Impact of nanostructures and radiation environment on defect levels in III–V solar cells

Baseline and quantum dot (QD) GaAs pn-junction diodes were characterized by deep level transient spectroscopy before and after both 1MeV electron irradiation and 140 keV proton irradiation. Prior to irradiation, the addition of quantum dots appeared to have introduced a higher density of defects at E
C
-0.75 eV. After 1 MeV electron irradiation the well-known electron defects E3, E4 and E5 were observed in the baseline sample. In the quantum dot sample after 1 MeV electron irradiation, defects near E3, E4 and E
C
-0.75 eV were also observed. Compared to the irradiated baseline, the QD sample shows a higher density of more complex E4 defect and a lower density of the simple E3 defect, while the E
C
-0.75 eV defect seemed to be unaffected by electron irradiation. As well, after proton irradiation, well known proton defects PR1, PR2, PR4' are observed. The QD sample shows a lower density PR4' defects and a similar density of PR2 defects, when compared to the proton irradiated baseline sample.