TRANSFORMATION OF THE DIMENSIONALITY OF EXCITONIC STATES IN QUANTUM-WELLS WITH ASYMMETRIC BARRIERS IN AN ELECTRIC-FIELD

A transformation of the dimensionality of excitonic states from 2D to 3D with increasing external electric field is observed in single GaAs/ AlxGa1-xAs quantum-well structures with asymmetric barriers. The bindi ng energy of a 2D exciton remains constant over a wide range of variat ion of the field, since the decrease in the binding energy is compensa ted by increasingly larger penetration of the electronic wave function into the barrier layer, where the exciton binding energy is higher be cause the effective mass is larger and the dielectric constant of AlGa As is lower than that of GaAs. When the maximum of the electron wave f unction is displaced into the barrier as the field increases, the exci ton binding energy decreases. As the field increases further, a 2D exc iton transforms into a quasi-3D exciton, with a heavy hole in the quan tum well and an electron in a resonant above-barrier state. (C) 1998 A merican Institute of Physics.