Roles of core-shell and δ-ray kinetics in layered BN α-voltaic efficiency

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α-voltaics harvest electron-hole pairs created as energetic α particles collide with and ionize electrons in a semiconductor, creating δ-rays. After ionization, charged pair production continues through δ-ray impact ionization events and the Auger relaxation of core-shell holes created through K-shell ionization events. Secondary ionization events are quantified using the TPP-2M model, the fraction of K-shell ionization events is determined using the energy-loss Coulomb-repulsion perturbed-stationary-state relativistic theory, and the relaxation of the resulting holes is treated with a fully ab initio approach using multiple Fermi golden rule calculations for ranges of carrier concentrations and temperatures. The limiting rate is 15 ns−1 for small carrier concentrations and high temperatures, as compared to the radiative core-shell relaxation rate estimated here at 20 ns−1, indicating that Auger modes contribute significantly. Moreover, the K-shell ionization events are shown to dominate for low energy α particles and vanish for high energy ones. Thus, the efficiency loss due to energy dissipation in the fuel layer is mitigated, which is demonstrated by the analysis of a layered fuel-voltaic device with an efficiency from 20% to 14% for fuel layers between 5 and 10 μm thick. The design of a α-voltaic integrated with a thermoelectric generator is suggested for improved efficiency and the system-level mitigation of radiation damage and geometric inefficiency.