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

Abstract

Baseline and quantum dot (QD) GaAs pnjunction 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 wellknown 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.

Characterization of nonradiative recombination centers in proton-irradiated InAs/GaAs quantum dots by two-wavelength-excited photoluminescence

“…The performance of solar cells on spacecraft, however, degrades with the irradiation of high-energy particles such as protons and electrons. [7][8][9] Since the performance degradation is caused by the increase in the number of radiation-induced defects, which act as nonradiative recombination (NRR) centers in active layers, the effect of such irradiation on the defect distribution should be clarified. Recently, it has been reported that the PL efficiency of InAs=GaAs QDs enhances from low to intermediate fluences but quenches at higher fluences for InGaAs=GaAs and InAs=GaAs QDs without strain balancing layers.…”

“…8,10,11) Experimental results on radiation-induced defects in InAs= GaAs QDs are based on the results of deep-level transient spectroscopy (DLTS), including a recent systematic characterization of electron and hole trap levels with a GaP strain balancing layer. 7,9) DLTS requires us to prepare a suitable Schottky contact or an appropriate p-n junction for measurement. Besides DLTS, another complementary study is desirable to reinforce the distribution of native defects as well as irradiation-induced defects in InAs=GaAs QD structures in order to realize high-efficiency IBSCs.…”