Comparative study of self-aligned and nonself-aligned SiGe p-metal–oxide–semiconductor modulation-doped field effect transistors with nanometer gate lengths

A self-aligned process used to fabricate p-type SiGe metal–oxide–semiconductor modulation-doped field effect transistors (MOS-MODFET) is described. Self- and nonself-aligned p-type Si0.2Ge0.8/Si0.7Ge0.3 MOS-MODFETs with gate-lengths from 1 μm down to 100 nm were fabricated. The dc and microwave characteristics of these devices are presented. In comparison with nonself-aligned devices, self-aligned devices exhibited higher extrinsic transconductances, lower threshold voltages, higher unity current gain cutoff frequencies fT, and maximum oscillation frequencies fMAX. Self-aligned MOS-MODFETs with a gate length of 100 nm exhibited an extrinsic transconductance of 320 mS/mm, an fT of 64 GHz, and an fMAX of 77 GHz. To our knowledge, these are the highest data ever reported for any MOS-type p-FETs with a SiGe channel. All these excellent performances were measured at very low drain and gate biases.