Using mathematical modeling in the Geant4 software package designed for simulating particle transport through matter via the Monte Carlo method and taking into account the self-absorption effect, the optimal thickness of the 63Ni beta source for a betavoltaic energy converter was determined. The surface activity reaches 90 % relative to the saturation value at a source thickness of 2 µm and is equal to 4.6‧108 Bq/cm2. The electron energy spectra on the source surface were calculated as a function of its thickness. These spectra were used for optimization of the parameters of a p-i-n barrier structure, in which beta-particles are absorbed, electron-hole pairs are generated and separated by a built-in electric field. According to the calculations, the maximum electric power generated by a GaN-based betavoltaic converter is equal to 0.12 μW‧cm–2, which corresponds to a betavoltaic conversion efficiency of 6.7 %. The results will be used in the design of a prototype of a gallium nitride betavoltaic energy converter.

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