THERMAL BIAS ANNEALING EVIDENCE FOR THE DEFECT POOL IN AMORPHOUS-SILICON THIN-FILM TRANSISTORS

Thin-film transistors were thermally annealed while a bias voltage was applied to the gate electrode. The transfer characteristics were then measured, and the density of states distributions derived by field-effect analysis. The results indicate that the equilibrium distribution and number of defects in the transistor channel region depend on the position of the Fermi energy during annealing. Thus the density of states can be increased or decreased in parts of the band gap. A high Fermi energy during annealing results in few states high in the gap and more states low in the gap. The reverse is true for annealing while the Fermi energy is low. This is consistent with the defect pool model for silicon dangling bond states and suggests that most deep states are part of the defect pool.