Ballistic hole injection velocity analysis in Ge UTB pMOSFETs: Dependence on body thickness, orientation and strain

Ge exhibits a high bulk hole mobilty making it an attractive channel material for pMOSFET devices. For improving the device performance and suppressing short channel effects ultra-thin-body (UTB) Ge-on-insulator ( GeOI) structures have been researched throughly. Recently <;110>; oriented Ge-OI pMOSFETs grown on (110) surface were shown to exhibit enhanced hole mobility, which was 3 times compared to (100)/<;100>; Si and 2.3 times (100)/<;100>; Ge pMOSFETs. Due to heavy warping within valence bands and finite atomic granularity in sub-10 nm thick devices, atomistic modelling becomes important. To analyse the recent experimental results a tight binding based 10 band sp3s*d5 (including SO coupling) bandstructure model for is used for UTB Ge. It has been reported in literature that carrier mobility is closely correlated with carrier injection velocity near the top-of-the barrier or the virtual source region. Hence in this paper ballistic injection velocity (vinj) is used as the metric for analysing UTB Ge device performance.