The photoresponse of microwave HEMTs: semi-analytical modeling

This paper is concerned with the response of HEMTs transistors to optical excitation. An experimental evaluation was conducted and a model was developed. The results indicate that the dominant photodetection mechanism is the internal photovoltaic effect (backgating), caused by the accumulation of photogenerated holes in the GaAs buffer layer. Accordingly, the effect of illumination is equivalent to a shift in the gate to source bias point and characterized by a nonlinear photocurrent-optical power relationship. The device exhibits an extremely high quantum efficiency at low optical intensities, but the bandwidth is limited to the MHz range. It is suggested that an additional terminal at the substrate would increase the bandwidth while retaining significant gain over conventional photodiodes