EXCITED 2S STATE OF A DONOR CONFINED IN A GAAS ALXGA1-X AS QUANTUM-WELL/

A spectroscopic study of the shallow Si donor and its bound exciton (B E) confined in narrow GaAs/AlxGa1-xAs quantum wells (QW's) has been pe rformed. The electronic structure has been investigated by means of se lective photoluminescence and photoluminescence excitation spectroscop y. The energy separation between the ground state and the excited stat e of the confined Si donor has been monitored by means of two-electron transitions (TET's) of the confined-donor BE. It is concluded in this study that the TET satellite originates from the ls-2s transition, in contrast to the bulk case, where the 1s-2p+/- and 1s-2p0 donor transi tions are also strong. The energy position of the observed TET satelli te yields a value for the ls -2s energy separation of 10.6 meV for a d onor in the center of a 100-angstrom-wide QW, which is in excellent ag reement with recent theoretical predictions. The interpretation of the observed TET satellite as being due to the 1s-2s transition is also s upported by the magnetic-field dependence.