FREE AND ACCEPTOR-BOUND EXCITONS IN THE TRANSITION REGION BETWEEN 2-DIMENSIONAL AND QUASI-3-DIMENSIONAL GAAS ALXGA1-XAS SYSTEMS

The transition from a two-dimensional to a quasi-three-dimensional electron system has been studied in multiple quantum wells, by varying the barrier thickness L(b) for a constant 100-angstrom well width. Dramatic differences in electron-hole correlation are observed due to the different extension of electron and hole wave functions. The 1S-2S energy separation of the heavy-hole exciton decreases from 8.3 meV for L(b) = 150 angstrom to 3.1 meV for L(b) = 10 angstrom. The acceptor-bound-exciton binding energy is constant, while the bound-exciton decay time increases dramatically with decreasing L(b).