The migration of ion-implanted Be was studied as a function of Al concentration. The behavior of Be in AlGaAs was similar to that in GaAs, and it even exhibited the anomalous characteristic of increased redistribution with decreasing temperature. The results could be described by:

Ga0.8Al0.2As:     D(cm2/s) = 1.8 x 10-9 exp[-0.90(eV)/kT]

Ga0.6Al0.4As:     D(cm2/s) = 3.3 x 10-9 exp[-0.84(eV)/kT]

GaAs:     D(cm2/s) = 8.9 x 10-10 exp[-1.00(eV)/kT]

The diffusivity of Be appeared to increase with Al content. This was suggested to be due to an increase in the bond strength of matrix atoms upon adding Al. This prevented the easy transfer of Be from interstitial to substitutional sites. An over-saturation of Be interstitials could also explain the persistence of anomalous diffusion in AlGaAs with respect to the annealing temperature. The results were explained in terms of a substitutional-interstitial diffusion mechanism, the relative amounts of interstitial and substitutional Be, and the relative difficulty of moving from an interstitial to a substitutional site.

C.C.Lee, M.D.Deal, J.C.Bravman: Applied Physics Letters, 1995, 66[3], 355-7