Amorphous silicon buried-channel thin-film transistors

We demonstrate a buried-channel thin-film field effect transistor (TFT) based on deposited silicon nitride and hydrogenated amorphous silicon with the conducting channel recessed approximately 50 Å from the interface. We fabricate transistors and capacitors by DC reactive magnetron sputtering of a silicon target in a plasma of (Ar+H ₂+N₂) or (Ar+H₂) for the nitride and silicon layers, respectively. To create a step in the conduction band, and thus a buried-channel, we vary the hydrogen partial pressure which varies the hydrogen content and the bandgap of amorphous silicon. Capacitance-voltage and current-voltage measurements on these devices present strong evidence for the existence of the buried-channel. We achieve a record field effect mobility in saturation of 1.68 cm² /V-s with amorphous silicon deposited at 230°C, and an acceptable mobility of 0.44 cm²/V-s with amorphous silicon deposited at 125°C