Synthesis, Crystal Growth, and Transport Properties of van der Waals Tetrel Pnictide GeAs2

Bulk GeAs2 was synthesized utilizing a vapor transport reaction with iodine. Thermal stability tests under dynamic conditions show that GeAs2 decomposes below 700 K, in contrast to the reported congruent melting at 1029 K measured at saturated As vapor pressure. GeAs2 is a p-type narrow bandgap (similar to 0.4 eV) semiconductor. From a thermoelectric standpoint, GeAs2 outperforms previous computational predictions in thermopower and thermal conductivity. However, electrical resistivity is significantly higher than predicted values, resulting in the low overall thermoelectric figure of merit. Aliovalent doping strategies for GeAs2 should be developed to achieve reasonable thermoelectric performance.