Defect spectroscopy and non-ionizing energy loss analysis of proton and electron irradiated p-type GaAs solar cells

Abstract

Admittance spectroscopy combined with non-ionizing energy loss (NIEL) analysis is shown to be a powerful tool for analyzing solar cell radiation degradation, not relying on the change of macroscopic cell parameters. GaAs component cells, representative of the middle sub-cell in Ga0.5In0.5P/GaAs/Ge solar cells, were irradiated with protons and electrons in the 0.5–3 MeV energy range. Four irradiation-induced defects are identified in the p-type base layer. The nature of each defect is assessed by analyzing the dependence of its introduction rate on the NIEL deposited by electrons in the semiconductor. The expected linear relationship is only achieved if a unique threshold energy Ed is ascribed to each defect, which ranges from 9 to 38 eV. An electron NIEL with Ed=21eV, customarily used for GaAs-based solar cell degradation analysis, is an approximation of the relative abundance of these four defects. The 21 eV value is thus a GaAs material-specific parameter, independent of the electrical device design. In addition, the type and energy of the incident particle is correlated with the relative abundance of high Ed defects. The impact of each defect on the macroscopic electrical parameters of the cell, namely, the open-circuit voltage VOC, the short-circuit current density JSC, and the recombination current density J02, is assessed with the help of a Pearson analysis. The different effectiveness of electron and proton irradiation on parameters dominated by recombination in the depleted region, such as VOC or J02, is attributed in part to the influence of the particle recoil spectra on the defect capture cross section.