Evaluation of Minority Carrier Generation Lifetime for Oxide Semiconductors

In this study, the transfer characteristics of InGaZnO (IGZO) and InSnZnO (ISZO) thin-film transistors are compared using the minority carrier generation lifetime method. Capacitance-voltage and capacitance-time characteristics of IGZO- and ISZO-based capacitors with a p⁺-Si/SiO₂/IGZO or ISZO structure were evaluated at a 100 kHz frequency. Although the intrinsic carrier concentrations of IGZO and ISZO films are on the order of ~10⁻⁷ cm⁻³, which is conjectured to result in a very low off-state drain current (I_D,OFF), even as small as zero, a magnitude of 10⁻¹² – 10⁻¹¹ A for I_D,OFF was measured in this study. We propose that this is due to the minority carriers, which are thermally generated from the channel defects. Furthermore, ISZO films exhibited faster transient capacitance characteristics compared to the IGZO films, which is associated with the amount of defect sites in the channel substrate. Thus, the lower transient time for the ISZO films is attributed to a larger number of oxygen vacancies in the channel layer than in IGZO films.