and conductivity-voltage characteristics of n-GaAs-(anodic oxide)-metal structures is studied. In contrast to the unannealed structures, high-temperature annealing in Ar for 30 min leads to the emergence of a voltage dependence of the capacitance (C) and conductivity (G). The influence of oxygen plasma on a Ga2O3 film before annealing promotes additional variation in the capacitance-voltage and conductivity-voltage characteristics.

Deep centers in TiO2-Si structures

The effects of thermal annealing and exposure to oxygen plasma on the electrical and photoelectric properties of metal-TiO2-Si structures are investigated. The TiO2 films are fabricated by the rf magnetron sputtering of a titanium-oxide target onto unheated n-Si substrates. The forward and reverse currents of the structures after annealing in argon at 500°C are lower than those after annealing at 750°C. Exposure of the titanium-dioxide films to oxygen plasma led to a decrease in the currents at all annealing temperatures. It is supposed that the I–V characteristics of the TiO2-Si structures can be described using the model of space-charge-limited currents. The photoelectric characteristics of the samples are investigated via illumination at a wavelength of λ = 400 nm. The TiO2-Si structures annealed at 500°C without exposure to oxygen plasma exhibit frozen photoconductivity. The relaxation time is 23 ± 2 min.

Effect of annealing in argon on the properties of thermally deposited gallium-oxide films

The effect of the annealing temperature on the I–V, C–I, and G–V characteristics and transparency of gallium-oxide films is investigated. The films are fabricated by the thermal evaporation of Ga2O3 powder on n-GaAs wafers. It is shown that the films which are amorphous after deposition crystallize upon annealing at temperatures Tan ≥ 800°C. The electrical characteristics and photoresponse of the V/Ni-GaAs-GaAs-GaxOy-V/Ni samples to visible radiation depend on the structure and phase composition of the films.