Synthesis of SnSe2 thin films by thermally induced phase transition in SnSe

Abstract

The synthesis of SnSe2 thin films, for phase change memory applications, generally require selenization and higher temperature. However, there are many critical problems associated with selenization, such as use of highly toxic H2Se/Se gas at high temperature, slow reaction rate and non-uniform composition of thin films. To overcome these problems, a novel and relatively low temperature synthesis of SnSe2 thin films has been reported here. Selenium rich Sn30Se70 (prepared by melt quenching technique) has been thermally evaporated in presence of Ar followed by vacuum annealing at 200 °C. An attempt has been made to elucidate the structural, optical and electrical properties of these thin films. X-ray diffraction and UV–Vis studies confirmed a phase change from orthorhombic SnSe to hexagonal SnSe2 followed by improvement in crystallinity (from ≈5 nm to 15 nm) and a red shift in optical band gap on annealing. Electrical studies revealed that SnSe phase have single thermal and photo activation energies in temperature range from −20 °C to 100 °C. A large contrast (four orders) in dark-conductivity [(3.19 ± 0.02) × 10−5Ω−1cm−1 to (5.16 ± 0.02) × 10−1Ω−1cm−1] between two phases of Sn30Se70, suggests its use in phase change memory devices. The SnSe2 phase is observed to be highly stable in the presence of visible light as compared to SnSe.