Ammonia sensitivity of rf sputtered tellurium oxide thin films

In this work we present the results of a study concerning the sensitivity properties of tellurium oxide (TeO2) thin films to ammonia gas. TeO2 films were grown on quartz substrates by means of the rf reactive sputtering method using a tellurium target in an Ar–O2 atmosphere with different O2/Ar ratio ranging from 35/65 to 50/50. The structure, surface morphology and chemical composition of the prepared films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The energy gap Eg of the films was evaluated from transmission (T) and reflection (R) spectra. To characterize the films as sensors, experiments with ammonia (NH3) at concentration levels of 100–500 ppm and at operating temperatures ranging from 130 to 220 °C were performed. The films deposited with a O2/Ar ratio of 45/55 and thermally treated at 450 °C for 60 min were polycrystalline and showed satisfactory response to NH3 at the optimum operating temperature of 170 °C. At this temperature the response and recovery times were about 3.1 and 5.6 min, respectively. The sensitivity of the TeO2 films follows a power law relationship with the increase of the gas concentration.