GaAs FET Channel Structure Investigation using MBE

The effects of channel profile and structure on Gm linearity, Gm/Cgs ratio, and the output resistance of GaAs FETs were investigated through the use of molecular beam epitaxy (MBE). An impulse type doping profile was used to fabricate a GaAs FET and found to give very linear Gm resulting in a 15 dB improvement in second-harmonic distortion as compared to our standard ion implanted profile. Channel layers with differing doping concentrations were grown to study doping effects on the Gm/Cgs ratio. GaAs FETs with different gatelength (L) to channel depth (a) ratios (L/a) were fabricated with channel structures which incorporated P-N sub-channel dipole layers or AlGaAs and GaAs buffer layers to investigate mechanisms affecting the drain output resistance Rd. Substantial increases in output resistance are achieved through channel modification.