Berlin 2005 – scientific programme

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DS: Dünne Schichten

DS 22: Optische Spektroskopie dünner Schichten II

DS 22.6: Talk

Tuesday, March 8, 2005, 15:45–16:00, TU HS110

Potential fluctuations in compensated Cu(In,Ga)Se₂ - A photoluminescence study — •Niklas Rega, Susanne Siebentritt, Juergen Albert, and Martha Lux-Steiner — Hahn-Meitner-Institut Berlin, Glienicker Str. 100, D-10405 Berlin

Cu(In,Ga)Se₂ is a compound semiconductor which belongs to the family of chalcopyrites. They are interesting materials for application(solar cells achieve efficiencies of 19.5%) and a fascinating topic for fundamental investigations due to their unique phase and defect behaviour. Intrinsic defects are doping the chalcopyrite. Therefore metal organic vapour phase epitaxy is used for the growth to ensure good composition control.
High efficiency Cu(In,Ga)Se₂ solar cells are fabricated under Cu-poor conditions, i.e. [Cu]/([Ga]+[In]) < 1. The photoluminescence (PL) spectra of CuGaSe₂ and CuInSe₂ films grown under Cu-poor conditions are characterized by a broad asymmetric luminescence. Temperature and power dependent PL measurements show that the broadening of luminescence is due to a donor-acceptor-pair (DAP) transition in the presence of locally fluctuating potentials due to compensation. Here we present a PL study on Cu-poor grown epitaxial Cu(In,Ga)Se₂-layers with varying [Ga]-content. The aim of this contribution is the quantification of the potential fluctuations in dependence of the [Ga]-content. The depth of the fluctuating potentials is estimated. For CuGaSe₂ we get a mean depth of 70meV and for CuInSe₂ of 20meV. The influence of fluctuations in the [Ga]-content, which causes a fluctuation of the band gap energy, has to be taken into account for Cu(In,Ga)Se₂.