Influence of the Dynamic Access Resistance in the g{sub}m and f{sub}T Linearity of AlGaN/GaN HEMTs

摘要

The decrease of transconductance g{sub}m and current gain cutoff frequency f{sub}T at high drain current levels in AlGaN/GaN high-electron mobility transistors (HEMTs) severely limits the linearity and power performance of these devices at high frequencies. In this paper, the increase of the differential source access resistance r{sub}s, with drain current is shown to play an important role in the fall of g{sub}m and f{sub}T. The increase of r{sub}s occurs due to the quasi-saturation of the electron velocity in the source region of the channel at electric fields higher than 10 kV/cm. This has been confirmed by both experimental measurements and two-dimensional drift-diffusion simulations. Through simulations, we have identified HEMT structures with source implanted regions (or n{sup}(++) cap layers) as good candidates in order to increase the linearity of the g{sub}m and f{sub}T versus current profile.