Light-Induced Peroxide Formation in ZnO: Origin of Persistent Photoconductivity

Abstract

The persistent photoconductivity (PPC) in ZnO has been a critical problem in opto-electrical devices employing ZnO such as ultraviolet sensors and thin film transistors for the transparent display. While the metastable state of oxygen vacancy (VO) is widely accepted as the microscopic origin of PPC, recent experiments on the influence of temperature and oxygen environments are at variance with the VO model. In this study, using the density-functional theory calculations, we propose a novel mechanism of PPC that involves the hydrogen-zinc vacancy defect complex (2H-VZn). We show that a substantial amount of 2H-VZn can exist during the growth process due to its low formation energy. The light absorption of 2H-VZn leads to the metastable state that is characterized by the formation of (peroxide) around the defect, leaving the free carriers in the conduction band. Furthermore, we estimate the lifetime of photo-electrons to be ~20 secs, which is similar to the experimental observation. Our model also explains the experimental results showing that PPC is enhanced (suppressed) in oxygen-rich (low-temperature) conditions. By revealing a convincing origin of PPC in ZnO, we expect that the present work will pave the way for optimizing optoelectronic properties of ZnO.

The Nature of the Oxygen Vacancy in Amorphous Oxide Semiconductors: Shallow Versus Deep

“…Although metastable, deep V O could also be present in films, but should be low in concentration. Accordingly, V O may not be a main source causing the device instability under NBIS, and other alternative mechanisms related to hydrogen impurities or peroxide formation are therefore worth close attention.…”

Tail state mediated conduction in zinc tin oxide thinfilm phototransistors under below bandgap optical excitation

“…It is widely considered that the oxygen vacancy defects are the major intrinsic origin of PPC effect in the oxide system. However, the effect of zinc interstitials or peroxide defects on the PPC is also proposed 56 , 57 . In the present case, in addition to the effect of oxygen vacancy on the PPC effect possibility of contribution from above mentioned two defects are verified.…”

Lanthanum Doping Enabling High Drain Current Modulation in a p-Type Tin Monoxide Thin-Film Transistor

“…In addition, we determined the chemical potential of La from La 2 Sn 2 O 7 . Since the hydrogen-related defects could be a source of carrier, , we calculated the defect formation energies of intrinsic defect, La substitutional defect, and hydrogen-related defects.…”