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

Abstract

SnO 2 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, SnO 2 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 SnO 2 thin films. The SnO 2 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 SnO 2 lattice as the Zn content was less than 10 mM. As the Zn content exceeded 30 mM, a secondary phase, Zn 2 SnO 4 , was formed in the SnO 2 layer. The undoped SnO 2 exhibited n-type conductivity with a charge carrier concentration of 5.77 × 10 19 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 × 10 13 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 SnO 2 thin film without any interference from daylight.

The enhanced responsivity and response speed of SnO2 visible-blind transparent photodetectors via the SiO2 passivation layer

“…5(a), the band gap energy of SnO 2 was calculated to be 3.75 eV from the Tauc curve, which is similar to the previously reported results. 28,29 In addition, the transmittances of both SnO 2 and SnO 2 /SiO 2 hybrid films were more than 75% throughout the visible band from 400 nm to 700 nm as shown in Fig. 5(b), which can meet the requirement of applications with high transparency.…”

Persistent Photoconductivity of Metal Oxide Semiconductors

“…Due to the rightward shift in the configuration coordinates of heavily doped samples, the capture potential barrier increases, resulting in a more stable PPC. In addition to Pb 2+ , the doping of zinc (Zn) also has a significant impact on the SnO 2 ’s PPC . As the Zn doping concentration in SnO 2 films increases to 10 mM, the carrier concentration sharply decreases, reducing the dark current.…”

“…(d) Mechanism of photoresponse in undoped and Zn-doped SnO 2 thin films before and after UV exposure. Reproduced from ref . Copyright 2023 American Chemical Society.…”

“…As discussed earlier, the PPC phenomenon was observed across various metal oxide systems. It is worth noting that, in many publications, applications of the PPC effect have not been proposed, and in some cases, the PPC effect has been investigated as a characteristic to be eliminated. , Nevertheless, in recent years, the perspective of PPC as an exploitable trait has gained attention. The PPC effect has found applications in a multitude of areas such as optoelectronic synapses, optical memories, charge storage, solar cells, artificial vision, selective photodoping, and more within the realms of optoelectronics and micro/nanoelectronics.…”