Binding energies of excitons and donors in a double quantum well in a magnetic field

We study binding energies of both excitons and donors in a symmetric double quantum well in the presence of a magnetic field applied parallel to the growth direction. We express wave functions as combinations of Gaussian-type orbitals and subband wave functions of even and odd parities, with variationally determined expansion parameters. By varying the interwell barrier width and well sizes (hence varying the interwell coupling), we obtain binding energies ranging in character from that for a strongly coupled double well to that for a system of two isolated single wells. The behavior of the binding energies as function of the interwell coupling, well sizes, and the magnetic field, as well as the donor position is consistently described with our formalism with naturally included subband mixing effects. The magnetic field leads to stronger confinement of the wave functions and enhances binding energies.