Deep-level transient spectroscopy at platinum/titanium-dioxide hydrogen sensors

Abstract

Abstractauthoren Deep traps in platinum/mesoporous-titanium-dioxide hydrogen sensors are studied by deep-level transient spectroscopy (DLTS) before, during, and after the gas detection. This is possible for atmospheric hydrogen volume fractions in the low ppm regime where the Schottky barrier at the Pt/TiO2 interface is retained. In the absence of hydrogen, two deep levels with binding energies of 470 and 720 meV are found. Their occurrence increases as hydrogen is offered, but to a smaller extent than the hydrogen-induced doping density. An additional level develops during hydrogen exposure at a binding energy of ≈870meV. After the sensing sequence, the sample recovers only partially, but the deep trap densities can be reset by annealing in dry air. The data suggest that besides donor formation, exposure of mesoporous TiO2 to hydrogen also generates deep traps. The results furthermore show that despite the large interfacial disorder, which in the present case is essential for the functionality, DLTS can be used to obtain information about deep traps generated during utilization of the device as gas sensor.