Influence of non-random incorporation of Mn ions on the magnetotransport properties of Ga_1-xMn_xAs alloys

Abstract

We study theoretically the influence of a spatially nonrandom incorporation of Mn ions on the magnetotransport in paramagnetic Ga1–xMnxAs alloys. Such a nonrandomness may be introduced during post-growth annealing treatment. We use a resistor-network model for describing the electrical transport of this disordered semiconductor system as a function of temperature and external magnetic field. The model is founded on classical semiconductor band-transport and neglects many-body interactions. The peculiarities of paramagnetic dilute magnetic semiconductors, in particular, the magnetic-field induced changes of the density of states, the broad acceptor-energy distribution, and the interplay of magnetic field independent disorder (due to the alloying of GaAs with Mn) and magnetic field dependent disorder (due to the the Giant Zeeman splitting) are accounted for in a mean-field fashion. We have previously shown that this empirical transport model based on reasonable assumptions and realistic material parameters yields a satisfactory quantitative description of the experimentally obtained temperature and magnetic-field dependence of the resistivity of Ga0.98Mn0.02As samples annealed at different temperatures. For Ga1–xMnxAs alloys annealed at temperatures above 500 °C where structural changes lead to the formation of MnAs clusters, the transport is dominated by the paramagnetic GaAs:Mn host matrix as the cluster density is below the percolation threshold. We will show that in this situation the transport results can only be explained accounting for a nonrandom Mn distribution. Thus the analysis shown here provides further understanding of the annealing-induced changes of the transport properties in dilute magnetic III-Mn-V semiconductors.