Electronic effects determining the formation of ferromagnetic III 1-xMnx V alloys during epitaxial growth

Magnetic properties of III_1-xMn_1-xV 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 III_1-xMn_xV 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 III_1-xMn_1-x.V alloys with Be, as well as remote Be-doping (modulation doping) of Al_1-yGa_yAs/Ga_1-xMn _x.As/Al_1-yGa_yAs heterostructures. © 2004 Eisevier B.V. All rights reserved.