OBSERVATION OF A MAGNETIC-FIELD-INDUCED TRANSITION IN THE BEHAVIOR OFEXTREMELY SHALLOW QUANTUM-WELL EXCITONS

Using magnetoabsorption and electroabsorption techniques, we stud exci tons with binding energy comparable to the depth of GaAs/AlGaAs quantu m wells. In-plane magnetic fields decrease the exciton linewidth consi derably. Without magnetic fields, electroabsorption reveals 3D-like ex citon behavior. This broadening persists with magnetic fields along th e growth direction, but changes to a redshift for in-plane magnetic fi elds, reminiscent of 2D-like excitons. We discuss how in-plane magneti c fields change the nature of the exciton by inducing a two-body veloc ity-dependent interaction.