Thermodynamic and optoelectronic properties of ultra-thin-film crystalline and amorphous selenium from a first-principles investigation

Selenium is a vital earth-abundant and non-toxic material that has been used for many practical applications for decades. Both experimental and theoretical investigations are going on the different selenium phases across the scientific communities for understanding its thermodynamic, electronic, and optical properties. However, stabilizing the amorphous phase of it and the role of various defects in crystalline (c-Se) and amorphous (a-Se) phases still warrant rigorous studies. In this case, the first-principles based calculations can provide a robust understanding of how crystalline to amorphous phase transition occurs and pinpoints a practical route to stabilize it in the amorphous phase for its most promising application as a photo-sensitive material for efficient photodetection technologies. We present our density functional theory (DFT) based investigations for both c-Se and a-Se, focusing on the thermodynamic and optoelectronic properties in this work. Our ab initio molecular dynamics studies reproduce the experimentally observed structural properties of a-Se. DFT studies on (100) surface of trigonal selenium show promising optical properties compared to the pure bulk phase's optical properties.