Magnetotransport in ferromagnetic pn-diode of (Ga,Mn)As and (Ga,Mn)N

Here we have demonstrated a large magnetoresistance in tunnelling (Ga,Mn)As/GaAs diodes at low temperatures.The (Ga,Mn)As and (Ga,Mn)N pn-diodes were fabricated by using Molecular Beam Epitaxy (MBE).Firstly, heavily doped n+-GaAs was grown on top of n-type GaAs substrate. After that the magnetic Mn doped GaAs layer with different Mn concentrations was grown by MBE. The growth temperature was only 230 C in order to inhibit formation of secondary phases and segregation of Mn at the surface. Finally, the ohmic contacts were evaporated by an electro-beam evaporator. The structure of the (Ga,Mn)N pn-diode was similar, except the fact that the n-and p-type areas were in the opposite order. In addition, the n-type magnetic layer (Ga,Mn)N was made by solid state diffusion of Mn inside the MBE chamber. The direct magnetization measurements were performed in order to confirm that the (Ga,Mn)As and (Ga,Mn)N layers are ferromagnetic. However, no magnetic field dependence in the diode current was observed in the I-V characteristics of the pn-diodes, which were made of Mn doped GaAs or GaN and which had a lightly doped n-side.