The damage that was produced at GaAs/Al0.6Ga0.4As/GaAs interfaces, in samples which had been subjected to implantation with 1MeV Kr+ ions at 77 or 293K, was investigated by using ion channelling and transmission electron microscopic techniques. The low-temperature ion-channelling spectra which were obtained from samples that had been implanted at 77K to a dose of 1014/cm2 were similar to the random spectrum; thus indicating that the GaAs and AlGaAs layers had suffered a considerable amount of damage. An asymmetrical signal appeared in the He+ ion-channelling spectrum as the sample was warmed to room temperature. The back-scattering yield which corresponded to the bottom interface (AlGaAs on GaAs) resembled the random yield, whereas that from the top interface (GaAs on AlGaAs) decreased and shifted towards the unirradiated channelling spectrum. This suggested that the damage which was produced at the top of the AlGaAs layer was thermally unstable. Cross-sectional transmission electron microscopic images revealed a larger amount of damage, in the form of extended defects and amorphous regions, at the bottom interface than at the top one. This difference was sufficient to account for the observed asymmetry in the channelling spectra. It was found that increasing the dose, to 1015/cm2, produced a damaged state throughout the AlGaAs layer that was stable at both 77 and 293K. Transmission electron microscopic examination revealed that, at this dose, the GaAs and AlGaAs layers were both amorphous. Room-temperature implantation to a dose of 1016/cm2 was also carried out, and planar defects were observed at both interfaces; although their density appeared to be greater near to the bottom interface. The latter was also rougher than the top interface. The difference in the damaged states at the bottom and top interfaces was attributed to a variation in the number of displacement cascade events as a function of depth through the AlGaAs layer. This variation in the number of cascades resulted in the occurrence of differing amounts of ion mixing at the top and bottom interfaces.

B.A.Turkot, D.V.Forbes, I.M.Robertson, J.J.Coleman, L.E.Rehn, M.A.Kirk, P.M.Baldo: Journal of Applied Physics, 1995, 78[1], 97-103