EFFECT OF COADSORPTION OF REDUCING GASES ON THE CONDUCTIVITY OF BETA-GA2O3 THIN-FILMS IN THE PRESENCE OF O2

The electrical conductivity of sputtered 2 mum thick films of the oxid e semiconductor beta-Ga2O3 was studied in function of the partial pres sure of CO or H-2 above the solid and also in the presence of CO+O2, H -2+O2 and CO + H-2 mixtures. The concentrations of the examined gases varied in the range 0.01-1 vol.% in nitrogen carrier gas, while the ex periments were carried out at 823, 873 and 923 K. Under the influence of H-2 and CO the conductivity of the samples increased with the parti al pressures of the gases according to the relations: lg sigma is simi lar to (1/n)lg p(CO) and lg sigma is similar to (l/m)lg p(H-2), where n and m are greater than unity. As a second step the effect of the coa dsorption of CO+O2 and H-2+O2 on the conductivity was investigated. Th e beta-Ga2O3 sensors, connected electrically by Pt electrodes, manifes ted a moderate catalytic activity. Due to this property the conductivi ty of the solid changed steeply in the vicinity of the stoichiometric composition of the gas mixtures. In the third step the coadsorption of CO+H-2 was studied. In function of the CO partial pressure the conduc tivity of the solid passed through a minimum. The shape of the experim ental curves was attributed to the formation of certain organic interm ediate surface compounds.