Semiconductor Nanowire Devices for Photovoltaic Photodetection and Photoelectrochemical Applications


Semiconductor nanowires have been successfully utilized as building blocks for various electronic and photonic devices. In particular vertically aligned semiconductor nanowire arrays offer the potential of high photoconversion efficiency compared to that of thin film devices given the nanowire properties of enhanced light absorption improved carrier collection efficiency and reduced optical reflectance. UC San Diego researchers have developed photovoltaic devices and methods to fabricate said devices that utilize semiconductor nanowires with heterojunction photodiode structures to achieve significant device performance gains e.g. broad band spectral response and high energy conversion efficiency. Heterojunctions can be formed by direct epitaxial growth of vertically aligned III-V semiconductor nanowire arrays on their substrate particularly on Si wafer which allows integration of functional III-V-nanowire structures with CMOS technology. The heterojunction bandstructure therein can be engineered by tuning the III-V alloy composition of the nanowires. For example heterojunction photodiode devices formed by InAs nanowire arrays on Si substrate have been operated in photovoltaic mode and found to exhibit a visible-to-infrared photocurrent excitation profile. Heterojunctions can also adopt a coaxial or core-shell configuration i.e. a doped nanowire core surrounded by a shell of complementary doping with multiple quantum wells and superlattice structures being incorporated between the p-type and n-type regions in certain designs. This geometry enables high optical absorption along the long axis of the nanowires while considerably reducing carrier collection distance in the radial direction. The device fabrication methods include embedding the nanowire arrays in polymer matrices and application of transparent conductors as top electrical contacts. Moreover the nanowire semiconductor devices can be implemented as high efficiency photoelectrochemical cells to break down water and CO2 for hydrogen generation and CO2 conversion to fuel respectively. Applications: 1) Photoelectrochemical cells 2) Solar cells

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