  The use of low-dimensional structures such as quantum wells, wires or dots in
the absorbing regions of solar cells strongly affects the spectral response of
the latter, the spectral properties being drastically modified by quantum
confinement effects. Due to the microscopic nature of these effects, a
microscopic theory of absorption and transport is required for their
quantification. Such a theory can be developed in the framework of the
non-equilibrium Green's function approach to semiconductor quantum transport
and quantum optics. In this paper, the theory is used to numerically
investigate the density of states, non-equilibrium occupation and corresponding
excess concentration of both electrons and holes in single quantum well
structures embedded in the intrinsic region of a p-i-n semiconductor diode,
under illumination with monochromatic light of different energies. Escape of
carriers from the quantum well is considered via the inspection of the spectral
photocurrent at a given excitation energy. The investigation shows that escape
from deep levels may be inefficient even at room temperature.
