This is a novel SiC betavoltaic device (as an example) which comprises one or more “ultra shallow” P+N− SiC junctions and a pillared or planar device surface (as an example). Junctions are deemed “ultra shallow”, since the thin junction layer (which is proximal to the device's radioactive source) is only 300 nm to 5 nm thick (as an example). In one example, tritium is used as a fuel source. In other embodiments, radioisotopes (such as Nickel-63, promethium or phosphorus-33) may be used. Low energy beta sources, such as tritium, emit low energy beta-electrons that penetrate very shallow distances (as shallow as 5 nm) in semiconductors, including SiC, and can result in electron-hole pair creation near the surface of a semiconductor device rather than pair creation in a device's depletion region. By contrast, as a high energy electron penetrates a semiconductor device surface, such as a diode surface, it produces electron hole-pairs that can be collected at (by drift) and near (by diffusion) the depletion region of the device. This is a betavoltaic device, made of ultra-shallow junctions, which allows such penetration of emitted lower energy electrons, thus, reducing or eliminating losses through electron-hole pair recombination at the surface.