Effects of laser radiation on glow-discharge amorphous-silicon diodes

Both ruby laser and CW argon ion laser irradiation increase the electrical conductance of doped hydrogenated amorphous-silicon films. The ruby laser produces the larger effect, not only due to activation of phosphorus dopant in the film, but also as the films are crystallised. These permanent conductivity changes are distinct from the reversible changes observed in lightly doped or undoped films. These latter changes have dramatic effects on the current/voltage behaviour of Ni or Al Schottky diodes owing to changes in the density of gap states, and may be reversed by thermal annealing to 150°C. Because of the increased dielectric relaxation time of laser-irradiated films, the capacitance/frequency curves no longer give a clear indication of space-charge width. Al diodes have an additional irreversible change produced by laser diffusion of Al or oxygen, and are greatly improved rectifying devices after laser irradiation and thermal annealing.