A study of surface modification at semiconducting Ga2O3 thin film sensors for enhancement of the sensitivity and selectivity

N-type semiconducting Ga2O3 thin films which are stable at high temperatures are being used as a new basic material for gas sensors. This study is an attempt to determine to what extent coating the surface of Ga2O3 thin films with another metal oxide will produce new gas sensitivities. The process involves sputtering a modification layer which is typically 30-300 nm thick onto a readily prepared planar Ga2O3 sensor with a film thickness of 2 mu m Ta2O5, WO3, NiO and AlVO4 were used to form the modification layer. It was found that in some cases there was a radical change in gas sensitivity characteristics especially with WO3, NiO and AlVO4. The observed effects depend strongly on annealing and operating temperature. These results are the basis for sensors which react sensitively to NO and NH3, for selective O-2 sensors, for Ga2O3 sensors which react to reducing gases with the same sign of conducting change as p-type semiconductors and a gas-sensitive reference element.