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Optimization of growth conditions of type-II Zn(Cd)Te/ZnCdSe submonolayer quantum dot superlattices for intermediate band solar cells

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5 Author(s)
Dhomkar, Siddharth ; Department of Physics, Queens College, CUNY, Flushing, New York 11367 and The Graduate Center, CUNY, New York, New York 10016 ; Kuskovsky, Igor L. ; Manna, Uttam ; Noyan, I.C.
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Intermediate band solar cells (IBSCs) have been predicted to be significantly more efficient than the conventional solar cells, but have not been realized to their full potential due to the difficulties related to the fabrication of practical devices. The authors report here on growth and characterization of Zn(Cd)Te/ZnCdSe submonolayer quantum dot (QD) superlattices (SLs), grown by migration enhanced epitaxy. These QDs do not exhibit formation of wetting layers, which is one of the culprits for the unsatisfactory performance of IBSCs. The ZnCdSe host bandgap is ∼2.1 eV when lattice matched to InP, while the Zn(Cd)Te-ZnCdSe valence band offset is ∼0.8 eV. These parameters make this material system an excellent candidate for a practical IBSC. The detailed structural analysis demonstrates that the process of desorption of Cd and the preferential incorporation of Zn facilitates the formation of unintentional strained ZnSe-rich layer at the QD-spacer interface. The growth conditions have been then optimized so as to obtain high crystalline quality lattice matched SL, by growing intentionally Cd-rich spacers, which strain balanced the SL. The excitation intensity dependent photoluminescence confirmed the type-II nature of these multilayer QD structures, which is expected to suppress nonradiative Auger recombination, and improve the carrier extraction process when implemented in an actual device.

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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures  (Volume:31 ,  Issue: 3 )