Drain-current distortion in CdSe thin-film transistors

CdSe thin-film transistors (TFT\´s) fabricated with the lift-off process were susceptible to reversible degradation during operation. In particular, when the drain voltage exceeded ∼ 10 V, the characteristics distorted. Current at low drain voltages was depressed, but current at high drain voltages was not. While the TFT was in the distorted state, it was possible by means of pulsed drive on the gate to observe negative differential conductivity. This distortion phenomenon was studied, and its source speculated upon. Factors believed to play a role are formation of deep traps, trapping of hot electrons in the gate insulator, depletion of carriers near the drain electrode, and tunneling of carriers through the depleted region at high drain voltages. Recovery occurs when the trapped electrons in the insulator are released. It is believed that residues of the lift-off process play a role in formation of these traps.