Detailed defect study in proton irradiated InP/Si solar cells

A detailed study of the effects of proton irradiation-induced defects in heteroepitaxially grown InP/Si solar cells has been made through a combination of cathodoluminescence (CL), electron beam induced current (EBIC), and electrochemical capacitance versus voltage (ECV) carrier profiling measurements. The CL data indicate the distribution of nonradiative recombination centers both before and after proton irradiation, and temperature dependent and spectroscopic analysis of the CL signal give an estimate of the energies of the dominant defect levels. The EBIC data yield an estimate of the magnitude and spatial variation of the minority carrier diffusion length $\mathrm{(L)}$ in the base region. Values of L determined from EBIC measurements made on solar cells irradiated by protons ranging in energy from 0.1 up to 4.5 MeV follow a single curve when plotted versus displacement dose, $D_d,$ allowing a single proton damage coefficient to be determined. The ECV measurements show the evolution of the carrier concentration profile in the cell under irradiation, as carrier removal first depletes and eventually type converts the base region. From an in-depth analysis of the combined data, the physical defects that give rise the radiation-induced energy levels are suggested, and a detailed understanding of the physical mechanisms causing the radiation response of InP/Si solar cells is developed.