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Journal Articles

Defects in GaAs solar cells with InAs quantum dots created by proton irradiation

Sato, Shinichiro; Schmieder, K. J.*; Hubbard, S. M.*; Forbes, D. V.*; Warner, J. H.*; Oshima, Takeshi; Walters, R. J.*

Proceedings of 42nd IEEE Photovoltaic Specialists Conference (PVSC-42) (CD-ROM), 5 Pages, 2015/06

GaAs pn-junction diodes with embedded InAs quantum dots (QDs) are irradiated with protons and the generated deep level traps are investigated using Deep Level Transient Spectroscopy (DLTS). The results are compared to GaAs pn-junction diodes without QDs in order to identify the origin of the deep level traps. The fluence dependence of trap density is investigated, and it is shown that majority carrier traps induced by irradiation increase in proportion to the fluence whereas the EL2 trap, which appears before irradiation, is not affected by irradiation. In addition, minority carrier traps in the QD layer and electron/hole emission from QD levels are investigated by various reverse bias and pulse voltage conditions.

Journal Articles

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

Hubbard, S.*; Sato, Shinichiro; Schmieder, K.*; Strong, W.*; Forbes, D.*; Bailey, C. G.*; Hoheisel, R.*; Walters, R. J.*

Proceedings of 40th IEEE Photovoltaic Specialists Conference (PVSC-40) (CD-ROM), p.1045 - 1050, 2014/06

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 EC-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 EC-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 EC-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.

Oral presentation

Radiation induced defects of III-V solar cells embedded with InAs quantum dots

Sato, Shinichiro; Schmieder, K.*; Hubbard, S.*; Forbes, D.*; Warner, J.*; Oshima, Takeshi; Walters, R.*

no journal, , 

GaAs pn-junction diodes with embedded InAs quantum dots (QDs) are irradiated with high energy protons and the generated deep level traps are investigated using Deep Level Transient Spectroscopy (DLTS). The results are compared to GaAs pn-junction diodes without QDs in order to identify the origin of deep level traps. In addition, the fluence dependence of trap density is investigated and it is shown that traps induced by irradiation increase in proportion to the fluence whereas EL2 trap, which appears before irradiation, is not affected by irradiation.

Oral presentation

Defect levels in GaAs p$$^+$$n diodes embedded with InAs quantum dot layers

Sato, Shinichiro; Schmieder, K.*; Hubbard, S.*; Forbes, D.*; Warner, J.*; Oshima, Takeshi; Walters, R.*

no journal, , 

III-V semiconductor devices embedded with quantum dots (QDs) are expected to be applied to next generation space solar cells. High density QDs and highly stacked QD layers without stacking fault are required in order to relaize QD solar cells, and have been obtained recently by using strain compensating technology. However, larger amount of defects are still incorporated into QD devices compared to single crystal devices and affect the device characteristics. In this study, we fabricated GaAs p$$^+$$n diode with 10 layers of InAs QDs by Metal Organic Vapor Phase Epitaxy (MOVPE) method and characterized defect levels in the devices using Deel Level Transient Spectroscopy (DLTS). The results were compared to reference samples which were GaAs p$$^+$$n diodes without InAs QDs. It was shown that unique electron and hole trap levels were found in the QD devices and thus we concluded that these traps should be reduced in order to improve the device quality.

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