High-Temperature Defect-Induced Hopping Conduction in Multilayered Germanium Sulfide for Optoelectronic Applications in Harsh Environments

Intrinsic crystal defects play a major role in tailoring the electrical and optical properties of two-dimensional (2D) materials. Here, we probe the impact of planar crystal defects on the electrical characteristics of germanium sulfide (GeS) field effect transistor (FET) at different operating temperatures varying from 300 to 575 K. Our results show that the measured mobility of the GeS field effect transistor was 0.04 × 10^-3 cm²/(V s) at 300 K, and this value reached 58 × 10^-3 cm²/(V s) at 575 K. It is important to note that the mobility of GeS FET at elevated temperatures in this study is greater than the mobilities in the recently reported GeS photodetector studies. Furthermore, evidence that the threshold voltage (V_th) decreases and carrier concentration increases with increasing temperature in the GeS channel is provided. We demonstrate an Arrhenius-like relation of the carrier transport as a function of temperature, a behavior that we attribute to nearest-neighbor-hopping (NNH) conduction. The existence of planar defects is revealed using transmission electron microscopy (TEM) while density functional theory (DFT) analysis supports the hypothesis that the formation of localized energy states governs hopping conduction. This study reports hopping conduction at the temperature above 300 K for the first time, whereas previous investigations on 2D materials have reported a hopping mechanism in the low-temperature (<200 K) range. These observations give insight into the fundamental charge conduction mechanisms at high temperature in other 2D materials systems which are expected to aid in the development of applications for harsh environments.