Berlin 2005 – wissenschaftliches Programm

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DS: Dünne Schichten

DS 22: Optische Spektroskopie dünner Schichten II

DS 22.7: Vortrag

Dienstag, 8. März 2005, 16:00–16:15, TU HS110

Photoluminescence Excitation Spectroscopy of highly compensated CuGaSe₂ — •Susanne Siebentritt, Alexander Zajogin, Niklas Rega, and Martha Lux-Steiner — Hahn-Meitner-Institut, Glienicker Str. 100, 14109 Berlin

The interest in CuGaSe₂ is twofold: it is an attractive absorber material for thin film tandem solar cells and it shows a unique behaviour concerning its native defects, which have very low formation enthalpies, concerning its phase behaviour and its grain boundaries. The material used in solar cells is grown under Cu-poor conditions. Previous work has shown that this material is highly compensated and shows spatial potential fluctuations. To investigate these fluctuations the absorption of the band tails needs to be measured. Since grain boundary free material today can only be obtained by epitaxy on GaAs no transmission spectroscopy is possible. Therefore the band tail absorption and its overlap with luminescence is investigated by PLE (photo luminescence spectroscopy). From the overlap the amplitude of the fluctuations is determined to at least 70 meV. The absorption spectra obtained by PLE depend strongly on the detection wave length. This is due to the fact that different detection wave lengths probe different depths of the fluctuations. Interestingly the same effect has been observed in CuGaSe₂ grown under Cu excess where no potential fluctuations are expected. A critical review of PLE as a measure for the absorption will be given together with a comprehensive analysis of the potential fluctuations in CuGaSe₂.