High performance 0.25 µm p -type Ge/SiGeMODFETs

The authors report the fabrication and characterisation of 0.25 µm 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 µm thick graded Si0.4Ge0.6 buffer. A room temperature hole mobility of 1870 cm2/Vs and a sheet carrier density of 2.1 × 1012 cm–2 were measured. The devices exhibit DC transconductances up to 160 mS/mm and saturation currents up to 300 mA/mm. Cutoff frequencies of fT = 32 GHz and fmax = 85 GHz have been achieved.