TUNNELING OF DIRECT AND INDIRECT EXCITONS IN SLIGHTLY ASYMMETRIC DOUBLE-QUANTUM WELLS

We report the first studies of luminescence spectra from asymmetric do uble quantum wells of GaAs with widths around 100 Angstrom differing b y only one (2.8 Angstrom) or two monolayers. Studies of the position a nd intensity of the direct and indirect exciton lines suggest the exis tence of acoustic phonon-assisted tunnelling between exciton states se parated by a few meV. At temperatures 10-20 K the electron tunnelling process is fast enough to maintain thermal equilibrium between these d irect and indirect excitons which are connected with holes in the same quantum well.