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The conversion of energy of electrons produced by a radioactive β-source into electricity in a Si and SiC n p  junctions is modeled. The features of the generation function that describes the electron-hole pair production by an electron flux and the emergence of a "dead layer" are discussed. The collection efficiency Q that describes the rate of electron-hole pair production by incident beta particles, is calculated taking into account the presence of the dead layer. It is shown that in the case of high-grade Si n p  junctions, the collection efficiency of electron-hole pairs created by a high-energy electrons flux (such as, e.g., Pm-147 beta flux) is close or equal to unity in a wide range of electron energies. For SiC p -n junctions, Q is near unity only for electrons with relatively low energies of about 5 keV (produced, e.g., by a tritium source) and decreases rapidly with further increase of electron energy. The conditions, under which the influence of the dead layer on the collection efficiency is negligible, are determined. The open-circuit voltage is calculated for realistic values of the minority carriers' diffusion coefficients and lifetimes in Si and SiC n p  junctions, irradiated by a high-energy electrons flux. Our calculations allow to estimate the attainable efficiency of betavoltaic elements.

Conversion of energy of beta-particles into electric energy in a p-n junction based on directbandgap semiconductors, such as GaAs, considering realistic semiconductor system parameters is analyzed. An expression for the collection coefficient, Q, of the electron-hole pairs generated by beta-electrons is derived taking into account the existence of the dead layer. We show that the collection coefficient of beta-electrons emitted by a 3 H-source to a GaAs p-n junction is close to 1 in a broad range of electron lifetimes in the junction, ranging from 10 −9 to 10 −7 s. For the combination 147 Pm/GaAs, Q is relatively large (≥ 0.4) only for quite long lifetimes (about 10 −7 s) and large thicknesses (about 100 µm) of GaAs p-n junctions. For realistic lifetimes of minority carriers and their diffusion coefficients, the open-circuit voltage realized due to the irradiation of a GaAs p-n junction by beta-particles is obtained. The attainable beta-conversion efficiency η in the case of a 3 H/GaAs combination is found to exceed that of the 147 Pm/GaAs combination.

Dark I-V curves of silicon solar cells with various Shockley-Reed-Hall lifetimes have been studied. The lifetimes are determined from the short-circuit-current internal quantum yield. The recombination currents in the space charge region (SCR) are found to be formed within time intervals that are at least an order of magnitude shorter than the charge-carrier bulk lifetime. This effect can be associated with a high defect concentration (and, therefore, a high deep-level concentration) in the SCR of examined Si structures. The parameters of deep centers that are responsible for the recombination in the SCR have been evaluated.

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