  The 3D- and 2D- behaviour of wide parabolic PbTe single quantum wells, which
consist of PbTe p-n-p-structures, are studied theoretically and experimentally.
A simple model combines the 2D- subband levels and the 3D-Landau levels in
order to calculate the density of states in a magnetic field perpendicular to
the 2D plane. It is shown that at a channel width of about 300nm on can expect
to observe 3D- and 2D-behaviour at the same time. Magnetotransport experiments
in selectively contacted Hall bar samples are performed at temperatures down to
T = 50 mK and at magnetic fields up to B = 17 T.
