Stability and diffusion of interstitital and substitutional Mn in GaAs of different doping types

We report on the lattice location of Mn impurities (< 0.05%) in undoped (semi-insulating) and heavily $n$-type doped GaAs, by means of $\beta^{-}$-emission channeling from the decay of $^{56}$Mn produced at ISOLDE/CERN. In addition to the majority substituting for Ga, we locate up to 30% of the Mn impurites on tetrahedral interstitial sites with As nearest neighbors. In line with the recently reported high thermal stability of interstitial Mn in heavily $p$-type doped GaAs [L. M. C. Pereira et al., Appl. Phys. Lett. 98, 201905 (2011)], the interstitial fraction is found to be stable up to 400$^{\circ}$C, with an activation energy for diffusion of 1.7–2.3 eV. By varying the concentration of potentially trapping defects, without a measurable effect on the migration energy of the interstitial impurities, we conclude that the observed high thermal stability is characteristic of isolated interstitial Mn. Being difficult to reconcile with the general belief that interstitial Mn is the donor defect that out-diffuses at ∼200$^{\circ}$C, these findings motivate a careful reassessment of the structural effects of low temperature annealing of Ga$_{1−x}$Mn$_{x}$As, with potential implications on the prospects for achieving higher Curie temperatures.