Effects of initial annealing treatments on the electrical characteristics and stability of unpassivated CdSe thin film transistors

Abstract

Secondary ion mass spectrometry shows that when CdSe is annealed in air at 350 °C oxygen diffuses inside the grains and the diffusion is enhanced at the grain boundaries. Subsequent vacuum annealing removes oxygen from inside the grains and from the grain boundaries, but leaves a film with residual tightly bound oxygen and a reduced donor concentration. Annealing in vacuum at 390 °C results in a highly conductive layer with a positive threshold voltage drift resulting from the chemisorption of oxygen. Annealing in dry or wet air at 350 °C produces a highly resistive material with lower donor concentrations at the surface and in the bulk, and a lower concentration of acceptor traps at the grain boundaries. The effects of dry- and wet-air annealing on the threshold voltage drift for unpassivated CdSe thin film transistors exposed to ambient air have been monitored. A negative threshold voltage drift, which may be enhanced by the presence of a water-related species, was observed.