Analysis of Properties of High-Electron--Mobility-Transistor under Optical Illumination

We studied dynamical behaviors of the depletion--mode AlGaAs/GaAs high electron mobility transistor (HEMT) under optical illumination. Photovoltage and the effect of optical generated carries on space charge concentration had been taken into account. Using the chargecontrolling model, we analyzed the optical effect on device's pinch--off voltage, sheet concentration of two dimensional electron gas (2-DEG), I-V characteristic and transconductance as well. Compared with the dark condition, the pinch-off voltage is reduced and the sheet concentration of 2--DEG is increased, which results in an increase in the current gain while the transconductance is insensitive to optical illumination.