Electrical Instability of p-Channel SnO Thin-Film Transistors Under Light Illumination

We investigated the effects of illumination and bias illumination stresses on the electrical performance of p-type tin monoxide (SnO) thin-film transistors (TFTs). The transfer curve shifts in the positive direction with an increase of the subthreshold slope (SS) and OFF-current (I
_OFF
) under light illumination, where the increase in SS and I
_OFF
under illumination was attributed to the photoconductivity in SnO, especially at the back channel region. The positively shifted transfer curve by light illumination recovers to the initial one within 3000 s after turning OFF the light source. The trapping and detrapping of the photogenerated electrons in bulk defect states of SnO were considered as the most probable mechanism for the illumination-induced positive shift of the transfer curve and persistent photoconductivity in p-type SnO TFTs. There was no significant difference in the degree of light-induced-degradation between the TFTs with and without a passivation layer, which was mainly attributed to the weak chemisorption of oxygen molecules on SnO. Threshold voltage shift (ΔV
_th
) is much decreased under negative bias illumination stresses than under negative bias stresses, but ΔV
_th
increases under positive bias illumination stresses than under positive bias stresses in p-type SnO TFTs.