Electrode interdependence and hole capacitance in capacitance–voltage characteristics of hydrogenated amorphous silicon thin-film transistor

The interelectrode capacitance–voltage (C–V) characteristics of back-channel-etched inverted-staggered hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were investigated. It is demonstrated that this simple measurement can be used to diagnose TFT parameters such as the fabricated channel length, the channel resistance, and the error in the mask alignment of the source and drain overlap lengths. The C–V characteristics associated with the hole accumulation in a-Si:H TFTs with n+-type source/drain contacts were also examined. We observed that the ac capacitance increases for low frequencies and/or moderately high measurement temperatures provided the gate voltage is sufficiently negative. One possible mechanism for this hole capacitance is proposed that accounts for the observed frequency and temperature dependence.