  A scattering mechanism stemming from the Stark-shift of energy levels by
electric fields in semiconductor quantum wells is identified. This scattering
mechanism feeds off interface roughness and electric fields, and modifies the
well known 'sixth-power' law of electron mobility degradation. This work first
treats Stark-effect scattering in rough quantum wells as a perturbation for
small electric fields, and then directly absorbs it into the Hamiltonian for
large fields. The major result is the existence of a window of quantum well
widths for which the combined roughness scattering is minimum. Carrier
scattering and mobility degradation in wide quantum wells are thus expected to
be equally severe as in narrow wells due to Stark-effect scattering in electric
fields.
