Nonlinear Optical Properties of GaAs/(AlGa) As Multiple Quantum Wells Under Quasistationary High Laser Excitation and Transversal Electric Fields

We use the pump and probe beam and the luminescence spectroscopy to study the nonlinear response of GaAs/(AlGa)As heterostructures to quasistationary excitation conditions. The carrier induced energetic shift of the 1hh-exciton as a function of the quantum well width shows a dimensional dependence of the carrier screening properties. This shift gives a rather good criterion to decide if a system behaves more 2D or 3D like. The high excitation regime is dominated by electron-hole plasma features. Many particle effects lead to a renormalization of the fundamental bandgap. This effect is essential for understanding the physics of III–V semiconductor lasers. The carrier density and the reduced bandgap are determined via systematic evaluation of both gain and luminescence spectra. The observed behaviour can be described by a strict 2D theory using effective exciton parameters in order to account for the finite well widths of the structures. The study of the higher sub-bands reveals that both, exciton bleaching and sub-band renormalization are mainly due to direct occupation of the specific sub-band while intersub-band effects are considerably smaller. By coating the two sides of a 50×l00Å multiple quantum well with semitransparent Cr-Au electrodes we are able to control the energetic position of the 1hh-exciton as a function of the applied electric field and of the incoming light power. Several structures to optimize this effect in order to build an electrooptical switch or modulator are discussed.