Comparative study of C–V-based extraction methods of interface state density for a low-temperature polysilicon thin film

To extract comprehensive and accurate interface state density ( D it ) distribution for a low-temperature polysilicon (LTPS) thin film, three well-established methods based on capacitance–voltage ( C – V ) measurements were compared: high–low frequency capacitance, conductance, and quasi-static (QS) capacitance methods. Because of the strong frequency-dependent response of grain boundary traps within the LTPS, C – V measurements are necessary on p- as well as n-type LTPS films, as they provide D it distribution across the entire LTPS band gap. The QS capacitance method, which uses an optimal high-frequency C – V curve with a minimal grain boundary trap response, provided the best and most comprehensive estimate of D it distribution across the LTPS band gap, even at room temperature (25 °C). Although the narrow extraction ranges of D it were extended toward the mid-gap region by increasing the measurement temperature in both high–low frequency capacitance and conductance methods, the responses of the grain boundary traps still overestimated the D it values near the band edges.