Capacitance analyses of hydrogenated nanocrystalline silicon based thin film transistor

The capacitance–voltage (C–V) measurements within 106–10− 2 Hz frequency range were performed on the hydrogenated nanocrystalline silicon (nc-Si:H) bottom-gate thin film transistor (TFT) and metal-insulator-amorphous silicon (MIAS) structure, mechanically isolated from the same TFT. It was found that the conducting thin layer in nc-Si:H film expands the effective capacitor area beyond the electrode in the TFT structure, which complicates its C–V curves. Considering the TFT capacitance-frequency (C–F) curves, the equivalent circuit of the TFT structure was proposed and mechanism for this area expansion was discussed. On the other hand, the MIAS C–F curves were fitted by the equivalent circuit models to deduce its electrical properties. nc-Si:H neutral bulk effect was revealed by the dependence of the MIAS capacitance on frequency within 106–103 Hz at both accumulation and depletion regimes. The inversion in MIAS was detected at 102–10− 2 Hz for relatively low negative gate bias without any external activation source. The presence of the ac hopping conductivity in the nc-Si:H film was inferred from the fitting. In addition, the density of the interface traps and its energy distribution were determined.