Si/SiGe FETs grown by MBE on a LEPECVD grown virtual substrate

This paper reports on the preparation and assessment of Si/SiGe based n-type field-effect transistors (n-FET). The layer growth was carried out in a two step epitaxy procedure. First, a strain-relieved SiGe layer with a final Ge fraction of 40% was deposited on a Si(100) wafer by means of low energy plasma enhanced chemical vapor deposition (LEPECVD). On this virtual substrate the active layer stack was grown by molecular beam epitaxy (MBE) consisting of a 9 nm thick strained Si channel sandwiched between Sb modulation doped Si0.6Ge0.4 cladding layers. The samples were structurally analyzed by atomic force microscopy (AFM), X-ray diffraction (XRD), and cross-section transmission electron microscopy (XTEM). FET structures were prepared and electrically characterized by conductivity and Hall measurements and by recording DC characteristics. Electron Hall mobilities as high as 760 cm2 V−1 s−1 at a carrier density of 7.6×1012 cm−2 has been obtained at room temperature (RT). A maximum transconductance of 230 mS mm−1 and a drain saturation current of 230 mA mm−1 have been achieved.