The research team led by Professor Park Kwang-wook of Jeonbuk National University (JBNU), Division of Advanced Materials Engineering (Electronic Materials Engineering), together with the research team of Professor Lee Han-eol of the Department of Materials Science and Engineering at the Gwangju Institute of Science and Technology (GIST), who is concurrently affiliated with the Next-Generation Energy Research Institute RISE, implemented a self-powered photodetector by precisely controlling the composition and electrical properties of zinc tin nitride (ZnSnN2). PhD candidates Kim Jeong-hyun and Hwang Ju-chan of JBNU served as co-first authors of the study.

Photodetectors, which convert light into electrical signals, are used in a variety of fields such as the Internet of Things (IoT), wearable devices, and drones. In particular, self-powered photodetectors that use light itself as an energy source can reduce external power consumption and are drawing attention as a key technology for next-generation low-power electronic devices.

For a self-powered photodetector to operate, photo-generated electrons and holes must be effectively separated. To achieve this, a heterojunction structure that forms an internal electric field at the junction by combining different semiconductors is used. In such structures, precise control of each semiconductor's carrier concentration and energy band structure is essential.

The JBNU research team focused on ZnSnN2, a next-generation nitride semiconductor. ZnSnN2 is a ternary nitride semiconductor composed of abundant elements zinc (Zn), tin (Sn), and nitrogen (N). It has high structural affinity with conventional III-nitrides such as GaN and its electrical and optical properties can be widely tuned by composition and growth conditions, making it an attractive material for next-generation optoelectronic devices.

The research team precisely controlled the composition and carrier concentration of ZnSnN2 thin films by adjusting the nitrogen-to-argon ratio in a reactive RF magnetron sputtering process. In the optimized ZnSnN2 films, they achieved a carrier concentration of 3.34 × 10^19 cm^-3 and formed a strong internal electric field of approximately 88 kV/cm in the ZnSnN2/GaN heterojunction. This internal electric field plays a key role in effectively separating photo-generated charges and producing photocurrent without an external voltage.

The collaborative team also patterned periodic microhole structures on the ZnSnN2 surface to trap and enhance light absorption. As a result, the lifetime of photoexcited charge carriers increased from about 3.5 nanoseconds (ns) in the planar structure to up to 6.2 ns, an approximate 1.8-fold improvement.

The developed ZnSnN2/GaN photodiodes exhibited stable photoresponse at 0 V without external bias and operated under low light intensity. The researchers demonstrated in a practical system that combining the photodiode with a commercial temperature-humidity sensor can reduce the external power required to drive the sensor by using power generated from ambient light.

This study is significant in that it controlled the composition and electrical properties of the next-generation semiconductor ZnSnN2 from the thin-film growth stage and linked this control to the design of an internal electric field in a GaN heterojunction and light-absorption structures.

Professor Park Kwang-wook stated, "ZnSnN2 is composed of abundant elements and its electrical and optical properties can be widely tuned by growth conditions and composition, so it has great potential as a next-generation semiconductor material. This study is meaningful because we precisely controlled the properties of ZnSnN2 to form a strong internal electric field in a heterojunction with GaN and applied it to a real self-powered photonic device."

This research was supported by the Ministry of SMEs and Startups' Technology Development Project (RS-2025-25465868), a National Research Foundation of Korea research project funded by the Ministry of Science and ICT (NRF-2022R1F1A1064130), JBNU's BK21 FOUR program, and JBNU research funding.

The research results were published in the international journal 'Small Structures' under the title "Self-Powered ZnSnN2/GaN Photodiodes via Fine Stoichiometry Control and Photon Trapping Micropatterned Heterojunctions Under Low-Light Irradiation" (DOI: 10.1002/sstr.70572).