Superlattices of Ga0.7Al0.3As/GaAs which had been grown by means of metalorganic chemical vapor deposition, and which were heavily doped with C using CCl4, were annealed (825C, 24h) under various ambients and encapsulants. Photoluminescence monitoring at 1.7K was used to determine approximate interdiffusion coefficients, DAl-Ga, for various annealing conditions. For all of the encapsulants which were studied, DAl-Ga increased with increasing As4 pressure in the annealing ampoule. This result disagreed with trends which had been reported for Mg-doped crystals, and with the predictions of the charged point-defect (Fermi-level) model. It was noted that a Si3N4 cap provided the most effective surface protection against ambient-stimulated layer interdiffusion (DAl-Ga = 1.5 x 10-19 to 3.9 x 10-19cm2/s). The most extensive layer intermixing occurred for uncapped superlattices which were annealed in an As-rich ambient (DAl-Ga equal to about 3.3 x 10-18cm2/s). These values were up to 40 times greater than those which had previously been reported for nominally undoped AlGaAs/GaAs superlattices. This implied that doping slightly enhanced layer intermixing; but this was significantly less than that predicted by the Fermi-level effect. The discrepancies between the experimental data and the model were considered. Marked changes in the optical properties of the annealed superlattices, as a function of storage time at room temperature, were also reported. It was suggested that these changes might reflect a degraded thermal stability of the annealed crystals, due to lattice defects which were generated at high temperatures. It was proposed that this was related to the failure to prepare buried heterostructure quantum-well lasers, via impurity-induced layer disordering, in similar doped crystals.

I.Szafranek, M.Szafranek, J.S.Major, B.T.Cunningham, L.J.Guido, N.Holonyak, G.E.Stillman: Journal of Electronic Materials, 1991, 20[6], 409-18