Abstract:
A tight-binding version of the coherent-potential approximation is used to describe the electronic structure of Ga_1-xMn_xAs mixed crystals with variable degree of co-doping. Both donors and acceptors are considered to control the number n of free carriers. The mean-field value of the Curie temperature T_c is estimated from the energy required to reverse one local moment. T_c/x is shown to scale as a function of n/x, with only a minor influence of the actual chemical composition, and discuss the character of the exchange coupling in various doping regimes.
We also address the self-compensation in (Ga,Mn)As. We find that the substitutional and interstitial positions of Mn are in a dynamical equilibrium and are realized in proportion approx. 3:1 also in a wide range of concentrations of Mn.