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Tandem solar cells composed of several stacked structures are being studied to obtain higher device efficiencies. We are in the process of develop a tandem solar cell by stacking a normal p-GaAs/n-GaAs structure to convert the visible part of the solar spectrum, and a p-InGaAsSb/n-GaSb heterostructure to use the infrared portion of the spectrum and improve the solar cell efficiency. For this purpose we have grown p-type InGaAsSb layers on top of n-type Te-doped GaSb substrates using the liquid phase epitaxy growth technique. P-type doping was achieved using Zn pieces as a dopant in the melt growth, and adjusting the growth temperatures to obtain high crystalline quality InGaAsSb epilayers. A series of Zn-doped InGaAsSb quaternary layers were grown varying the Zn concentration in the layer to get p-n heterojunctions with different characteristics. The crystalline quality of the InGaAsSb layers was proved by using low temperature photoluminescence (PL) spectroscopy to characterize the exciton-related emission bands which gave us a semi-quantitatively evaluation of the layer quality, and of the presence of defects and the Zn-related PL emissions. Using microRaman spectroscopy we also analyzed the crystalline quality at the microscopic level having found good quality homogeneity in the layer surface identifying the several combinations of phonon modes present. The quality of the interface layer-substrate was studied using the photoacoustic (PA) technique in the open-cell configuration and measuring the frequency dependence of the PA phase signal; from the theoretical analysis of this dependence we were able to obtain values for the interface non-radiative recombination times, and so, to assess the quality of the interface which will play a crucial role in determining the ultimate efficiency of the tandem solar cell. |