High performance 0.25μm p-type Ge/SiGe MODFETs

The authors report the fabrication and characterisation of 0.25 mu m gate length p-type Ge channel modulation doped field effect transistors (MODFETs) with improved RF performance. The structure consists of a compressively strained pure Ge hole channel, grown on a relaxed 5 mu m thick graded Si0.4Ge0.6 buffer. A room temperature hole mobility of 1870cm(2)/Vs and a sheet carrier density of 2.1 x 10(12)cm(-2) were measured. The devices exhibit DC transconductances up to 160mS/mm and saturation currents up to 300mA/mm. Cutoff frequencies of f(T) = 32GHz and f(max) = 85GHz have been achieved.