Frequency dispersion and modulated signal distortion characteristics of gaas power MESFETs at large signal operation

Abstract

AbstractIn the search for a cause of modulated signal distortion of a GaAs power FET, an analysis is made for the frequency dispersion caused by the surface trap. First, the frequency dispersion characteristics of the Vgs‐Id relationship of the FET under a large signal operation are measured. It is found that the Vgs‐Id characteristics at high frequencies are very different from the one at dc. It is found that the drain current decreases near Vgs = 0 V. Further, simulation is carried out for the intermodulation distortion using the Vgs‐Id characteristics at the high‐frequency region. It is found that an increase in the nonlinearity of the Vgs‐Id characteristic due to frequency dispersion is the cause of increased modulated signal distortion. From the measured temperature dependence of the frequency dispersion of the drain current, energy levels related to the dispersion are found to be 0.56 and 0.19 eV. Further, a comparison is made between SiN and SiO2 surface passivation films. It is found that frequency dispersion is small and a low distortion characteristic can be obtained with the SiN film.