Local structure about Mn atoms in In1-xMnxAs diluted magnetic semiconductors

X-ray-absorption fine-structure measurements were performed at the Mn K edge on In0.88Mn0.12As diluted magnetic semiconductors prepared by molecular-beam epitaxy. It has been found that in the high-growth-temperature samples (Ts=280°C), Mn atoms are primarily incorporated in the form of MnAs clusters with NiAs structure. No significant disorder is observed. In the low-growth-temperature samples (Ts=210°C), the majority of Mn atoms form small (r∼3 A), disordered, sixfold-coordinated centers with As. The presence of disorder in MnAs centers for the latter case is established using the method of cumulants. Only a very small fraction of Mn atoms may substitute for In in the zinc-blende InAs structure. Effective valency and coordination of Mn atoms deduced from the near-edge structure are the same for both the high- and low-growth-temperature In1-xMnxAs films. The formal valency is lower than +3. The local structures established in the present work are consistent with the observed difference in magnetic behavior for samples prepared at different substrate temperatures.