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High gain-bandwidth product and visible/UV contrast photodetectors are vital in Visible Light Communication (VLC) and Ultraviolet (UV) reflectance imaging applications respectively. We adopt material and structural optimization to perceive such photodetectors with back-illuminated Optical Field Effect Transistor (OPFET) wherein any potential difference in absorption coefficient of the semiconductor material between the visible and the UV range (higher in the UV region) can be explored at its full potential. The results have been analyzed using the photoconductive and the photovoltaic effects, the series resistance effects, scaling rules-induced effects, and channel length-variation effects. We consider the three most prominent and functional materials in the visible range (Si, GaAs, and InP) for material-based optimization. Structural optimization is performed employing a range of medium gate lengths. The gate electrodes utilized are Indium-Tin-Oxide (ITO) for Si and GaAs with high Schottky barrier heights of ~0.71 eV and ~0.98 eV respectively whereas the Schottky contact on InP is gold (Au) with a high barrier height of ~0.8 eV. The operating visible and UV wavelengths are 600 nm and 350 nm respectively. The results suggest that GaAs OPFET has wide bandwidth potential in the gigahertz range apart from its high sensitivity and visible/UV contrast features. The InP-based OPFET exhibits high sensitivity and sub-gigahertz frequency response; and can compete or surpass the GaAs OPFET in terms of the visible/UV contrast ratio. The Si OPFET shows bandwidth in the megahertz range along with high sensitivity but exhibits low contrast ratio. The structural parameters have a significant effect on the detector response. The results are in-line with the experiments. This paper reflects the performance of the investigated detectors towards the said applications through optimization and the associated analysis represents the dependence of the obtained response on the device material and structural parameters, thus, opening the door for further research.

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