  Si-SiOx superlattices are among the candidates that have been proposed as
high band gap absorber material in all-Si tandem solar cell devices. Due to the
large potential barriers for photoexited charge carriers, transport in these
devices is restricted to quantum confined superlattice states. As a consequence
of the finite number of wells, large built-in fields and any kind of disorder,
the electronic spectrum can deviate considerably from the minibands of a
regular superlattice. In this paper, a quantum-kinetic theory based on the
non-equilibrium Green's function formalism for an effective mass Hamiltonian is
used to investigate photogeneration and transport in such devices for arbitrary
geometry and operating conditions. By including the coupling of electrons to
both photons and phonons, the theory is able to provide a microscopic picture
of indirect generation, carrier relaxation and inter-well transport mechanisms
beyond the ballistic regime.
