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The transport properties of MnGaAs layers embedded with MnAs clusters have been investigated. It was demonstrated that the presence of MnAs clusters in GaMnAs matrix leads to appearance of photoconductivity and absorption current. These phenomena are related to carrier localization effects at the band bending in the vicinity of the clustermatrix interface.

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Samples of GaMnAs, GaMnAs codoped with Be, and GaMnAs simultaneously codoped with Be and Mg were grown via low-temperature molecular beam epitaxy (LT-MBE). Be codoping is shown to take the Ga sites into the lattice efficiently and to increase the conductivity of GaMnAs. Additionally, it shifts the semiconducting behavior of GaMnAs to metallic while the Mn concentration in the GaMnAs solid solution is reduced. However, with simultaneous codoping of GaMnAs with Be and Mg, the Mn concentration increases dramatically several times over that in a GaMnAs sample alone. Mg and Be are shown to eject Mn from the Ga sites to form MnAs and MnGa precipitates.