Roles of Core-Shell and ∂ -Ray Kinetics in Layered BN ∝ -Voltaic Efficiency

Abstract

alpha-voltaics harvest electron-hole pairs created as energetic a particles collide with and ionize electrons in a semiconductor, creating delta-rays. After ionization, charged pair production continues through delta-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 a 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 mu m thick. The design of a alpha-voltaic integrated with a thermoelectric generator is suggested for improved efficiency and the system-level mitigation of radiation damage and geometric inefficiency. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790506]