Lattice Expansion of (Ga,Mn)As: The Role of Substitutional Mn and of the Compensating Defects

We apply the density-functional technique to determine the lattice constant of GaAs supercells containing Mn$\text{}_{Ga}$, Mn$\text{}_{int}$, and As$\text{}_{Ga}$ impurities, and use a linear interpolation to describe the dependence of the lattice constant a of Ga$\text{}_{1-x}$Mn$\text{}_{x}$As on the concentrations of these impurities. The results of the supercell calculations confirm that Mn$\text{}_{Ga}$ does not contribute to the lattice expansion. The increase in a is due to both Mn$\text{}_{int}$ and As$\text{}_{Ga}$, that are both created in the as-grown (Ga,Mn)As in proportion to x, and that are most probably present in a remarkable amount also in the best annealed materials.