Sensing characteristics of hematite and barium oxide doped hematite films towards ozone and nitrogen dioxide

Hematite (α-Fe2O3) and barium oxide doped hematite (BaO-Fe2O3) thin films were investigated as ozone (O3) and nitrogen dioxide (NO2) sensing materials. Fe2O3 and BaO-Fe2O3 films were deposited by radio- frequency sputtering using pure Fe2O3, and 1-2% BaO doped Fe2O3 targets. The 700 °C (1 hour) annealed films showed significant responses to O3 at temperatures ranging from 150 °C to 300 °C. Although, hematite is an n-type semiconductor, the Fe2O3 and BaO-Fe2O3 films exhibit p-type behavior to O3 and n- type behavior to NO2 at the studied concentration ranges in this work. The response to oxidizing gases is not strictly an increase in resistance due to a conversion from n-type to p-type depending on gas concentrations. This effect is more visible with increasing Ba concentration.