Correlation of Mn lattice location, free hole concentration, and curie temperature in ferromagnetic GaMnAs

摘要

We provide experimental evidence that the electrical and magnetic characteristics of Ga{sub}(1-x)Mn{sub}xAs for a given x depend primarily on the distribution of Mn atoms over their different possible locations in the crystal lattice. Using combined channeling Rutherford backscattering and particle-induced X-ray emission, we show that optimal postgrowth annealing - which leads to an increase of the Curie temperature T{sub}C and is accompanied by an increase of free hole concentration and saturation magnetization - is caused by the reduction in the number of Mn atoms occupying interstitial positions. On the other hand, when Ga{sub}(1-x)Mn{sub}xAs is additionally doped with Be, we observe that - while the hole concentration remains nearly constant - there occurs a strong decrease of T{sub}C together with a dramatic increase in the concentration of Mn interstitials. These results indicate that there is a thermodynamic limit imposed on the maximum Curie temperature in Ga{sub}(1-x)Mn{sub}xAs.