Self-Powered ZnSnN₂/GaN Photodiodes via Fine Stoichiometry Control and Photon Trapping Micropatterned Heterojunctions Under Low-Light Irradiation

Recent advances in energy-autonomous optoelectronic devices have attracted significant attention for next-generation applications. However, developing compound semiconductor-based self-powered photodiodes remains challenging due to difficulties in precise band alignment control and limited light absorption efficiency. Here, we demonstrate a self-powered photodiode based on a ZnSnN₂ (ZTN)/GaN heterostructure, featuring an enhanced built-in electric field via fine stoichiometry control and light-trapping micropatterned heterojunctions. Through stoichiometric engineering, the ZTN thin-film exhibited an optimized carrier concentration of 3.34 × 10¹⁹ cm⁻³ and a bandgap of 2.27 eV. Consequently, the heterostructure achieved a strong built-in electric field of 88 kV cm⁻¹ due to the degenerate n-type properties of ZTN. To further reinforce light absorption, we introduced periodic microhole patterns, and the resulting micropatterned heterojunction exhibited a substantial carrier lifetime of 6.2 ns, representing a 1.8-fold enhancement over the thin-film structure. Finally, the device demonstrated robust power-saving operation under zero-bias conditions, successfully driving a commercial temperature/humidity sensor. Moreover, the device exhibited a linear dynamic range of 15.1 dB and stable linearity (θ ≈ 0.27) even under low-light conditions, ensuring reliable operation in varying illumination environments. These results suggest that our dual approach of stoichiometric and structural engineering offers a scalable pathway for next-generation self-powered optoelectronic systems.