Structural and electronic properties of GeTe under pressure: ab initio study

The versatile phase transition character and associated intriguing electronic properties of germanium telluride (GeTe) have attracted intense interests from both academic and industrial perspectives. At ambient pressure, GeTe falls into a rhombohedral structure. With hydrostatic pressure applied, the rhombohedral R3mH GeTe transforms into NaCl (B1) structure at 3.2 GPa, and at 34.3 GPa, it transforms into CsCl (B2) structure. Diverse phase transitions under pressure lead to significant modulations in energy band gaps, which is still not clear. The aim of this research is to investigate the energy band gap of GeTe under pressure. Using first principles calculations, the proposed research investigates the structural phase transition and corresponding electronic energy band behaviour of GeTe under pressure. From the energy band structure analysis, it was found that the B2 phase is metallic, while the B1 and R3mH phases possess a narrow band gap at the equilibrium state. With pressure applied, the insulating gaps of both structures close gradually under positive pressure and enlarge upon negative pressure. The novel aspect of this work is the modulation of energy band gaps by mechanical pressure. The predicted band gaps can change over a wide range, which suggests possible and efficient electronic property modulation using external pressure. Furthermore, these findings are helpful in predicting the structural stability and optical band gap associated performance in GeTe based advanced materials under pressure.