Characterization of Interface State Density from Subthreshold Slope of MOSFETs at Low Temperatures (≥ 10 K)
We have evaluated interface state density (DIT) for EC−ET > 0.00 eV from the subthreshold slope deterioration of MOSFETs at low temperatures. We have compared two n-channel MOSFETs on the C- and a-faces with the gate oxide formed by pyrogenic oxidation followed by annealing in H2. The peak field-effect mobility (µFE,peak) for the C-face MOSFET was 57 cm2V-1s-1 at 300 K, which is lower than the half of 135 cm2V-1s-1 for the a-face MOSFET. We have shown that DIT very close to EC can well explain why µFE for C-face MOSFETs is lower than that for a-face MOSFETs. The value of DIT at 0.00 eV corresponding to the subthreshold slope at 11 K was 1.6×1014 cm-2eV-1 for the C-face MOSFET, which is more than the double of 6.4×1013 cm-2eV-1 for the a-face MOSFET.