High-frequency SiGe-n-MODFET for microwave applications

n-type SiGe modulation-doped hetero field-effect transistors (MODFET's) with a 0.25-mu m Schottky-gate on a Si0.55Ge0.45 buffer are presented. The layer structure was designed to enable elevated sheet carrier densities of n(s) = 7.0 x 10(12) cm(-2) at moderate electron mobilities of 1050 cm(2)/Vs. Reducing the thickness of the cap layers enhances the control of the gate on the 2DEG and leads to a high transconductance of 320 mS/mm, Targeting analog applications we focused on large current densities around 400 mA/mm, Due to advanced RF-characteristics the 100-GHz hurdle of f(max) was passed for the first time with f(max)(U) = 120 GHz and Si was determined at 42 GHz.