Steady-state photoconductivity of amorphous In–Ga–Zn–O

Photoresponse was investigated for an amorphous oxide semiconductor, In–Ga–Zn–O, by the steady-state photoconductivity (SSPC) method. All the films exhibited extremely slow reversible photoresponses. Analysis of the transient photocurrent at varied temperatures provided similar activation energies of ~ 0.5 eV for both the time constants and the photoconductivity. Mobility–lifetime (μτ) products were estimated from the photoconductivity spectra measured at the sweep rate of 2 nm/s, which monotonically increased with increasing dark conductivity σD (i.e. the Fermi level EF becomes shallower). The obtained μτ values are larger than those of hydrogenated amorphous silicon even if the EF dependence is considered.