Low-temperature magnetotransport behaviors of heavily Mn-doped (Ga,Mn)As films with high ferromagnetic transition temperature

We report the low-temperature magnetotransport behaviors of (Ga,Mn)As films with the nominal Mn concentration x larger than 10%. The ferromagnetic transition temperature TC can be enhanced to 191 K after postgrowth annealing (Ga,Mn)As with x=20%. The temperature Tm, corresponding to the resistivity minimum in the curve of resistivity versus temperature at temperature below TC, depends on Mn concentration, annealing condition, and magnetic field. Moreover, we find that the variable-range hopping may be the main conductive mechanism when temperature is lower than Tm.