  : n-type Ge/SiGe asymmetric-coupled quantum wells represent the building
block of a variety of nanoscale quantum devices, including recently proposed
designs for a silicon-based THz quantum cascade laser. In this paper, we
combine structural and spectroscopic experiments on 20-module superstructures,
each featuring two Ge wells coupled through a Ge-rich tunnel barrier, as a
function of the geometry parameters of the design and the P dopant
concentration. Through the comparison of THz spectroscopic data with numerical
calculations of intersubband optical absorption resonances, we demonstrated
that it is possible to tune by design the energy and the spatial overlap of
quantum confined subbands in the conduction band of the heterostructures. The
high structural/interface quality of the samples and the control achieved on
subband hybridization are the promising starting point towards a working
electrically pumped light-emitting device.
