Dresden 2009 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 1: III-V semiconductors I

HL 1.2: Talk

Monday, March 23, 2009, 10:30–10:45, BEY 81

Minority carrier lifetime of MOCVD grown InGaAsP and InGaAs absorbers for low bandgap tandem solar cells — •Nadine Szabo, Erol Sagol, Marinus Kunst, Klaus Schwarzburg, and Thomas Hannappel — Helmholtz Zentrum Berlin Glienicker Str. 100 14109 Germany

MOVPE-grown III-V semiconductor compounds are implemented in today's state-of-the-art third generation multi-junction solar cells. Conventional triple-junction solar cells grown on germanium, having Ge, Ga(In)As and GaInP as subcells, reached a record efficiency of 40.7%. This could be improved further if the Ge subcell is replaced by a double junction solar cell. The best bandgap combination was found out to be 0.7 eV and 1 eV. These bandgaps could easily be realized with materials such as InGaAs and InGaAsP which are lattice-matched to InP. The lifetime of minority charge carriers in these absorber materials is essential for the performance of solar cells. Time resolved photoluminescence (TRPL) and transient microwave conductivity (TRMC) measurements were used to evaluate the lifetime of the absorber materials grown in a double hetero-structure. To get meaningful results, a precise knowledge of the excess carrier density created by the pump pulse is necessary. With our single photon counting TRPL setup a carrier density regime between 10E9 cm-3 and 10E16 cm-3 in the VIS (λ<1000 nm) and 10E13 cm-3 and 10E16 cm-3 in the NIR (λ<1700 nm) can be assessed. We will present the lifetime of minority carriers in p-InGaAs and p-InGaAsP layers for different thicknesses as a function of excitation density.