Stabilities of amorphous indium gallium zinc oxide thin films under light illumination with various wavelengths and intensities

摘要

We investigated the photo responses of an amorphous indium gallium zinc oxide (a-IGZO) thin film under light illumination with various wavelengths and intensities. By using the measured photo-conductivities of a-IGZO thin films, we extracted the photo excitation activation energy and dark relaxation activation energy through extended stretched exponential analysis. The stretched exponential analysis was found to describe well both the photoexcitation and the dark-relaxation characteristics. These analyses indicated that recombination takes place more slowly and through activation processes that are more deeply bound with the broader distribution of activation energies (E_(ac)) than those corresponding to the photo-generation process. The longer wavelength of the incident light, the slower the dark-relaxation occurs because of the formation of higher E_(ac) for the ionized oxygen vacancy (V_o~(2+)) states. For the dark-relaxation process, we also observed that the stretching exponent increases and the distribution of energy levels became narrower for longer wavelengths. This suggests that the neutralization of V_o~(2+) to V_o is slower for longer wavelengths due to the higher energy barrier height (E_(ac)) for the neutralization of V_o~(2+).