Structural and electronic properties with respect to Si doping in oxygen rich ZnSnO amorphous oxide semiconductor

Abstract

The effect of Si doping in the presence of excess oxygen on the zinc-tin-oxide (ZTO) thin-film transistor is investigated. The threshold voltage increases from 3.86 to 10.8 V, and the ON current reduces from 4 x 10-4 to 1.1 x 10-4 A for the undoped and 1 wt % Si-doped ZTO transistor, respectively. The changes in the threshold voltage and the ON current are attributed to the suppression of free charge carriers due to excess oxygen in the film. The annihilation of oxygen vacancy-related defects states is substantiated by the density of states extracted from the photonic capacitance-voltage characteristic of the undoped and Si-doped ZTO thin-film transistors. Moreover, due to the high binding energy of Si and oxygen, excess oxygen is introduced into the film. The excessive oxygen forms the O-Oex dimer that acts as the electron trap and degrades the device's stability. From the bias stress measurement and the density of states extraction, it is concluded that 0.5 wt % doping of Si in ZTO is optimal for moderate device performance, less defects density, and high stability.