Extremely high transconductance Ge/Si_0.4Ge_0.6 p-MODFET's grown by UHV-CVD

Ge-channel modulation-doped field-effect transistors (MODFET's) with extremely high transconductance are reported. The devices were fabricated on a compressive-strained Ge/Si0.4Ge0.6 heterostructure with a Hall mobility of 1750 cm2/Vs (30,900 cm2/Vs) at room temperature (77 K). Self-aligned, T-gate p-MODFET's with Lg = 0.1 μm displayed an average peak extrinsic transconductance (gmext) of 439 mS/mm, at a drain-to-source bias voltage (Vds) of -0.6 V, with the best device having a value of gm(ext) = 488 mS/mm. At 77 K, values as high as gm(ext) = 687 mS/mm were obtained at a bias voltage of only Vds = -0.2 V. These devices also displayed a unity current gain cutoff frequency (fT) of 42 GHz and maximum frequency of oscillation (fmax) of 86 GHz at Vds = -0.6 V and -1.0 V, respectively.