  Gate capacitances of back-gated nanowire field-effect transistors (NW-FETs)
are calculated by means of finite element methods and the results are compared
with analytical results of the ``metallic cylinder on an infinite metal plate
model''. Completely embedded and non-embedded NW-FETs are considered. It is
shown that the use of the analytical expressions also for non-embedded NW-FETs
gives carrier mobilities that are nearly two times too small. Furthermore, the
electric field amplification of non-embedded NW-FETs and the influence of the
cross-section shape of the nanowires are discussed.
