Metal-to-insulator transition induced by UV illumination in a single SnO nanobelt.

An individual tin oxide (SnO) nanobelt was connected in a back-gate field-effect transistor configuration and the conductivity of the nanobelt was measured at different temperatures from 400 K to 4 K, in darkness and under UV illumination. In darkness, the SnO nanobelts showed semiconductor behavior for the whole temperature range measured. However, when subjected to UV illumination the photoinduced carriers were high enough to lead to a metal-to-insulator transition (MIT), near room temperature, at T  = 240 K. By measuring the current versus gate voltage curves, and considering the electrostatic properties of a non-ideal conductor, for the SnO nanobelt on top of a gate-oxide substrate, we estimated the capacitance per unit length, the mobility and the density of carriers. In darkness, the density was estimated to be 5-10 × 10 cm, in agreement with our previously reported result (Phys. Status Solid. RRL 6, 262-4 (2012)). However, under UV illumination the density of carriers was estimated to be 0.2-3.8 × 10 cm near T , which exceeded the critical Mott density estimated to be 2.8 × 10 cm above 240 K. These results showed that the electrical properties of the SnO nanobelts can be drastically modified and easily tuned from semiconducting to metallic states as a function of temperature and light.