Back-illuminated GaAs OPFET: A High Visible/UV Contrast Photodetector

We report high Ultraviolet (UV) rejection under UV-visible illumination in GaAs Optical Field Effect Transistor (OPFET) or optically-controlled Metal-Semiconductor Field Effect Transistor (MESFET) when the device is back-illuminated by inserting a fiber upto the active layer-substrate interface. This is attributed to the difference in the absorption coefficient of GaAs in the UV and the visible regions with the device back-illuminated; in-depth analysis is provided in the paper. The results are based on theoretical model accounting for photoconductive and photovoltaic effects. We structurally optimize the GaAs OPFET device for visible/UV contrast photodetector applications considering two different gate materials (Gold (Au) and Indium-Tin-Oxide (ITO)). The visible responsivity and the dark current have also been considered for optimization.