Optical EngineeringEnhanced optical effect in a high-electron-mobility phototransistor device: two-dimensional modeling considering a realistic velocity-field relation
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An enhanced optical effect is observed in a high electron mobility transistor device when the radiation is allowed to fall on the gaps of the source, gate, and drain of a n-AlGaAs/GaAs system. A 2-D model is presented considering a realistic velocity field relation of carriers in the n-AlGaAs layer. Due to the incident radiation, a photovoltage is developed across the heterojunction in addition to band-edge discontinuity between the n-AlGaAs and GaAs layers. This photovoltage drags the electrons from the n-AlGaAs layer into the heterointerface, thus significantly enhancing the sheet concentration of 2-D electron gas. The drain current and transconductance of the device increase considerably. Plots have been made for the I-V characteristics and the transconductance versus gate voltage. Also, a ratio of drain current under illumination and drain current under a dark condition has been plotted against the input optical power density, which indicates that the overall gain of the device is enhanced by a factor of more than 10 compared to its dark case.