Electronic effects determining the formation of ferromagnetic III1-xMnxV alloys during epitaxial growth

Magnetic properties of III1-xMnxV ferromagnetic alloys depend critically on the distribution of Mn++ ions over the different sites which this ion can occupy in the host III-V lattice. The reason for this is that only Mn++ ions at substitutional group-III sites, Mn-III, provide both the localized spins and (since they are acceptors) also the free carriers needed to mediate the ferromagnetic interaction between these spins. Mn++ ions occupying interstitial sites, on the other hand, are double donors, which compensate the substitutional Mn acceptors, thus reducing the hole concentration; and, in addition, the Mn interstitials form antiferromagnetic pairs with the substitutional Mn++ ions, thus canceling their magnetic moments. Both these effects result in lowering the Curie temperature of the III1-xMnxV alloys. In this paper we show that the manner in which Mn enters the III-V lattice is determined by the Fermi level (i.e., by the electronic processes within the material) during the growth process itself. To demonstrate this, we describe a series of growth experiments that involve annealing, co-doping of III1-xMnxV alloys with Be, as well as remote Be-doping (modulation doping) of Al1-yGayAs/Ga(1-x)Mn(x)AS/Al1-yGayAs heterostructures. (C) 2004 Elsevier B.V. All rights reserved.