Transport study of the annealing‐induced transition from Ga_1−xMn_xAs alloys to GaAs:Mn/MnAs hybrids

The magneto‐resistance properties of a Ga_0.98Mn_0.02As alloy grown by molecular beam epitaxy and corresponding GaAs:Mn/MnAs hybrid samples obtained by controlled thermal annealing at different temperatures between 350 and 600 °C were studied. Thermal annealing at first leads to a non‐randomness of the Mn distribution within the alloy and at higher temperatures finally to the formation of mesoscopic MnAs clusters within the surrounding GaAs:Mn matrix. The change in the transport behavior can be modelled realistically using a network model based on activated transport and accounting for the magnetic properties of the Ga_1−xMn_xAs matrix and the MnAs clusters. Comparison of experiment and theory shows that the modification of the magneto‐transport properties due to annealing is dominated by changes of the Ga_1−xMn_xAs matrix, i.e. reduction of x. The number of the MnAs clusters formed is too small to considerably influence the transport.