66 ISSN 0020-1685, Inorganic Materials, 2020, Vol. 56, No. 1, pp. 66–71. © Pleiades Publishing, Ltd., 2020. Russian Text © The Author(s), 2020, published in Neorganicheskie Materialy, 2020, Vol. 56, No. 1, pp. 69–75. Gas-Sensing Properties of Thin Films Grown on the Surface of InP Single Crystals by Thermal Oxidation V. F. Kostryukov a, *, I. Ya. Mittova a , and Saud Ali a a Voronezh State University, Universitetskaya pl. 1, Voronezh, 394006 Russia *e-mail: vc@chem.vsu.ru Received April 17, 2018; revised July 11, 2019; accepted August 6, 2019 Abstract—Thin nanofilms have been grown on the surface of single-crystal InP wafers using PbO + V 2 O 5 mixtures in the gas phase. The oxide mixtures used as chemical stimulators have been shown to accelerate the thermal oxidation of InP. The resultant films exhibit gas-sensing properties for ammonia (concentration of 140 ppm) and carbon monoxide (95 ppm). The highest gas sensitivity is near 1.2 arb. units, at temperatures in the range 200–240°C. Keywords: semiconductors, indium phosphide, thermal oxidation, thin films, gas sensitivity DOI: 10.1134/S0020168520010070 INTRODUCTION Chemical gas sensors based on nanocrystalline metal oxide semiconductors are currently the most promising solid-state gas detectors because they offer high reliability and are easy to fabricate. Tin dioxide- based gas-sensing films have been manufactured for a rather long time and possess satisfactory characteris- tics [1–4]. Nevertheless, there is an ongoing search for new materials suitable as basic components of semicon- ductor gas sensors. At present, research effort is con- centrated on oxides such as In 2 O 3 , ZnO, and Ga 2 O 3 . In 2 O 3 possesses high sensitivity, fast response, a con- venient working resistivity range, and a rather low temperature for detection of oxidizing and reducing gases in air. There is ample evidence that the high sur- face oxygen mobility characteristic of indium oxide plays a decisive role in its exceptional gas-sensing properties. Its gas-sensing response is due to an adsorption competition mechanism: oxygen displace- ment from the surface and subsequent adsorption of gas molecules of interest on active In 2 O 3 centers [5– 11]. Not only thin films of undoped indium oxide but also those doped with various metals can be used as a gas-sensing layer, which improves the selectivity and stability of the sensor material. One way of producing thin semiconductor films on semiconductor surfaces is chemically stimulated ther- mal oxidation [12]. The use of additional com- pounds—chemical stimulators—in semiconductor oxidation processes makes it possible to simultane- ously accelerate the film growth process on the semi- conductor surface and dope the film. This approach to the preparation of thin gas-sensing layers was shown to be very effective in the case of GaAs [13, 14]. The chemically stimulated thermal oxidation of semicon- ductors with the participation of oxide compounds has a number of advantages: the possibility of doping thin films directly during the film growth process (with variations in both the dopant and doping level); the simple procedure, and, as a consequence, relatively cheap apparatus; and the short time needed for obtaining the desired material. The purpose of this work was to grow gas-sensing nanofilms on the surface of InP in the presence of a mixture of PbO and V 2 O 5 as chemical stimulators. EXPERIMENTAL We studied thin films grown on the surface of indium phosphide wafers (FIEO, 100 orientation, 300-K concentration of majority carriers no lower than 5 × 10 16 cm –3 , intrinsic n-type conductivity) in the presence of PbO + V 2 O 5 mixtures in the gas phase. InP was oxidized at 500 and 550°C for 10, 20, 30, 40, 50, and 60 min at a constant oxygen f low rate of 30 L/h in a 30-mm-diameter horizontal quartz reactor placed in an MTP-2M-50-500 furnace. Prior to thermal oxi- dation, the InP wafers were pretreated in an etchant with the composition H 2 SO 4 (reagent grade, Russian Federation State Standard GOST 4204-77, 92.80%) : H 2 O 2 (extrapure grade, Russian Federation Purity Standard TU 6-02-570-750, 56%) : H 2 O = 2 : 1 : 1. The etching time was 10 min. Next, the wafers were rinsed repeatedly in distilled water and dried in air. The temperature in the reactor was maintained con- stant (±1°C) by a TPM-10 meter/controller. The