【Member Papers】Design of high-efficiency Ga₂O₃-based betavoltaic battery utilizing the MG-HJ-PND structure

      Researchers from the Xidian University and Xi'an Jiaotong University and Northwest Institute of Nuclear Technology have published a dissertation titled "Design of high-efficiency Ga₂O₃-based betavoltaic battery utilizing the MG-HJ-PND structure" in Applied Physics Letters.

Project Support

      This work was supported in part by the National Natural Science Foundation of China under Grant No. 62204198, in part by Steady Support Fund for National Key Laboratory under Grant No. JBSY252800260, the State Key Laboratory of Wide-Bandgap Semiconductor Devices and Integrated Technology under Grant No. 2413S121, and the Fundamental Research Funds for the Central Universities under Grant No. xxj032025008.

Background

      Voltaic batteries are widely applied in micro-electromechanical systems and implantable medical fields, representing vital choices for long-service, maintenance-free energy systems. Typically, the voltaic battery consists of a radioactive source and a semiconductor conversion device, and the fundamental principle of the voltaic nuclear battery is to convert energy from the decay energy of a radioactive source into electrical energy. Figure 1 shows that radioactive sources continuously generate radiation-generated electron–hole pairs (RG-EHPs) through ionization in the half-life period. The RG-EHPs in the depletion region are separated under the influence of the built-in electric field, giving rise to radiation-generated current density (J_RG), which is converted into the electrical energy of the betavoltaic battery. In voltaic battery applications, miniaturization and ease of shielding are essential requirements. Short-range, low-energy, and long half-life beta (β) radioactive sources such as Ti³H₂, ⁶³Ni, and ¹⁴⁷Pm₂O₃ are the optimal choices for miniaturization and shielding. Although the energy deposition depth of the β radioactive sources in the semiconductor conversion device is only a few micrometers, β radioactive sources still cause significant radioactive damage to the semiconductor conversion device. Gallium oxide (Ga₂O₃), an ultra-wide bandgap semiconductor, offers strong radiation resistance and has advanced rapidly in recent years. With broad applications in power electronics and radiation detectors, Ga₂O₃ is also a promising material for semiconductor conversion devices.

Abstract

      Attributed to the wide bandgap property of gallium oxide (Ga₂O₃), Ga₂O₃-based betavoltaic batteries offer advantages such as small volume, strong radiation resistance, high-temperature stability, and chemical stability, demonstrating great potential for micro-medical devices, aerospace systems, and military equipment. Typically, betavoltaic batteries are based on a diode structure. However, the high carrier concentration in Ga₂O₃ material results in an excessively thin depletion region at zero bias. This limitation reduces the efficiency of collecting radiation-generated electron–hole pairs (RG-EHPs) in Ga₂O₃-based betavoltaic batteries, resulting in a low energy conversion efficiency (η_c), a crucial indicator for evaluating the performance of betavoltaic batteries. In this study, Ga₂O₃-based betavoltaic batteries utilizing diode structures were investigated using Monte Carlo FLUKA particle transport software and Sentaurus TCAD semiconductor device simulation software. A Ga₂O₃-based betavoltaic battery featuring a multi-groove heterojunction PN diode structure (MG-HJ-PND) was designed, with the radioactive source positioned within the grooves and p-nickel oxide (p-NiO) injected along the groove edges, which not only enhanced RG-EHP generation but also extended the depletion region, ultimately achieving a high η_c of 10.38% in the Ga₂O₃-based betavoltaic battery. Moreover, the performance of the Schottky barrier diode and heterojunction PN diode (HJ-PND) structures based on Ga₂O₃, silicon, and silicon carbide material was compared. The high-efficiency Ga₂O₃-based betavoltaic battery, based on the MG-HJ-PND structure, was shown to be a promising candidate for permanent micro-energy sources.

Conclusion

      In summary, simulation models of Ga₂O₃-based betavoltaic batteries utilizing SBD and HJ-PND structures were established using the Monte Carlo FLUKA particle transport software and Sentaurus TCAD semiconductor device simulation software. By analyzing the J–V output characteristic curve, two effective ways to enhance η_c were identified: increasing the number of RG-EHPs and improving the collection efficiency from RG-EHPs to J_RG. The increase in RG-EHPs was sequentially achieved by removing the metal electrodes, introducing the groove structure, and thinning the p-NiO layer. Moreover, by adding p-NiO and increasing the p-NiO length, the depletion region was enlarged, achieving the goal of improving the collection efficiency of RG-EHPs. These optimizations increased J_sc, V_oc, and FF in the J–V output characteristic curve. Ultimately, this work improved the performance indicator of η_c by designing Ga₂O₃-based betavoltaic battery structures. High η_c values of 5.0% (Ti³H₂), 10.4% (⁶³Ni), and 2.3% (¹⁴⁷Pm₂O₃) were achieved in Ga₂O₃-based MG-HJ-PND betavoltaic batteries. These high-efficiency Ga₂O₃-based betavoltaic batteries show strong potential for micro-electromechanical systems and implantable medical devices as maintenance-free energy sources.