Experimental and simulation study of ZnO nanowire/Si heterojunctions as radioisotope batteries for long-term micro-power applications

Betavoltaic batteries are emerging as a critical power solution for microelectronic systems requiring decades of maintenance-free operation. Among wide-bandgap semiconductors, zinc oxide (ZnO) is particularly attractive due to its radiation resistance and compatibility with silicon technology. In this work, we report the first experimental fabrication and characterization of ZnO/Si heterojunction betavoltaic cells using a 63 Ni beta source. Unlike previous studies limited to ZnO/n-Si junctions, we systematically investigated both ZnO/p-Si and ZnO/n-Si configurations, demonstrating that the ZnO/p-Si heterojunction exhibits superior performance owing to its intrinsic p–n junction, which enhances charge carrier separation under beta irradiation. ZnO nanowires (∼1 µm) were synthesized via a sol–gel method and deposited on silicon substrates by spin-coating to form heterojunctions. Structural (XRD, TEM, FESEM) and electrical characterizations confirmed device formation, with the p-Si/ZnO junction achieving a short-circuit current of 6 nA and an open-circuit voltage of 2.5 mV, compared to 0.04 nA and 6 mV for the n-Si/ZnO junction. To explain the discrepancy between simulated and measured efficiencies, we developed a comprehensive MCNP–TCAD simulation framework, which revealed that contact resistance, interface traps, and air–gap effects are dominant loss mechanisms. The model showed excellent agreement with experimental data and provided design strategies for performance enhancement. This study establishes a validated simulation–experiment correlation, identifies key efficiency-limiting factors, and introduces a scalable fabrication route for ZnO/Si betavoltaic devices. The insights gained here offer valuable guidance for advancing high-efficiency, radiation-resistant nuclear micro-batteries for future IoT, space, and biomedical applications.