Nanowire arrays are intensively studied in view of third generation solar cells applications. Specifically, III-V nanowires are attractive due to their excellent optoelectronic properties as high mobility of the carriers and light emission. These nanowires however suffer from surface parasitic effects. Core-shell nanowire heterostructures reduce these effects and provide many advantages to such as band-gap engineering, antireflective properties and piezoelectric effects due to lattice mismatch of the materials. The critical parameters for an efficient solar cell based on nanowires are the nanowire diameter, height, distance between nanowires and the array’s symmetry. In this thesis we study GaAs-InGaAs core-shell nanowire heterostructures for photovoltaic applications. The nanowire samples were grown on Si (111) by Ga-assisted molecular beam epitaxy via the vapor-liquid-solid mechanism. Scanning electron microscopy images were taken in order to study the diameter, the height, density and the parasitic 2D layer in between nanowires on the interface with the substrate. The optical characterization of the samples was accomplished with photoluminescence measurements versus temperature. Subsequently, solar cell devices based on the nanowire samples were fabricated. After fabrication, SEM images were taken again in order to measure the density of the protruding nanowires as only these are important for the carrier collection. The final characterization of the nanowire solar cells was achieved by I-V and spectral quantum efficiency measurements.
(EN)
University of Crete
