The Influence of Bulk and Interface Gap States on the Performance of Amorphous Silicon Thin Film Transistors

Abstract

AbstractAmorphous silicon thin film transistors with on/off ratios >108 and on currents >100 μA for supply voltages <30 V have been manufactured. The transistors are of the structure glass/Cr/SiNx/intrinsic a-Si/n+a-Si/Al. The field effect electron mobility is typically 0.24 cm2 /Vs. Evaluation of quasistatic CV measurements yields a gap state density of 3.2*1016 cm−3eV−1 at midgap. A one-dimensional model calculation describing the influence of bulk and interface gap states and various other material and geometry parameters on transistor performance is outlined. Calculated data include space charge density, spatial distribution of band bending, band bending vs gate source voltage, static capacitance, and channel conductance. A fit calculation for the experimental sub pinch-off transfer characteristic of a thin film transistor is presented.