Gas sensors based on pseudohexagonal phase of gallium oxide

The electrical conductivity of pseudohexagonal ε(κ)-Ga2O3 films under different ambient gases (H2, NO2, O2, and CO) is studied in a range of temperatures from 400 to 550 °C. The exposure of ε(κ)-Ga2O3 to reducing gases such as H2 and CO results in a reversible increase in current and conductance. The exposure to the oxidizing gases such as NO2 and O2 has the opposite effect. The maximum response to reducing gases (H2 and CO) is observed at 500 °C and to oxidizing gases at 550 and 450 °C for NO2 and O2, respectively. The highest sensitivity to H2 is achieved at low applied voltages (≤7.9 V). In contrast, the highest sensitivity to NO2 is observed at high applied voltages. The response and recovery times and temporal drift of ε(κ)-Ga2O3 characteristics under different ambient are estimated. Polycrystalline ε(κ)-Ga2O3 exhibits the semiconducting mechanism of electron transport at high temperatures. A qualitative model of the gas-sensing effect based on the modulation of electron concentration near the surface region of ε(κ)-Ga2O3 due to the chemisorption of gas molecules is described. Tin doping of ε(κ)-Ga2O3 increases the response to H2 at the temperature range from 25 to 550 °C