Electronic states inGa1−xMnxAs:Substitutional versus interstitial position of Mn

By using spin-polarized full potential linearized augmented plane wave method we obtained the electronic structure of (Ga,Mn)As crystals with Mn in substitutional, interstitial, and both positions. It is shown that the interstitial Mn acts as a double donor and compensates the holes created by two Mn atoms in substitutional positions. This explains why the number of holes in ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ is usually much smaller than x. The effective Mn doping efficiency is simply related to the proportion of substitutional and interstitial Mn and does not depend on x provided that the proportion is fixed. The calculated local electronic structure of the substitutional and interstitial Mn differ appreciably, so that the x-ray L emission spectra can be used to distinguish the two positions of Mn.