Damage accumulation, and subsequent thermally activated annealing reactions, in AlAs layers on GaAs substrates were studied by using X-ray diffraction techniques. Irradiation with 2.5MeV electrons was performed at 4.6K, up to a total dose of 2 x 1019/cm2. By measuring irradiation-induced changes in the lattice parameter, it was possible to obtain information concerning the properties of interstitial atoms and vacancies in AlAs for the first time. For instance, the observed value of the lattice expansion was affected by the defect concentration, c, and the relaxation volumes of interstitials, Vi, and vacancies, Vv; according to: relative lattice change = c(Vi + Vv)/3Ω, where Ω was the average atomic volume. These results exhibited remarkable similarities to those for GaAs. The irradiation-induced increase in the lattice parameter amounted to some 50% of the change which was observed in the GaAs substrates. Separation of the defect concentration and relaxation volume of the Frenkel pair was not possible on the basis of the lattice parameter data alone. Nevertheless, the increase in lattice constant indicated that interstitials, which were expected to have a positive relative volume, predominated over vacancies; which could have smaller negative values of the relaxation volume. By assuming that the relaxation volume of the Frenkel pair was equal to 1Ω, the defect concentration was deduced to be equal to 1019/cm3. A comparison of the relaxation volumes for GaAs, InP, Si and Ge, indicated that the value of 1Ω was a maximum value; which yielded a minimum value for the defect concentration. Because of the observed absolute magnitude of the relative lattice change, it was concluded that Frenkel pairs in AlAs were characterized by large distortion fields which could be frozen in, in large quantities, at low temperatures. A major annealing step occurred near to room temperature, rather continuous annealing occurred at up to 500K, and a final recovery stage was found between 700 and 900K. There was no indication of an unusually high defect mobility, as no significant annealing occurred below 250K. It was suggested that the broad annealing stage (250 to 500K) might have some fine structure which was not resolved here but might correspond to the I, II and III stages which were observed in GaAs (due to the migration of various types of interstitials). Consequently, the final annealing stage was attributed to the migration of vacancies. The temperature of the final annealing stage, and previous data, suggested that it was related to the melting point.

A.Gaber, H.Zillgen, P.Ehrhart, P.Partyka, R.S.Averback: Journal of Applied Physics, 1997, 82[11], 5348-51