Photovoltaic and Betavoltaic Efforts at University of Missouri-Columbia
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Photovoltaic device converts solar energy into electricity by the photovoltaic effect. Efficiency of a photovoltaic device depends on the active material which absorbs light as well as the window layer which transmits light into the active layer. High band gap window layer allows majority of light to transmit from the solar spectrum while active layer has an optimum value for maximum efficiency. We have carried out research on amorphous silicon as an active conversion layer which has a larger band gap and higher light sensitivity than crystalline Si for photovoltaic device, while high band gap zinc oxide (ZnO) can serve as window layer. Betavoltaic device is analogous in principle to a photovoltaic and the difference is that it is specifically designed to convert energy from beta particles rather than photons. Nano crystalline silicon-carbide (SiC) and ZnO are some of the ideal candidates for betavoltaic devices because of its high band gap and radiation hardness. Both of them are also sensitive to light, so potentially they can be used to fabricate photovoltaic devices. Present betavoltaic devices based on SiC are not cost effective as SiC requires high temperature process. We were able to achieve SiC films at a low temperature process by converting amorphous SiC into crystalline SiC using aluminum induced crystallization technique. The films were characterized by FTIR, TEM, UV-Vis spectroscopy, Hall measurements and I-V measurements. The p-n junctions are fabricated by depositing p-type SiC layer on n-type substrates. For successful fabrication of betavoltaic device, high quality n-ZnO films are deposited and characterized by Raman spectroscopy, XRD, UV-Vis spectroscopy, Hall measurements, I-V and photoconductivity measurements. ZnO based p-n junctions are fabricated by depositing ZnO (n-type) layer on p-type Si substrate, and the rectifying behaviors were observed. For proof of concept a betavoltaic device was fabricated and tested with beta particle.