Electrical characteristics of an optically controlled N-channel AlGaAs/GaAs/InGaAs pseudomorphic HEMT

Electrical characteristics of an n-channel Al/sub 0.3/Ga/sub 0.7/As/GaAs/In/sub 0.13/Ga/sub 0.87/As pseudomorphic HEMT (PHEMT) with L/sub g/=1 μm on GaAs are characterized under optical input (P/sub opt/). Gate leakage and drain current have been analyzed as a function of V/sub GS/, V/sub DS/, and P/sub opt/. We observed monotonically increasing gate leakage current due to the energy barrier lowering by the optically induced photovoltage, which means that gate input characteristics are significantly limited by the photovoltaic effect. However, we obtained a strong nonlinear photoresponsivity of the drain current, which is limited by the photoconductive effect. We also proposed a device model with an optically induced parasitic Al/sub 0.3/Ga/sub 0.7/As MESFET parallel to the In/sub 0.13/Ga/sub 0.87/As channel PHEMT for the physical mechanism in the drain current saturation under high optical input power.