Persistent Photoconductivity Control in Zn-Doped SnO2 Thin Films for the Performance Enhancement of Solar-Blind Ultraviolet Photodetectors

SnO2 has received much attention as one of the transparent oxide semiconductors, which can be used in various applications, such as photocatalysts, chemical sensors, and ultraviolet (UV) photodetectors. However, SnO2 has suffered from severe persistent photoconductivity, which degraded the photodetector performance by slowing the response speed. Here, we report the effective control of persistent photoconductivity and enhanced the performance of the UV photodetector based on Zn-doped SnO2 thin films. The SnO2 thin films with the Zn content varying from 0 to 50 mM were grown by spray pyrolysis deposition. The structural and chemical investigations verified that the Zn atoms were successfully incorporated into the SnO2 lattice as the Zn content was less than 10 mM. As the Zn content exceeded 30 mM, a secondary phase, Zn2SnO4, was formed in the SnO2 layer. The undoped SnO2 exhibited n-type conductivity with a charge carrier concentration of 5.77 × 1019 cm–3, which resulted in a high dark current with severe persistent photocurrent. As the doping content increases to 10 mM, the charge carrier concentration drastically reduces to 3.65 × 1013 cm–3, significantly reducing dark current and persistent photoconductivity. Therefore, Zn doping played a critical role in enhancing the solar-blind UV photodetector performances by increasing the photosensitivity and shortening the response times. The free-space optical communication system was successfully demonstrated by using the solar-blind UV photodetector based on the Zn-doped SnO2 thin film without any interference from daylight.