Effect of heat treatment on the electronic properties of vacuum-deposited In–Se films

Chalcogenide semiconductors, mainly composed of S, Se, and Te, exhibit a variety of physical properties due to their unique electronic structure. In particular, their thermoelectric properties, phase-change phenomena, and electrical switching properties make them promising materials for next-generation electronic devices. However, the electronic properties of systems containing amorphous components remain unclear. In particular, there is a strong need to understand the defect states in the band gap that affect the performance of electronic devices. Therefore, we focus on In–Se based materials, which are representative binary chalcogenide materials, and attempt experimental observation of the defect states that exist in these materials. The optical and electrical properties of mixture films of In and Se with the composition ratio of 0.31:0.69 prepared by vacuum deposition were investigated after heat treatment up to 300 °C. The band gap energy increased with heat treatment, from ~ 0.88 to ~ 1.42 eV, and the electrical resistivity at room temperature changed from 4.4 × 10⁵ to 2.4 × 10⁰ Ω·m. The changes in structure and defect absorption due to heat treatment were evaluated by X-ray diffraction and photothermal deflection spectroscopy. Based on these experimental results, band models including localized states and their application to electronic devices are discussed.