Interdiffusion of Al and Ga in heavily C-doped Al o . 3 Ga O . 7 As/GaAs supeduttice (SL) structures has been investigated quantitatively for a variety of ambient and surface encapsulation conditions. High-resolution photoluminescence (PL) at T = L 7 K was employed to evaluate the extent of layer intermixing after 24-h anneals at 825°C. From the shifts to higher energies of the PL peaks due to n = 1 e1ectron-to-heavy hole transitions in the quantum wells of the annealed SLs relative to the posi.tion of this peak in the as-grown crystal, approximate AI-Ga interdiffusion coefficients (D Al-Cia) have been determined for different annealing conditions. For all encapsulants studied the interdiffusion in C-doped crystals is accelerated with increasing AS 4 pressure in the annealing ampoule. This result disagrees with previously observed trends for Group II-doped p-type structures, which have led to the charged point-defect model (Fermi-level effect) of AI-Ga interdiffusion. The Si~\ N4 cap has provided the most effective surface sealing against ambient-stimulated layer interdiffusion, and yielded D A1 _ Ga ~ 1.5 -3.9X 10-19 cm 2 /s. The most extensive layer intermixing has occurred for uncapped SL annealed under As-rich ambient (D A1 -Ga ~3.3 X 10-]8 cm 2 /s). These values are up to -40 times greater than those previously reported for nominally un doped AlxGa1_xAs/GaAs SLs, i.mplying that the CAS doping slightly enhances host-atom selfdiffusion on the Group III sublattice, but significantly less than predicted by the Fermi-level effect. The discrepancies between the experimental observations and the model, are discussed. 5615 J.

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Degradation in optical and electrical properties has been observed for high-purity and high-mobility p-type GaAs layers which contain significant concentrations of an unidentified shallow acceptor-like defect, labeled “A”, that is frequently incorporated in crystals grown by molecular beam epitaxy. Low-temperature photoluminescence and variable temperature Hall-effect measurements were employed to monitor the aging process in samples stored for about one year at room temperature. Profound changes in the exciton recombination spectra, indicative of increasing concentration of the “A” defect, have been accompanied by a decrease in hole mobility and an increase in carrier concentration. These results are discussed in the context of the acceptor-pair defect model, originally proposed by Eaves and Halliday [J. Phys. C: Solid State Phys. 17, L705 (1984)].

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