Magnetoresistance of Ga1-xMnxAs epitaxial layers doped by Be

Magnetoresistance (MR) measurements were performed on Ga1-xMnxAs (x = 0.03) additionally doped with Be. At low temperatures and in low magnetic fields, a positive MR signal was observed for measurements in the transverse (B perpendicular to 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. The observed MR behavior can be described by the magnetoimpurity scattering model in both the paramagnetic and the ferromagnetic temperature regions. Quantitative analysis of the Ga1-xMnxAs MR data yields the value of the p-d exchange energy as \N0beta\ approximate to 1.6eV.