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The gas sensitivity and structural properties of TiO2 thin films deposited by plasma-enhanced atomic layer deposition (ALD) were examined in detail. The TiO2 thin films are deposited using Tetrakis(dimethylamido)titanium(IV) and oxygen plasma at 300 °C on SiO2 substrates followed by annealing at temperatures of 800 °C. Gas sensitivity under exposure to O2 within the temperature range from 30 °C to 700 °C was studied. The ALD-deposited TiO2 thin films demonstrated high responses to O2 in the dynamic range from 0.1 to 100 vol. % and low concentrations of H2, NO2. The ALD deposition allowed the enhancement of sensitivity of TiO2 thin films to gases. The greatest response of TiO2 thin films to O2 was observed at a temperature of 500 °C and was 41.5 arb. un. under exposure to 10 vol. % of O2. The responses of TiO2 thin films to 0.1 vol. % of H2 and 7 × 10–4 vol. % of NO2 at a temperature of 500 °C were 10.49 arb. un. and 10.79 arb. un., correspondingly. The resistance of the films increased due to the chemisorption of oxygen molecules on their surface that decreased the thickness of the conduction channel between the metal contacts. It was suggested that there are two types of adsorption centers on the TiO2 thin films surface: oxygen is chemisorbed in the form of O2– on the first one and O– on the second one.

Indium tin oxide thin films were deposited by magnetron sputtering on ceramic aluminum nitride substrates and were annealed at temperatures of 500 °C and 600 °C. The structural, optical, electrically conductive and gas-sensitive properties of indium tin oxide thin films were studied. The possibility of developing sensors with low nominal resistance and relatively high sensitivity to gases was shown. The resistance of indium tin oxide thin films annealed at 500 °C in pure dry air did not exceed 350 Ohms and dropped by about 2 times when increasing the annealing temperature to 100 °C. Indium tin oxide thin films annealed at 500 °C were characterized by high sensitivity to gases. The maximum responses to 2000 ppm hydrogen, 1000 ppm ammonia and 100 ppm nitrogen dioxide for these films were 2.21 arbitrary units, 2.39 arbitrary units and 2.14 arbitrary units at operating temperatures of 400 °C, 350 °C and 350 °C, respectively. These films were characterized by short response and recovery times. The drift of indium tin oxide thin-film gas-sensitive characteristics during cyclic exposure to reducing gases did not exceed 1%. A qualitative model of the sensory effect is proposed.

A method was developed for plasma-enhanced chemical vapor deposition of β-Ga2O3:Zn thin films with the possibility of pre-purifying precursors. The structural and electrically conductive properties of β-Ga2O3:Zn thin films were studied. Increasing the temperature of the Zn source (TZn) to 220 °C led to the formation of Ga2O3 films with a Zn concentration of 4 at.%, at TZn = 230 °C [Zn] = 6 at.% and at 235 °C. [Zn] = 8 at.% At TZn = 23 °C, the films corresponded to the β-Ga2O3 phase and were single-crystalline with a surface orientation of (–201). As TZn increased, the polycrystalline structure of β-Ga2O3 films with a predominant orientation of (111) was formed. The introduction of Zn led to the formation of a more developed microrelief of the surface. Raman spectroscopy showed that a small concentration of impurity atoms tended to replace gallium atoms in the oxide lattice, which was also confirmed by the Hall measurements. The concentration of charge carriers upon the introduction of Zn, which is a deep acceptor, decreased by 2–3 orders of magnitude, which mainly determined the decrease in the films’ resistivity. The resulting thin films were promising for the development of high-resistivity areas of β-Ga2O3-based devices.

Vertical Schottky barrier diodes based on an ion beam sputter (IBS)-deposited β-Ga2O3 film on a single-crystalline (2¯01) unintentionally doped (UID) β-Ga2O3 with a Ni contact were developed. To form ohmic Ti/Ni contacts, the IBS-Ga2O3/UID β-Ga2O3 structures were wet-etched, and an indium tin oxide (ITO) intermediate semiconductor layer (ISL) was deposited on the opposite surface of the UID β-Ga2O3. The IBS-deposited Ga2O3 layer was polycrystalline and semi-insulating. Low leakage currents, rectification ratios of 3.9 × 108 arb. un. and 3.4 × 106 arb. un., ideality factors of 1.43 and 1.24, Schottky barrier heights of 1.80 eV and 1.67 eV as well as breakdown voltages of 134 V and 180 V were achieved for diodes without and with ITO-ISL, respectively. The surface area of the IBS-Ga2O3 film acted as a thin dielectric layer and, together with the preliminary wet etching, provided low leakage currents and relatively high Schottky barrier heights. Diodes with a Schottky barrier based on a Ni/IBS-deposited Ga2O3 film contact were demonstrated for the first time.

The use of CH4 as an energy source is increasing every day. To increase the efficiency of CH4 combustion and ensure that the equipment meets ecological requirements, it is necessary to measure the CH4 concentration in the exhaust gases of combustion systems. To this end, sensors are required that can withstand extreme operating conditions, including temperatures of at least 600 °C, as well as high pressure and gas flow rate. ZnGa2O4, being an ultra-wide bandgap semiconductor with high chemical and thermal stability, is a promising material for such sensors. The synthesis and investigation of the structural and CH4 sensing properties of ceramic pellets made from pure and Er-doped ZnGa2O4 were conducted. Doping with Er leads to the formation of a secondary Er3Ga5O12 phase and an increase in the active surface area. This structural change significantly enhanced the CH4 response, demonstrating an 11.1-fold improvement at a concentration of 104 ppm. At the optimal response temperature of 650 °C, the Er-doped ZnGa2O4 exhibited responses of 2.91 a.u. and 20.74 a.u. to 100 ppm and 104 ppm of CH4, respectively. The Er-doped material is notable for its broad dynamic range for CH4 concentrations (from 100 to 20,000 ppm), low sensitivity to humidity variations within the 30–70% relative humidity range, and robust stability under cyclic gas exposure. In addition to CH4, the sensitivity of Er-doped ZnGa2O4 to other gases at a temperature of 650 °C was investigated. The samples showed strong responses to C2H4, C3H8, C4H10, NO2, and H2, which, at gas concentrations of 100 ppm, were higher than the response to CH4 by a factor of 2.41, 2.75, 3.09, 1.16, and 1.64, respectively. The study proposes a plausible mechanism explaining the sensing effect of Er-doped ZnGa2O4 and discusses its potential for developing high-temperature CH4 sensors for applications such as combustion monitoring systems and determining the ideal fuel/air mixture.

Introducing other elements into gallium oxide materials to modify their properties is a hot topic today. This paper attempts to introduce Bi element to prepare (Bi x Ga 1-x ) 2 O 3 alloy semiconductor thin film by radio frequency co-sputtering, so as to achieve precise and effective tuning of its band gap. The sputtering power of Ga 2 O 3 target remains constant at 80 W. The content of Bi element in the material is adjusted by varying the sputtering power of the Bi 2 O 3 target. Samples with different Bi doping concentrations were obtained after annealing at 800 °C for 2 h. Fortunately, (Bi x Ga 1-x ) 2 O 3 semiconductor alloy films were successfully prepared by radio frequency co-sputtering, and the optical energy gap could be adjusted approximately linearly in the range of 5.14 to 5.27 eV by varying the Bi content. X-ray diffraction and scanning electron microscope results show that a phase transition occurs in the material when the sputtering power of Bi 2 O 3 is 40 W. The results of Urbach energy and film transmittance indicate that moderate Bi doping can reduce the disorder of the material structure and improve the transmittance of the film. However, excessive Bi doping introduces more defects, increasing the scattering and absorption of the defects, ultimately leading to a reduction in film transmittance. These findings have propelled research in the field of gallium oxide doping and its band gap modulation.

Vertical Schottky barrier diodes based on an ion beam sputter (IBS)-deposited β-Ga[sub.2] O[sub.3] film on a single-crystalline (2¯01) unintentionally doped (UID) β-Ga[sub.2] O[sub.3] with a Ni contact were developed. To form ohmic Ti/Ni contacts, the IBS-Ga[sub.2] O[sub.3] /UID β-Ga[sub.2] O[sub.3] structures were wet-etched, and an indium tin oxide (ITO) intermediate semiconductor layer (ISL) was deposited on the opposite surface of the UID β-Ga[sub.2] O[sub.3] . The IBS-deposited Ga[sub.2] O[sub.3] layer was polycrystalline and semi-insulating. Low leakage currents, rectification ratios of 3.9 × 10[sup.8] arb. un. and 3.4 × 10[sup.6] arb. un., ideality factors of 1.43 and 1.24, Schottky barrier heights of 1.80 eV and 1.67 eV as well as breakdown voltages of 134 V and 180 V were achieved for diodes without and with ITO-ISL, respectively. The surface area of the IBS-Ga[sub.2] O[sub.3] film acted as a thin dielectric layer and, together with the preliminary wet etching, provided low leakage currents and relatively high Schottky barrier heights. Diodes with a Schottky barrier based on a Ni/IBS-deposited Ga[sub.2] O[sub.3] film contact were demonstrated for the first time.

TiO2 films of 130 nm and 463 nm in thickness were deposited by ion beam sputter deposition (IBSD), followed by annealing at temperatures of 800 °C and 1000 °C. The effect of H2, CO, CO2, NO2, NO, CH4 and O2 on the electrically conductive properties of annealed TiO2 thin films in the operating temperature range of 200–750 °C were studied. The prospects of IBSD deposited TiO2 thin films in the development of high operating temperature and high stability O2 sensors were investigated. TiO2 films with a thickness of 130 nm and annealed at 800 °C demonstrated the highest response to O2, of 7.5 arb.un. when exposed to 40 vol. %. An increase in the annealing temperature of up to 1000 °C at the same film thickness made it possible to reduce the response and recovery by 2 times, due to changes in the microstructure of the film surface. The films demonstrated high sensitivity to H2 and nitrogen oxides at an operating temperature of 600 °C. The possibility of controlling the responses to different gases by varying the conditions of their annealing and thicknesses was shown. A feasible mechanism for the sensory effect in the IBSD TiO2 thin films was proposed and discussed.

The paper presents the results of an investigation of the nanostructure, elements, and phase composition of thin (100–140 nm) tin dioxide films obtained via magnetron sputtering and containing Ag, Y, Sc, Ag + Y, and Ag + Sc additives in the volume. Electrical and gas‐sensitive characteristics of hydrogen sensors based on these films with dispersed Pt/Pd layers deposited on the surface were studied. The additives had a significant effect on the nanostructure of the films, the density of oxygen adsorption sites on the surface of tin dioxide, the band bending at the grain boundaries of tin dioxide, the resistance values in pure air, and the responses to hydrogen in the concentration range of 50–2000 ppm. During the long‐term tests of most of the samples studied, there was an increase in the resistance of the sensors in clean air and in the response to hydrogen. It has been established that the joint introduction of Ag + Y into the volume of films prevents the increase in the resistance and response. For these sensors based on thin films of Pt/Pd/SnO2:Sb, Ag, Y the responses to 100 and 1000 ppm of H2 are 25 and 575, correspondingly, the response time at exposure to 100 and 1000 ppm of H2 are 10 and 90 s, the recovery time at exposure to 100 and 1000 ppm of H2 17 and 125 s. Possible mechanisms of the effect of additives on the properties of sensors and the stability of their parameters during long‐term operation were considered.

A method was developed for plasma-enhanced chemical vapor deposition of β-Ga O :Zn thin films with the possibility of pre-purifying precursors. The structural and electrically conductive properties of β-Ga O :Zn thin films were studied. Increasing the temperature of the Zn source ( ) to 220 °C led to the formation of Ga O films with a Zn concentration of 4 at.%, at = 230 °C [Zn] = 6 at.% and at 235 °C. [Zn] = 8 at.% At = 23 °C, the films corresponded to the β-Ga O phase and were single-crystalline with a surface orientation of (-201). As increased, the polycrystalline structure of β-Ga O films with a predominant orientation of (111) was formed. The introduction of Zn led to the formation of a more developed microrelief of the surface. Raman spectroscopy showed that a small concentration of impurity atoms tended to replace gallium atoms in the oxide lattice, which was also confirmed by the Hall measurements. The concentration of charge carriers upon the introduction of Zn, which is a deep acceptor, decreased by 2-3 orders of magnitude, which mainly determined the decrease in the films' resistivity. The resulting thin films were promising for the development of high-resistivity areas of β-Ga O -based devices.