Effect of p-type buffer layer on the properties of GaMnAs ferromagnetic semiconductors

We have studied the magnetic and transport properties of Ga _1-xMn _xAs epilayers grown either on undoped or on p-type doped GaAs buffer layer. The temperature dependence of the resistivity at zero magnetic field reveals that the Curie temperature (T _C) in the Ga _1-xMn _xAs layer grown on p-type doped GaAs buffer is slightly higher than that observed in the layer grown on undoped GaAs buffer. The magnetic and transport properties of the two samples show significant differences when they are placed in a magnetic field. In SQUID measurements, the Ga _1-xMn _xAs layer grown on p-type buffer shows a larger coercive field and much slower decay of remanent magnetization than the layer grown on undoped buffer. This robust magnetic behavior observed in the doped sample is discussed in terms of the increase of free carrier concentration in the system arising from p-type doping in the buffer layer.