Characterization of ultra-high-speed pseudomorphic AlGaAs/InGaAs (on GaAs) MODFETs

The authors report a detailed characterization of ultrahigh-speed pseudomorphic AlGaAs/InGaAs (on GaAs) modulation-doped field-effect transistors (MODFETs) with emphasis on the device switching characteristics. The nominal 0.1-μm gate-length device exhibit a current gain cutoff frequency (f_t) as high as 152 GHz. This value of f_t corresponds to a total delay of approximately 1.0 ps and is attributed to the optimization of layer structure, device layout, and fabrication process. It is shown that the electron transit time in these very short gate-length devices still accounts for approximately 60% of the total delay, and, as a result, significant improvements in switching speed are possible with further reductions of gate length. The results reported clearly demonstrate the potential of the pseudomorphic AlGaAs/InGaAs MODFET as an ultrahigh-speed device. Its excellent switching characteristics are attributed to the high saturation velocity (~2×10⁷ cm/s), 2DEG sheet density (2.5×10¹² cm^-2), and current drive capability (>200 mA/mm at the peak transconductance)