Low-temperature non-metal-induced crystallization of germanium for fabrication of thin-film transistors

Device-quality poly-Ge layers were grown at temperatures as low as 200 °C by successive hydrogenation and annealing steps, with no need to any metal incorporation. Hydrogenation is performed in a PECVD apparatus with 150 W RF hydrogen plasma and annealing is carried out in the same system in N ₂ ambient. As a result, grains of the order of 100 nm are formed in the Ge layer. It has been observed that hydrogenation at high temperatures may be destructive to the Ge layer. Successive hydrogenation and annealing at respective temperatures of ISO and 200 °C would result in a device-quality poly crystalline Ge layer which has been employed for fabrication of depletion-mode thin-film transistors. These TFTs show a field-effect mobility of 80cm²/Vs for holes and an ON/OFF ratio of more than 10³, indicating the feasibility of this technique for applications in large-area electronics.