High oxygen sensitivity of TiO2 thin films deposited by ALD

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

Effect of oxygen on the electrical conductivity of Pt-contacted α-Ga2O2/ε(κ)-Ga2O3 MSM structures on patterned sapphire substrates

Electrical conductivity and gas sensitivity of α-Ga2O2/ ε(κ)-Ga2O3 structures were measured for oxygen concentrations ranging from 2 % to 100 % and temperatures ranging from 25 °C to 220 °C. It was found that the oxygen sensitivity of the structures depended on the donor dopant concentration. The alpha -Ga _{2}O_{3}/arepsilon ( kappa )-Ga 2 O 3 structures doped with sim 1.5 imes 10^{17} cm −3 of Sn showed high sensitivity to O 2 in the temperature range from 180 °C to 220 °C and at the bias voltage below 7.5 V. This effect can be attributed to the chemisorption of oxygen molecules on the surface of structures, which reduces energy barriers between ε(κ)-Ga2O3 grains

Low-resistivity gas sensors based on the In2O3-Ga2O3 mixed compounds films

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 °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, κ(ε)-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

HVPE growth of corundum-structured α-Ga2O3 on sapphire substrates with α-Cr2O3 buffer layer

Gallium oxide films were grown by HVPE on (0001) sapphire substrates with and without α-Cr2O3 buffer produced by RF magnetron sputtering. Deposition on bare sapphire substrates resulted in a mixture of α-Ga2O3 and ε-Ga2O3 phases with a dislocation density of about 2∙1010 cm-2. The insertion of α-Cr2O3 buffer layers resulted in phase-pure α-Ga2O3 films and a fourfold reduction of the dislocation density to 5∙109 cm-2

ITO Thin Films for Low-Resistance Gas Sensors

This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP08856540). The research was carried out with the support of a grant under the Decree of the Government of the Russian Federation No. 220 of 9 April 2010 (Agreement No. 075-15-2022-1132 of 1 July 2022). In addition, this research was partly performed at the Institute of Solid State Physics, University of Latvia (ISSP UL). ISSP UL, as the Centre of Excellence, has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD01-2016-2017-Teaming Phase2 under Grant Agreement No. 739508, project CAMART2.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. © 2022 by the authors. --//-- Published under the CC BY 4.0 license.Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP08856540); ISSP UL, as the Centre of Excellence, has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD01-2016-2017-Teaming Phase2 under Grant Agreement No. 739508, project CAMART2

Ion implantation in β-Ga2O3 : Physics and technology

Gallium oxide, and in particular its thermodynamically stable β-Ga2O3 phase, is within the most exciting materials in research and technology nowadays due to its unique properties. The very high breakdown electric field and the figure of merit rivaled only by diamond have tremendous potential for the next generation “green” electronics enabling efficient distribution, use, and conversion of electrical energy. Ion implantation is a traditional technological method used in these fields, and its well-known advantages can contribute greatly to the rapid development of physics and technology of Ga2O3-based materials and devices. Here, the status of ion implantation in β-Ga2O3 nowadays is reviewed. Attention is mainly paid to the results of experimental study of damage under ion irradiation and the properties of Ga2O3 layers doped by ion implantation. The results of ab initio theoretical calculations of the impurities and defect parameters are briefly presented, and the physical principles of a number of analytical methods used to study implanted gallium oxide layers are highlighted. The use of ion implantation in the development of Ga2O3-based devices, such as metal oxide field-effect transistors, Schottky barrier diodes, and solar-blind UV detectors, is described together with systematical analysis of the achieved values of their characteristics. Finally, the most important challenges to be overcome in this field of science and technology are discussed

Oxygen sensors based on gallium oxide thin films with addition of chromium

This article reveals the gas-sensitive properties of polycrystalline gallium oxide thin films with chromium additives. Incorporation of the Cr2O3 phase into the β-phase gallium oxide film structure leads to the Ga2O3 grain size decrease. The oxygen-sensitivity of the gallium oxide films appears at 300 C. The oxygen increases reversibly the sensor resistance due to an increase in the height of the energy band bending at the Ga2O3 grain boundary with the chemisorption of atomic O. The chromium oxide formed in the Ga2O3 films stimulated dissociative adsorption of the oxygen due to its high catalytic activity via a spill-over mechanism. The temperature range of 500–700 C appears to be the most efficient for the oxygen detection in the concentration range from 9 to 100 vol%. The response time of the sensor was 20 s at 700 C in an initial nitrogen- containing atmosphere at О2 exposure to 21 vol% and the recovery time comprised 52 s. Meantime, the sensors did not practically react to a gas reducing and high humidity

Influence of electrodes on the parameters of solar-blind detectors of UV radiation

The influence of the topology of electrodes on the electrical and photoelectric characteristics of metal–semiconductor–metal structures is studied. Gallium-oxide films are produced by the radio-frequency magnetron-assisted sputtering of a Ga2O3 target onto (0001)-oriented sapphire substrates. Two types of electrodes are formed on the surface of the oxide films. The first type corresponded to two parallel electrodes spaced by an interelectrode distance of 250 μm, and the second type to interdigitated electrodes. In the case of the second type of electrodes, the distance between the “fingers” is 50, 30, 10, and 5 μm. The structures possess sensitivity to ultraviolet radiation at a wavelength of λ = 254 nm, irrespective of the type of contact. The second type of detectors with an interelectrode distance of 5 μm show the largest photocurrents, Iph = 3.8 mA, and a specific detectivity of D* = 5.54 × 1015 cm Hz0.5 W–1

Electrical conductive and photoelectrical properties of heterostructures based on gallium and chromium oxides with corundum structure

α-Ga2O3/α-Cr2O3 heterostructures with a corundum structure were obtained by chloride vapor phase epitaxy and magnetron sputtering. The structural, electrical conductive and photoelectrical properties of the obtained samples were studied. It was established that the α-Ga2O3/α-Cr2O3 heterostructures exhibits weak rectifying properties and in comparison with α-Ga2O3 films has a higher response speed when exposed to ultraviolet radiatio

Investigation of the persistence conductivity and photoelectric characteristics in detectors with interdigital electrodes based on β-Ga2O3

Herein, the electrical and photoelectric characteristics of solar-blind UV detectors based on β-Ga2O3 films with interdigital electrodes are presented. The sensors with interdigital electrodes have interelectrode spacing d = 5, 10, 30, and 50 μm. The structures exhibit high sensitivity to ultraviolet radiation with a wavelength of λ = 254 nm. The detectors with the smallest interelectrode spacing (5 μm) demonstrate the highest photocurrent value. The detectors have a saturation region on the current–voltage characteristics under UV irradiation, which shifts to the region of lower voltages with decreasing interelectrode spacing. A mechanism to explain the presence of the saturation region on the I–V characteristic is proposed. The sensors exhibit high value of a persistence photoconductivity, which decreases exponentially with an estimated value of the time constant t 1 = 59–63 s