Carrier Dynamics Investigation on Passivation Dielectric Constant and RF Performance of Millimeter-Wave Power GaN HEMTs

The effect of the passivation layer dielectric constant and T-gate geometry on the performance of millimeter-wave high-power GaN HEMTs is investigated through a nanoscale carrier dynamics description obtained by full-band cellular Monte Carlo simulation. The effective gate length is found to be increased by fringing capacitances and enhanced by the dielectric constant of the passivation layer in the regions adjacent to the gate for layers thicker than about 5 nm. Detailed simulation results are shown for the carrier energy, velocity, scattering, and electric field profiles along the channel. The output impedance under small- and large-signal operations is also discussed. Our results indicate that the effect of the passivation layer dielectric constant changes the nanoscale carrier dynamics and can strongly affect the radio-frequency performance of deep submicrometer devices.