Gate-to-drain separation and transistor cutoff frequency in wet etched AlGaN/GaN HFETs

The variation of cutoff frequency f_T with gate-to-drain separation L_GD in 0.2 μm gate AlGaN/GaN HFETs fabricated by low-damage isolation techniques is studied. The transistor delay τ_T = 1/2πf_T increases linearly with L_GD due to the rise in drain resistance with increasing L_GD. The resulting apparent gate-drain resistance is higher than the post-process low-field value, and is dependent upon the fabrication process for devices implemented on the same layers, probably reflecting different levels of surface damage