Investigations on fundamental properties/issues of nanowires/structures with applications in solar cell, energy storage, and sensing devices.

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Nanostructures can be used as fundamental elements in manufacturing many devices. Among them, nanostructures made of silicon and zinc oxide, ZnO, with significant physical properties have been the focus of research for a variety applications. Silicon nanowires, besides having many applications in electronic and optoelectronics, are used to fabricate the new generation of sustainable energy devices, such as solar cells. An array of silicon nanowires SiNWs, beside having excellent light antireflection properties, provide opportunities to design light trapping and carrier collection processes independently. Also semiconductor ZnO has been the focus of research for many applications for the last several years because the material is nontoxic, chemically stable, and biocompatible with a direct wide bandgap, strong ionic bonding, and exciton binding energy 60 meV. Despite the significant promises offered by these nanostructures, there are still several challenging issues related to physical properties of these elements; for example, in the case of SiNW solar cells, surface and interface recombination, surface roughness, mechanical and chemical stability, surface morphology, doping control, integration with other modules, and device packaging are some of these issues. In the case of ZnO, in many applications well-distributed and highly oriented NWs are of crucial importance. Furthermore, controllable fabrications of p-type or n-type ZnO NWs are the key for applications in nano optoelectronic devices since, p-type ZnO NWs exhibit a band gap reduction and strong acceptor-related photoluminescence and the n-type NWs have band gap broadening with a strong donor-bound exciton. Therefore, preparing cost-effective and high quality of these nanowires, for any specific application on a large scale and with high throughput, is considered to be very challenging task. The general scope of this proposal is the design, fabrication, and characterization of arrays of silicon and ZnO semiconductor nanowires/nanostructures for various applications. Works will be focused on research and investigations on the fundamental issues related to structures, physical properties, and fabrication of nanostructures with applications in photonics, energy, and sensing devices. The low cost of the developed technique is considered as an important factor. Finally, we design and fabricate devices based on the most promising elements produced in this work; our focus will be on developing a gas ionization sensor (GIS) and photovoltaic devices based on the nanowires/structures grown in this proposal. Therefore, in this proposal the following two main objectives will be studied: 1) Investigating methods to grow low cost but high quality with large throughput of zinc oxide and silicon nanowires. The techniques should enable us to control the morphology, size, aspect ratio, and conductivity of these nanostructures during the growth. Issues like doping, orientation, distribution, and uniformity of the array of nanowires will be addressed. 2) Developing devices based on the generated nano structures described in the first objective. A gas ionization sensor as well as PV devices will be designed and fabricated using the ZnO and silicon nanowires. The possibility of applying these structures for the purpose of hydrogen storage will be investigated. This proposal will have significant impact on reducing our environmental pollutions in two ways: first by developing PV devices to generate clean and renewable energy, and secondly, by developing a miniaturized GIS to detect pollutant gases.