Carrier concentration and mobility profiling in quantum wells by scanning probe microscopy

Charge transport at nanoscale in ultra-scaled semiconductor structures and specifically designed nano-standards is investigated by different scanning probe microscopy (SPM) methods, i.e. scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM). A set of dedicated samples, containing B doped Si/Si0.75Ge0.25/Si quantum wells (QWs) with different thickness ranging from 20 to 1 nm and with B doping ranging from 1 × 1018 cm−3 to 5 × 1018 cm−3 were grown by molecular beam epitaxy. We demonstrated that the combined application of SCM and SSRM, commonly used to measure the local carrier concentration and the resistivity, respectively, allows to determine other physical properties, like the drift mobility in the nanometer thick QWs. Interesting effects were directly observed at nanoscale, like the relevant decrease in hole mobility with the shrinkage of QWs width from 20 to 1 nm, which was explained by the increasing role of surface scattering at the Si/SiGe interface for thinner QWs.