Detection of oxygen vacancy defect states in oxide nanobelts by using thermally stimulated current spectroscopy

Photoconducting properties of individual single crystalline Sn3O4 nanobelts were investigated by performing transport measurements. The nanobelts were found to exhibit large responsivity under ultraviolet (UV) illumination: the electric current in one single nanobelt greatly increases by about three orders of magnitude. Such photoconductive behavior was ascribed to the photogeneration of electron-hole pairs and to surface effects such as the oxidation and photoreduction of oxygen molecules (trapping). These mechanisms were found to be drastically modulated by the presence of oxygen vacancies which generates additional energy states that provide free electrons for conduction in our samples. In fact, we report the use of the thermally stimulated current spectroscopy as a powerful tool to study the presence of additional energy levels on Sn3O4 nanobelts as an approach to apply this technique in any high-resistivity nanomaterial. The experimental data provided two vacancy-related levels in 0.01 and 0.2 eV. On the basis of the transport measurements, a qualitative model to explain the response of these samples to UV light is proposed.