Radiation Response of n-Type Base InP Solar Cells

The effects of particle irradiation on the electrical properties of high efficiency p/n InP solar cells have been studied using a variety of techniques including current-voltage and spectral quantum efficiency measurements (QE), electron beam induced currents (EBIC), and deep level transient spectroscopy. A detailed analysis of the radiation response of the solar cell photovoltaic response is presented, and the primary damage mechanisms are identified. Data measured after irradiation by protons of various energies are correlated in terms of displacement damage dose to produce a characteristic degradation curve for the p/n InP technology. This characteristic curve is compared to that of the n/p InP technology to provide an assessment of the relative radiation hardness of the p/n devices. Radiation-induced decreases in the minority carrier diffusion length in both the p-type emitter and n-type base at low damage levels have been extracted from the QE and EBIC measurements, and damage coefficients have been determined. At high damage levels, EBIC profiles suggest that the primary device degradation mechanism is an increase in bulk resistivity due to electron trapping in the base. However, capacitance-voltage measurements did not indicate any change in the junction capacitance. A model to account for these effects based on radiation-induced defect kinetics is presented.