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, MnIII, 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/Ga1−xMnxAs/Al1−yGayAs heterostructures.