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.