Postgrowth control of GaAs/AlGaAs quantum well shapes by impurity-free vacancy diffusion

The control of quantum well shapes in GaAs/AlGaAs material after growth has been investigated both theoretically and experimentally. Double quantum well samples capped either by SiO/sub 2/ or fluorides of the group IIA elements were annealed, and energy gap shifts were measured by photoluminescence. These experimental energy shifts were compared to a theoretical model to obtain the diffusion coefficient of aluminum into the quantum wells. Fluorides were found to inhibit the intermixing process almost completely, whereas SiO/sub 2/ is known to enhance it. The aluminum diffusion coefficients for samples annealed at 920/spl deg/C for 30 s are 4.0/spl times/10/sup -17/ cm/sup 2//s and 2.1/spl times/10/sup -15/ cm/sup 2//s for SrF/sub 2/ and SiO/sub 2/ caps, respectively. The activation energies found were 4.09 and 6.40 eV for the same two caps. >