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HL: Halbleiterphysik

HL 42: Photovoltaik II

HL 42.1: Vortrag

Freitag, 30. März 2001, 11:30–11:45, S6

Electronic defect spectroscopy in the Cu(In, Ga)(S,Se)₂ chalcopyrite system — •Mircea Turcu, Immo Koetschau, Uwe Rau, and Hans Werner Schock — Institut fuer Physikalische Elektronik, Pfaffenwaldring 47, 70159 Stuttgart

The contribution presents investigations of electronic defects in the Cu(In,Ga)(S,Se)₂ chalcopyrite system and their dependence on alloy composition. We prepare Cu-poor thin films by coevaporation of the elements under high vacuum conditions. The films have a Ga/(In+Ga)-ratio close to 0.3 and S/(S+Se) ratio varying in the range between 0 and 0.9. Heterojunctions are prepared via chemical bath deposition of CdS, sputter deposition of ZnO and evaporation of an Al-metal contact grid. We analyse the effect of S/Se substitution on the electronic defect levels by means of photoluminescence and admittance spectroscopy. The activation energy of shallow defect levels observed by photoluminescence is constant when the S/Se ratio is varied. In contrast, as the S/(S+Se) ratio increases we find that the deep acceptor level generally observed by admittance spectroscopy shifts towards higher energies and the overall defect density increases at the same time. With the help of quantum efficiency measurements we scale the alignment of the band edges of the respective absorber films relative to the bulk defect level. With this method we derive the evolution of the band diagram with increasing S content in the Cu(In,Ga)(S_xSe_1−x)₂ system.