Theory of band-edge optical nonlinearities in type-I and type-II quantum-well structures

A theoretical analysis of the many-body effects in the band-edge absorption spectra of highly excited type-I and type-II semiconductor quantum-well structures is presented. The situation of a homogeneous electron-hole plasma in a usual type-I structure is compared and contrasted to the situation in a type-II structure, where the electron and hole plasmas are spatially separated into adjacent layers. The plasma effects are determined through numerical solutions of a generalized Wannier equation, which accounts for dynamical exchange and screening effects as well as Pauli blocking. In the description of dynamical screening, an alternative to the so-called Shindo approximation is developed. The induced electric-field effects in the type-II systems are investigated by solving the coupled Schrödinger and Poisson equations for the charge carriers.