Effect of additional nonmagnetic acceptor doping on the Curie temperature and magnetoresistance of Ga1-xMnxAs epitaxial layers

We have investigated the effect of additional doping by Be on the Curie temperature and electrophysical properties of Ga1-xMnxAs (x=0.035). For this relatively low value of Mn concentration the Curie temperature is observed to increase with increasing Be concentration. At low temperatures and in low magnetic fields, a positive magnetoresistance (MR) signal was observed for measurements in the transverse (B I) geometry. However, at high temperatures the MR becomes negative for all fields and all field orientations. The value of the negative MR has a maximum near the Curie temperature, and its magnitude depends strongly on the concentration of free holes. We show that the temperature dependence of the resistivity at zero magnetic field, including the resistivity maximum near the Curie temperature and magnetoresistance, can be successfully described by the magneto impurity scattering model proposed by Nagaev (Phys. Reports 346, 387 (2001)) in both the paramagnetic and the ferromagnetic temperature regions. Quantitative analysis of the experimental data in terms of this model yields the value of the p-d exchange energy |N0β|≅1.6 eV for Ga0.97Mn0.03As. (author)