Amorphous Silicon and Silicon-Germanium Thin-Film Transistors Formed by Ion Implantation

Thin-film, n-channel transistors were fabricated in hydrogenated amorphous silicon and silicongermanium thin films using ion implantation to form source and drain regions. The germanium alloy content in the films were: 0, 15, and 25 at%. For each content of germanium, the annealing temperature and time necessary to activate the implant, without degrading device performance due to hydrogen effusion, was determined. The time necessary to anneal aluminum to form ohmic contacts at the optimal anneal temperature (260°C) was also determined. Thin-film transistors were characterized, and important device parameters such as: saturation mobility, threshold voltage, subthreshold swing, and ON-OFF current ratio were determined.