For the first time, nanostructured thin films of the β-Ga2O3−GaN system have been obtained by plasma-enhanced chemical vapor deposition (PECVD) on c-plane sapphire substrates. High-purity gallium metal, as well as high-purity gaseous nitrogen and oxygen, were used as sources of macrocomponents. Low-temperature nonequilibrium plasma of an inductively coupled RF (40.68 MHz) discharge at reduced pressure (0.01 torr) was the initiator of chemical transformations between the reactants. A mixture of oxygen and nitrogen was used as a plasma-forming gas. The plasma-chemical process was studied using optical emission spectroscopy (OES). The resulting β-Ga2O3−GaN thin films with a GaN content of 2 to 7

The gas-sensitive properties of Ga2O3 films, first synthesized by plasma-enhanced chemical vapor deposition (PECVD), with respect to gaseous species of environmental and industrial interest were investigated in detail. The addition of some N2 during the PECVD process made it possible to reduce the inherent high resistance of Ga2O3 material and increase its gas sensitivity. The PECVD-Ga2O3 films demonstrated high responses to H2, O2 and NH3 with maximum response temperatures of 600 °C, 700 °C and 350 °C, correspondingly. The responses of Ga2O3 films to 1 vol. % of H2, 40 vol. % of O2 and 1 vol. % of NH3 at these temperatures were 400.73 %, 480.22 % and 335.35 %, correspondingly. The short response and recovery times of 7.6 s and 31.0 s have been achieved under H2 exposure. A plausible mechanism of the sensory effect of the PECVD-Ga2O3 films was suggested. Thus, the PECVD synthesized Ga2O3 films demonstrate a large potential for the development of high-speed performance H2 and O2 sensors working at high temperatures.

For the first time, nanostructured thin films of the β-Ga2O3−GaN system were obtained by plasma chemical deposition from the gas phase (PECVD) on c-sapphire substrates. High-purity metallic gallium, as well as high-purity gaseous nitrogen and oxygen were used as sources of macro components. The low-temperature nonequilibrium plasma of an inductively coupled HF (40.68 MHz) discharge at a reduced pressure (0.01 Torr) was the initiator of chemical transformations between the starting substances. A mixture of oxygen and nitrogen was used as a plasma-forming gas. The plasma chemical process was studied using the optical emission spectroscopy (OES) method. The obtained thin films of the β-Ga2O3−GaN system with a GaN phase content of 2 to 7% were characterized by various analytical methods.

The effect of the gaseous medium composition on the electrically conductive properties of In2O3–Ga2O3 films obtained by halide vapor phase epitaxy has been studied. In the temperature range of 100–550°C, the In2O3–Ga2O3 films exhibit high sensitivity to H2, NH3 and possess hyphen performance and low base resistance. A qualitative mechanism for the sensitivity of In2O3–Ga2O3 films to gases is proposed.

The effect of the gaseous medium composition on the electrically conductive properties of In 2 O 3 –Ga 2 O 3 films obtained by halide vapor phase epitaxy has been studied. In the temperature range of 100–550°C, the In 2 O 3 –Ga 2 O 3 films exhibit high sensitivity to H 2 , NH 3 and possess hyphen performance and low base resistance. A qualitative mechanism for the sensitivity of In 2 O 3 –Ga 2 O 3 films to gases is proposed.

The effect of H2, NH3, CO, CH4, O2 and NO2 on the electroconductive properties of the In2O3-Ga2O3 mixed compounds films obtained by the halide vapor phase epitaxy was studied. In the temperature range of 150-550 degrees C In2O3-Ga2O3 films are characterized by high responses, high speed of operation when exposed to H2, NH3, CO and O2. A qualitative mechanism of gas sensitivity for the In2O3-Ga2O3 mixed compounds films to gases was proposed. The gas-sensitive characteristics of In2O3, ic(e)-Ga2O3 and In2O3-Ga2O3 films were compared. The advantage of the In2O3-Ga2O3 mixed compounds films compared with Ga2O3 and In2O3 films is a low base electrical resistivity with a relatively high gas sensitivity.

The microstructure, composition, and electrical and gas-sensitive characteristics of sensors based on thin nanocrystalline SnO2 films with various catalysts deposited on the surface (Pt/Pd, Au) and introduced into the bulk (Au, Ni, Co) are investigated in the modes of constant and pulse heating. Atomic force microscopy and laser Raman spectroscopy are used to study micromorphology and structural defects depending on the composition of nanosized films. It is shown that sensors with Au and Co additives introduced into the volume make it possible to detect vapors of liquid hydrocarbons (on the example of aviation kerosene) at a concentration level of 5 ppm (0.1 of permissible exposure limit) and are characterized by increased stability of parameters during testing under prolonged exposure to vapors, as well as in conditions of varying humidity. Sensors with Au and Co additives in volume and deposited onto the film surface ultrathin two-layer Pt/Pd catalysts demonstrate the fastest response after testing.

The effect of the gaseous medium composition on the electrically conductive properties of In 2 O 3 -Ga 2 O 3 films obtained by halide vapor phase epitaxy has been studied. In the temperature range of 100-550 o C, the In 2 O 3 -Ga 2 O 3 films exhibit high sensitivity to H 2 , NH 3 and possess hyphen performance and low base resistance. A qualitative mechanism for the sensitivity of In 2 O 3 -Ga 2 O 3 films to gases is proposed. Keywords: In 2 O 3 -Ga 2 O 3 , halide vapor-phase epitaxy, gas sensitivity.

Gas sensing properties of Schottky metal-semiconductor-metal (MSM) structures based on alpha-Ga2O3 epitaxial films with Pt contacts are investigated. The electrical conductivity of the MSM structures exposed to H-2, O-2, CO, NO, CH4 and NH3 gases in the temperature range of 25-500 degrees C is studied. The structures show a very high sensitivity to H-2. It is found that Pt contacts and the Sn doping level play a key role in determining the hydrogen sensing properties of Pt/alpha-Ga2O3:Sn/Pt MSM structures. The sensitivity to H-2 is attributed to a modulation of the Schottky barrier height at the interface between Pt and alpha-Ga2O3:Sn.

The effect of the gaseous medium composition on the electrically conductive properties of In2O3-Ga2O3 films obtained by chloride vapor phase epitaxy has been studied. In the temperature range of 100-550ºC the In2O3 -Ga2O3 films exhibit high sensitivity to H2, NH3 and CO possessing high-speed performance and low-base-resistance. A qualitative mechanism for the sensitivity of In2O3-Ga2O3 films to gases is proposed.

The electrical and gas-sensitive characteristics of sensors based on thin nanocrystalline SnO2 films with various catalysts deposited on the surface (Pt/Pd, Au) and introduced into the bulk (Au, Ni, Co) are studied in the modes of constant and pulsed heating. Atomic force microscopy and laser Raman spectroscopy were used to study the micromorphology and structural defects depending on the composition of nanoscale films. it is shown that sensors with au and co additives introduced into the volume can detect liquid hydrocarbon vapors (for example, aviation kerosene) at a concentration level of 5 ppm (0.1 permissible exposure limit) and are characterized by increased stability of parameters during testing under prolonged exposure to vapors, as well as in conditions of changing humidity. Sensors with Au and Co additives in bulk and ultrathin Pt/Pd catalysts applied to the surface of the films are characterized by the highest performance after testing.

In this work, novel semiconductor sensors were developed for detecting high pre-explosive concentrations of H-2 (0.1-2.5 vol%) with high selectivity and stability. The sensors were based on thin (similar to 100 nm) nanocrystalline SnO2 films produced by magnetron sputtering of dispersed Pt and Pd layers deposited on the surface and addition of 13-14 at% Pt in the bulk. Studies on their nanostructure, composition, electrical properties, and gas-sensitive characteristics were carried out. X-ray photoelectron and Raman spectroscopies revealed that in the process of stabilizing annealing in Pt/Pd/SnO2:Sb,Pt film platinum introduced into the bulk segregates on the surface of the SnO2 microcrystals in the form of Pt degrees metal clusters and dispersed Pt2+ ions. The dispersed Pt2+ ions form bonds with lattice oxygen and contribute to the overlap of conduction channels. In the sensor subjected to annealing at T-an(1) = 723 K and T-an(2) = 873 K, the optimal situation is realized when under the action of low (n < 0.1 vol%) H-2 concentrations, the condition 2d(0) = d(M) is satisfied and G(1)/G(0) = 9-12. In the range of 0.1-2.5 vol% H-2, narrowing of the space-charge region favors the formation of a conducting layer, and at 2d(0) <= d(M) there is a sharp increase in the values of the responses to G(1)/G(0) = 220-250 at 2.5 vol%.

The effect of ambient humidity on the electrical conductive properties of α-Ga2O3 and α-Ga2O3/ε-Ga2O3 structures has been studied. Polymorphic Ga2O3 epitaxial layers were deposited by chloride vapor phase epitaxy on sapphire substrates. Pt and Pt/Ti were used as contacts. It was found that the Pt/α-Ga2O3/Pt and Pt/Ti/α-Ga2O3/ε-Ga2O3/Ti/Pt structures exhibit a high sensitivity of the current – voltage characteristics (I–V characteristics) to atmospheric humidity in the temperature range 25–100 °C. It was found that the effect of water vapor on the I–V characteristics of the structures is reversible and the most significant changes in the current in the samples are observed at a relative humidity RH ≥ 60%. With increasing temperature the effect of atmospheric humidity on the I–V characteristics decreases and disappears at T > 100 °C. The experimental results obtained are explained in terms of the Grottguss mechanism.

The effect of ambient humidity on the electrical conductivity of α-Ga2O3 and α-Ga2O3/ε-Ga2O3 is investigated. Polymorphic epitaxial Ga2O3 layers are deposited by the method of chloride vapor-phase epitaxy on sapphire substrates. The contacts are made of Pt and Pt/Ti. It is discovered that the I–V characteristics of the Pt/α-Ga2O3/Pt and Pt/Ti/α-Ga2O3/ε-Ga2O3/Ti/Pt structures have a high sensitivity to atmospheric humidity in the temperature range of 25–100°C. It is found that the effect of water vapor on the I–V characteristics is reversible, and the most significant current changes in the samples are observed at a relative humidity of RH ≥ 60%. As the temperature rises, the effect of atmospheric humidity on the I–V characteristics decreases and disappears at temperatures of T > 100°C. The experimental results obtained are explained within the framework of the Grotthuss mechanism.

The thin polycrystal Cr2O3 films were synthesized by RF - magnetron sputtering with followed annealing at T = 673 K in an air atmosphere. The grains diameter in the thin Cr2O3 film is 40–70 nm, Eg = 3.3±0.2 eV. In the temperature range of 303–473 K, the Cr2O3 films show high response to NO2, Н2, vapors of acetone and toluene, weakly react to CH4 and CO and have the relatively weak dependence of resistance on humidity. The qualitative model of the gases influences on the thin Cr2O3 films electrical properties was proposed.

The paper presents a comparison of the responses of sensors to ammonia in continuous heating and thermal cycling modes, and also shows the dependence of the response time of the sensors on the content NH3. Thin films of tin dioxide were obtained using RF magnetron sputtering, and then annealed in air at a temperature of 425 degrees C for 24 hours. In thermal cycling, the temperature of the heating cycle remains constant 400 degrees C (duration of the heating cycle was 8 s). The temperature of the cooling cycle changes in the range 200 degrees C - 100 degrees C, but duration of cooling of the cooling cycle was remained constant of 5 s. It was shown that the thermal cycling mode has several advantages over the constant heating mode. The experiments showed that sensors based on SnO2:Sb have short response times - less than 3 seconds.

The effect of temperature modulation on the response of ammonia sensors based on tin dioxide films was studied. Samples were obtained by RF-magnetron sputtering of a SnO2: Sb target on sapphire substrates with pre-deposited Pt-electrodes and a heater. Varying the duration of the heating cycle and lowering the temperature in the cooling cycle can increase the response by one to two orders of magnitude. The results are explained by a change in the density of chemically adsorbed oxygen on the surface of the SnO2: Sb film depending on the temperature mode.

Electrical characteristics of Metal/β-Ga2O3/n-Si structures with pure β-Ga2O3, Ti – and Cr – doped β-Ga2O3 films have been investigated. For all samples, regardless of the dopant type, a current decrease with the temperature increase is observed both at forward and reverse biases. The anomalous temperature dependencies are explained by the presence of traps located in a certain energy range near the bottom of the conduction band Ec. When the positive potential is applied to the electrode on the side of gallium oxide, the current-voltage characteristics are described as space charge limited current in the presence of energy distributed traps. In the case of a negative potential applied to the electrode on the side of gallium oxide, the reverse currents are due to the hopping conduction to the nearest neighboring state unoccupied by the electron.