Abstract
Oxygen and ozone responses on the 
and 
diodes were measured at low temperature (30–100°C). Large responses to oxygen and ozone were observed for the former diode, but only an oxygen response was observed for the latter diode. The Schottky barrier height, φ, determined from the measured photocurrent‐bias curve, decreased with increases in oxygen and ozone concentrations for the 
diode, but increased with an increase in oxygen concentration for the 
diode. Surface redox mechanisms were proposed for the responses of these diodes, where the following equations held
for oxygen
for ozone The experimental values were compared to the theoretical values from the slopes of 
in the above equations. The response time of the diode is discussed together with the surface condition of the semiconducting oxide and the role of the metal as a catalyst.