HALL-COEFFICIENT MEASUREMENTS FOR SNO2 DOPED SENSORS, AS A FUNCTION OF TEMPERATURE AND ATMOSPHERE

The Hall coefficient has been measured for thin (300 nm) r.f. sputtered Al, In-doped SnO2 and undoped SnO2 films. Two experiments have been carried out: (i) Hall measurements in a temperature range of 20 to 300-degrees-C in inert (Ar), reductor (H-2 0.2%) and oxidant (O2 2%) atmospheres. Aged films were also tested in Ar. (ii) Hall measurements as a function of H-2 (0-2%) and O2 (0-20%) concentrations at fixed temperature. Conduction mechanisms were discussed adjusting temperature dependent results to a grain boundary carried-trapping model. A grain size dependent sensitivity model has been used to explain H-2 and O2 sensitivities. Combining results from both models, we are able to establish the best conditions for detection of reductor and oxidant gases.