Effect of the location of Mn sites in ferromagnetic Ga1-xMnxAs on its Curie temperature -: art. no. 201303

We report a strong correlation between the location of Mn sites in ferromagnetic Ga1-xMnxAs measured by combined channeling Rutherford backscattering and by particle-induced x-ray emission experiments and its Curie temperature. The concentrations of free holes determined by electrochemical capacitance-voltage profiling and of uncompensated Mn2+ spins determined from superconducting quantum-interference device magnetization measurements are found to depend on the concentration of unstable defects involving highly mobile Mn interstitials. This leads to large variations in T-C of Ga1-xMnxAs when it is annealed at different temperatures in a narrow temperature range. The fact that annealing under various conditions has failed to produce Curie temperatures above similar to110 K is attributed to the existence of an upper limit on the free hole concentration in low-temperature-grown Ga1-xMnxAs.