Analysis of microwave noise parameters of scaled AlGaAs/GaAs HEMT's under light exposure

In this work, the results of an extensive experimental analysis of on wafer AlGaAs/GaAs HEMT's under CW visible laser exposure are presented. The DC and 2-26.5 GHz small-signal performances of scaled gatewidth (100, 200, 300 μm) with and without illumination have been deeply investigated and compared with the results previously reported in the literature. In addition, the noise parameter variations in the 2-18 GHz range have been analyzed. The observed effects exhibit a marked dependence from the light exposure especially in terms of the minimum noise figure and the optimum noise reflection coefficient. The effects of the laser illumination are clearly related to a threshold voltage shift, due to the internal photovoltaic effect, which resulted to be the predominant response process related to CW optical power absorption. As a general trend, the light sensitivity has shown to be more pronounced in the smallest device for either DC and microwave (scattering and noise) parameters.