Breaking the myth: Wide-bandgap semiconductors not always the best for betavoltaic batteries

Betavoltaic batteries are appealing power sources for micro-power systems and applications in extreme environments due to their superlong lifetimes, high energy densities, and impressive environmental adaptability. However, little work has been done on building a comprehensive device model with the consideration of all the physical processes. In this work, we proposed one device model integrating models of both radioactive sources and semiconductor units, aiming to guide the design of high-performance devices under specific application requirements. A systematical investigation was conducted on the determining factors on energy losses in planar betavoltaic batteries consisting of typical β sources, such as ¹⁴⁷Pm₂O₃, Ti³H₂, ⁶³Ni, and ¹⁴C(PMMA), and semiconductors, including Si, GaAs, GaP, SiC, and GaN. Our results show that the output power and the emitting β particle energy of radioactive sources will cause the difference in the major energy loss mechanisms, leading to the different selection rules for semiconductor units. The well-accepted conclusion that efficiency of betavoltaic batteries increases with the width of bandgap no longer holds any more, especially considering high-output power sources and the reality of semiconductor technology. The device model developed in this work provides a powerful tool for the design of high-performance betavoltaic batteries applied in various occasions and will effectively guide the fabrication of high-performance devices.