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HL: Fachverband Halbleiterphysik

HL 46: Poster 2

HL 46.32: Poster

Donnerstag, 29. März 2007, 15:00–17:30, Poster A

InGaAs/GaAsSb tunnel junction in an InP(100)-based low band gap tandem solar cell — •Ulf Seidel, Erol Sagol, Ulrike Bloeck, Klaus Schwarzburg, and Thomas Hannappel — Hahn-Meitner-Institute, Glienicker Str. 100, 14109 Berlin, Germany

III-V multi-junction (m-j) solar cells are currently the most efficient PV devices worldwide. In a m-j solar cell multiple absorbers with different band gaps are connected in series. At present, the world record m-j solar cell was epitaxially grown lattice-matched to GaAs(100) or rather to Ge(100). Regarding the highest theoretical efficiencies there is a lack of an appropriate material with a band gap in the range of 1eV. Therefore, a monolithic low band gap tandem solar cell on the lattice constant of InP(100) was designed with band gaps regarding a 4- or 5-junction solar cell. It can be combined with a high band gap tandem or triple cell via different techniques. The lattice-matched InGaAs (E_g = 0.73 eV) was utilized for the lowest band gap absorber and also lattice-matched InGaAsP for the absorber material around 1 eV. The two sub cells were connected by a new tunnel junction including n-InGaAs and p-GaAsSb. With regard to the sharpness of the InGaAs/GaAsSb interface, we investigated the growth of the GaAsSb layer on different InGaAs surface reconstructions in-situ with reflectance difference spectroscopy (RDS) and in ultra high vacuum with X-ray PES (XPS) and LEED. A significant difference was measured for the Sb to As surface stoichiometry at the GaAsSb layer, indicating that the more established growth of GaAsSb on an As-rich InGaAs surface resulted in a too low Sb-content in the first monolayers of GaAsSb.