Thermal annealing study of radiation induced defects in nitride-based multi- junction solar cell structures using Deep Level Transient Spectroscopy

DLTS analysis of radiation-induced defects in p-type GaInNAs and GaNAs solar cell structures are presented. The DLTS spectra of GaInNAs indicates one dominant electron emitting trap E1 (0.30 eV) and three-hole emitting traps H1 (0.27 eV), H2 (0.33 eV) and H3 (0.67 eV). Also, one dominant electron emitting trap E2 (0.20 eV) and two-hole emitting traps H4 (0.28 eV) and H5 (0.60 eV) were observed in GaNAs. After 1 MeV electron irradiation, the concentrations of E1, H1, H2, H3, and H5 increase significantly. The concentration of E2 decreases significantly and H4 decreases partially. Thermal annealing study shows the complete annealing of E1 and E2, and the significant decrease in concentrations of H2, H3, H4 and H5, whereas H1 increases in concentration. It is observed that GaNAs shows more radiation-resistance than GaInNAs and the possibility of using this material as the third-junction in high-efficiency four-junction solar cells for space applications appears to be very promising.