Ge-channel thin-film transistor with schottky Source/drain fabricated by low-temperature processing

The fabrication of Ge-channel thin-film transistors (TFTs) with Schottky source/drain (S/D) contacts was investigated. First, the annealing characteristics of Ni/c-Ge stacked structures were examined. NiGe/n-Ge Schottky contacts (Φ_Bn = 0.51 eV, n = 1) with a low reverse leakage current [(2-5) × 10^-2 A/cm²] were obtained at 200-300 °C. Second, the electrical characteristics of Al/SiO ₂/c-Ge metal-oxide-semiconductor (MOS) structures were investigated, in which SiO₂ films were formed by plasma-enhanced chemical vapor deposition at 250 °C. The MOS structures were proven acceptable for device operation. On the basis of the obtained results, TFTs with NiGe Schottky S/D contacts were fabricated using poly-Ge/quartz substrates. The maximum processing temperature was 500 °C in the solid-phase crystallization of a-Ge films. The TFTs showed good p-channel operation characteristics with a mobility of ∼ 100cm² V^-1 s^-1 without showing kink effects. This is a great advantage for the realization of high-performance TFTs for system-in-displays.