Analysis of radiation damaged and annealed gallium arsenide and indium phosphide solar cells using deep level transient spectroscopy techniques

Abstract

Degradation of solar cell performance from radiation damage was found to be reversed through annealing processes. The mechanisms behind the degradation and recovery is based on deep-level traps, or defects, in the lattice structure of the solar cell. Through a process known as Deep Level Transient Spectroscopy (DLTS) a correlation can be made between damage/recovery and trap energy level/concentration of the cell. Gallium arsenide (GaAs) and Indium phosphide (InP) solar cells were subjected to 1 MeV electron irradiation by a Dynamitron linear acceleration at two fluence levels of 1E14 and 1E15 relectrons/cm(2) The process of annealing included thermal annealing at 90 degrees C with forward bias current and thermal annealing alone (for GaAs). After each cycle, DLTS measurements were taken to determine the energy level of the traps and their concentration. Multiple cycles of irradiation, annealing and DLTS were performed to observe the correlation between degradation and recovery to trap energy level and concentration. The results show that the lower energy level traps are associated with the recovery of the cells while the higher level traps are associated with the overall permanent degradation of the cells. Applying this information to future research could allow for significant increases in satellite mission life and potentially increase mission payload.