Effects of Be-Codoping on the Properties of GaMnAs Films Grown via Low-Temperature Molecular Beam Epitaxy

Be-codoped GaMnAs layers were systematically grown via low-temperature molecular beam epitaxy with varying Mn and Be fluxes. Two Be fluxes to exhibit semiconducting and metallic resistivities were chosen, and the Mn fluxes were controlled so as to cover the range from solid solutions to precipitates. The structural, electrical, and magnetic properties were investigated for the as-grown and the annealed structures. Both the lightly and the heavily Be-codoped GaAs:(Mn,Be) films revealed ferromagnetism at room temperature due to precipitates of MnAs and MnGa. Beryllium preferably took the Ga sites through competition with Mn, and the pushed-out Mn atoms formed precipitates. Heavy codoping of Be, as well as heat treatments, facilitated the precipitation of MnGa rather than MnAs. The anomalous Hall-resistance originating from the precipitates was observed at room temperature only in the degenerately Be-codoped metallic GaAs:(Mn,Be) films. The observation was assisted by the high conductivity of the GaAs:Be matrix.