Reversible Control of In-Gap States from Surface Oxygen Vacancies in Perovskite Stannates with Ultraviolet Light

Controllable optoelectronic devices require the reversible manipulation of photo-carrier recombination process by in-gap defect states in state-of-the-art oxide semiconductors. Nevertheless, previous researches to generate oxygen vacancies as an origin of in-gap states of oxide semiconductors have struggled with the reversible and spatially confined control of oxygen vacancies and their related phenomena.<br/>In this presentation, a novel method to reversibly control the surface-limited-photoconductivity from oxide semiconductors is demonstrated by photochemical reaction under the illumination of ultraviolet light at room temperature. Significantly, the trap-free photocurrent of illuminated BaSnO₃in air (~ 200 pA) was reversibly changed into higher photocurrent of illuminated BaSnO₃ under vacuum (~ 335 nA) with persistent photoconductivity in accordance with ambient oxygen atmosphere under illumination. By various characterizations along with theoretical calculation, unlike other oxide semiconductors, ultraviolet illumination of BaSnO₃ under low oxygen partial pressure generate oxygen vacancies at surface, which cause in-gap defect states at 2.53 eV from the band edge in consequence of surface photolysis together with low oxygen diffusion coefficient of BaSnO₃; the concentrated oxygen vacancies are supposed to lead to two-step transition of photocurrent response by modifying the characteristics of in-gap defect states. These results suggest a new method to control the functionalities associated with surface defect states by light-matter interaction in a reversible and spatially confined way for the innovative application using emerging oxide semiconductors.