Nanowire Frontiers: Materials and Devices

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The applicant will develop group III-V semiconductor nanowires (NWs) for three applications - photovoltaics, thermoelectrics and betavoltaics - all related to energy generation. Semiconductor NWs represent a new class of materials that extends the two-dimensional nature of conventional thin film technologies into the third dimension for the next generation of optoelectronic devices. The central challenge in photovoltaic (PV) design is the cost-effective conversion of sunlight to electricity over the very broad range of wavelengths present in the solar spectrum. To overcome the limitations of existing flat panel silicon (Si) PV cells, the applicant is exploiting intentionally engineered III-V semiconductor NWs that can be grown directly on Si solar cells to boost their efficiency. This proposal will continue the applicant's research program on NW PV by using off-axis electron holography to ascertain the doping in NWs, which is one of the key challenges in realizing this technology. While PV devices will efficiently convert visible and near-infrared light into electrical power, the thermoelectric effect can provide a way to convert longer infrared wavelengths into useful electrical energy. During the course of his work on NW-based PV devices, the applicant discovered a new property of semiconductor NWs in their diameter-dependent light trapping properties and highly efficient photo-thermal conversion, which could be very useful for thermoelectric generators (TEGs). In this project, the applicant's ongoing NW PV research will be extended to TEGs using arrays of vertically ordered InSb nanowires, where the thermoelectric efficiency is predicted to be considerably higher compared to existing devices. Finally, betavoltaic (BV) devices use energetic electrons (beta particles) to create electron-hole pairs in a semiconductor by impact ionization for direct generation of electrical power. They are similar to PV devices but replace photons with beta particles, and are therefore a natural extension of the applicant's PV research. We propose to fabricate gallium phosphide (GaP) NWs on Si substrates for improved BV batteries by offering a higher efficiency of beta capture and larger voltage than equivalent Si BV devices. A significant benefit arises from likely commercialization of this research - in particular, development of nanodevices that might yield advantages for future energy technologies. This proposal is an opportunity for Canada to be the first in the world to develop disruptive technologies that will yield a competitive edge in large markets. This proposal will also provide a unique training opportunity for young researchers wishing to establish careers in the Canadian optoelectronics industry where a continual supply of highly qualified personnel (HQP) is needed.