A complete microwave characterization of GaAs HEMTs under optical illumination

The present paper is devoted at presenting the main results of an extensive experimental investigation of the microwave transistor behaviour under optical illumination. The tested devices are on-wafer HEMTs based on AlGaAs/GaAs heterostructure. The light sensitivity of these transistors is investigated in terms of DC, scattering and noise parameters. The analysis is carried out by observing how the device behaviour changes under CW infrared and visible laser illumination. It is found that the light exposure affects significantly the device behaviour. In particular, the main changes consist of an increase of the drain current, the transconductance, the forward transmission coefficient, and the minimum noise figure. The optical effects have shown to be more pronounced at shorter wavelength. The observed effects of the laser illumination can be ascribed to the threshold voltage shift arising from the internal photovoltaic effect.