Time resolved measurement of interface and bulk recombination of solar cell materials

We have investigated the effect of different metal organic vapor phase epitaxy (MOVPE) preparation routes for the In
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Ga
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As/InP interface on the interface recombination velocity and its lateral interface homogeneity. The preparation routines in a MOVPE reactor were varied in order to initiate a lateral homogenous layer growth and to form the In-GaAs/InP interface as sharp as possible, which is of major importance for the performance of thin device structures such as tunnel junctions in multi junction solar cells. For the growth characterization, we employed in situ reflectance difference/ anisotropy spectroscopy and low energy electron diffraction to depict the favorable interface formation routes. Minority carrier lifetime dependence in a corresponding InP/InGaAs/InP double hetero structure was measured with spatially resolved and time-resolved photoluminescence using a confocal single photon counting setup. It was found that a specific, III-rich termination of the underlying InGaAs layer was most favorable for optimum results.