Efficiency analysis of betavoltaic elements

TL;DR

This paper models and analyzes the efficiency of betavoltaic elements using Si and SiC p-n junctions, focusing on electron-hole pair collection efficiency and the impact of a dead layer, providing insights into their energy conversion performance.

Contribution

It introduces a detailed model of electron-hole pair generation and collection efficiency in Si and SiC betavoltaic devices, accounting for the dead layer and high-energy electron flux effects.

Findings

High-grade Si p-n junctions achieve near-unity collection efficiency for high-energy beta particles.

SiC junctions have high efficiency only at low electron energies (~5 keV).

Conditions are identified where the dead layer's impact on efficiency is negligible.

Abstract

The conversion of energy of electrons produced by a radioactive source into electricity in a Si and SiC $\textit{p-n}$ junctions is modeled. The features of the generation function describing the electron-hole pair production by an electron flow and the emergence of a "dead layer" are discussed. The collection efficiency, $Q$, describing 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 $\textit{p-n}$ junctions, the collection efficiency, $Q$, of electron-hole pairs created by a high-energy electrons flux, e.g. Pm-147 beta flux, is close or equal to 1 in a wide range of electron energies. For SiC junctions, $Q$ is large enough (about 1) only for electrons with relatively low energies of about 5 keV, as 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 obtained for realistic values of the minority carriers' diffusion coefficient and lifetime in Si and SiC $\textit{p-n}$ junctions irradiated by a high-energy electrons flux. Our calculations allow us to estimate the attainable efficiency of betavoltaic elements.