EFFECTS OF INITIAL ANNEALING TREATMENTS ON THE ELECTRICAL CHARACTERISTICS AND STABILITY OF UNPASSIVATED CDSE THIN-FILM TRANSISTORS

Secondary ion mass spectrometry shows that when CdSe is annealed in ai r at 350 degrees C oxygen diffuses inside the grains and the diffusion is enhanced at the grain boundaries, Subsequent vacuum annealing remo ves oxygen from inside the grains and from the grain boundaries, but l eaves a film with residual tightly bound oxygen and a reduced donor co ncentration. Annealing in vacuum at 390 degrees C results in a highly conductive layer with a positive threshold voltage drift resulting fro m the chemisorption of oxygen. Annealing in dry or wet air at 350 degr ees C produces a highly resistive material with lower donor concentrat ions at the surface and in the bulk, and a lower concentration of acce ptor traps at the grain boundaries. The effects of dry-and wet-air ann ealing on the threshold voltage drift for unpassivated CdSe thin film transistors exposed to ambient air have been monitored, A negative thr eshold voltage drift, which may be enhanced by the presence of a water -related species, was observed. (C) 1998 American Vacuum Society. [S07 33-2101(98)04402-9].