Germanium telluride (GeTe) is a p-type V-VI compound semiconductor. GeTe has a large number of Ge vacancies, which generate a large number of hole carriers. These hole carriers give GeTe high electrical conductivity. At the same time, it can be observed that the high electronic thermal conductivity stems from the high electrical conductivity, thus increasing the total thermal conductivity. Due to the good physicochemical properties, GeTe is mainly used as a thermoelectric and semiconductor material for the fabrication of high-performance semiconductor films, low-temperature superconductors, and nanomaterials.

GeTe has a chlorite and rock salt structure and crystallises in the trigonal R3m space group.Ge2? bonds with six equivalent Te2- atoms to form a mixture of corner-sharing and edge-sharing GeTe? octahedra. The tilt angle of the corner-sharing octahedron is 12°. There are three shorter (2.81 ?) and three longer (3.30 ?) Ge-Te bond lengths. Te2- is bonded to six equivalent Ge2? atoms to form a mixture of corner-sharing and edge-sharing TeGe? octahedra. The tilt angle of the corner-sharing octahedron is 12°.

GeTe has two structures, α and β, and undergoes a phase transition from the α-phase to the β-phase at 700 K. The β-phase is a cubic phase structure at high temperatures. For GeTe system, the β-phase at high temperature is a cubic phase structure, and its energy band degeneracy is higher than that of the α-phase at room temperature. If the phase transition temperature is lowered, the β-phase structure can be obtained in a milder temperature range while maintaining good thermoelectric properties.

References:

[1] LUO YUE; Pengpeng B, SHUQI ZHENG*;  Doping Copper Selenide for Tuning the Crystal Structure and Thermoelectric Performance of Germanium Telluride-Based Materials[J]. ACS Applied Materials & Interfaces, 2023. DOI:10.1021/acsami.2c21002.