Through-Process Analytical Modeling of Photoconductance Spectrum for Porous ZnO Nanocrystalline Film

Abstract

In the past decades, many models have been developed to describe the photoconductance and the related photoresponse phenomena in wide-band gap metal oxides, but the related mechanisms and kinetics are still confused. Here, based on the persistent photoconductance observed in the porous ZnO nanocrystalline film, a donor photoionization model (DPM) is proposed to decipher the photoelectric kinetics both upon the sub-band gap and the above-band gap illuminations. In the DPM, the reaction rate equations and the related analytical functions are employed to numerically model the through processes of photoconductance spectra in a time-domain by comprehensively considering the photoelectric processes in ZnO such as the band-to-band transition, the donor photoionization, the surface oxygen adsorption/desorption, and the photogenerated electron recapture by donors. In the DPM simulation processes, some essential parameters, such as the electron yield from donor photoionization, the electron capture rates by donors, and the oxygen adsorption reaction rates on ZnO surface, are extracted quantitatively from the photoconductance spectra. The DPM analytical process herein reveals the photoresponse kinetics in detail and proposes a new insight into the basic theory of metal oxide photoresponse that might be helpful for further understanding the photoexcited carrier kinetics and the related photochemical processes.