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 binding energy of a 2D exciton remains constant over a wide range of variation of the field, since the decrease in the binding energy is compensated by increasingly larger penetration of the electronic wave function into the barrier layer, where the exciton binding energy is higher because the effective mass is larger and the dielectric constant of AlGaAs is lower than that of GaAs. When the maximum of the electron wave function is displaced into the barrier as the field increases, the exciton binding energy decreases. As the field increases further, a 2D exciton transforms into a quasi-3D exciton, with a heavy hole in the quantum well and an electron in a resonant above-barrier state. (C) 1998 American Institute of Physics.