We report on high-resolution x-ray diffraction measurements of (Ga,Mn)As and (Ga,Mn)(As,P) epilayers. We observe a structural anisotropy in the form of stacking faults that are present in the (111) and (11$\overline{1}$) planes and absent in the ($\overline{1}$11) and (1$\overline{1}$1) planes. They occupy ${10}^{-2}\%$–${10}^{-1}\%$ of the ferromagnetic epilayer volume while no stacking faults are detected in the controlled, undoped GaAs epilayer. Full-potential density functional calculations provide additional evidence that the formation of the stacking faults is promoted by Mn attracted to these structural defects. The enhanced Mn density along the common [1$\overline{1}$0] direction of the stacking fault planes produces a symmetry-breaking mechanism of a strength and sense that can account for the uniaxial [110]/[1$\overline{1}$0] magnetocrystalline anisotropy of these ferromagnetic semiconductors.

• Received 13 April 2011

DOI:https://doi.org/10.1103/PhysRevB.83.235324