Abstract: Isotope source energy deposition along the thickness direction of a semiconductor is calculated, based upon which an ideal short current is evaluated for betavoltaic batteries. Electron-hole pair recombination and drifting length in a PN junction built-in electric field are extracted by comparing the measured short currents with the ideal short currents. A built-in electric field thickness design principle is proposed for betavoltaic batteries: after measuring the energy deposition depth and the carrier drift length, the shorter one should then be chosen as the built-in electric field thickness. If the energy deposition depth is much larger than the carrier drift length, a multijunction is preferred in betavoltaic batteries and the number of the junctions should be the value of the deposition depth divided by the drift length.

Key words: betavoltaic battery, built-in electric field, electron-hole pair recombination, energy deposition