The effects of low-temperature annealing and oxidation of the dilute magnetic semiconductor ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$ are studied by photoemission spectroscopy in the hard x-ray regime (HAXPES), with special attention to the depth profile of both concentration and chemical state of manganese. Annealing of ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$ in air at $190°\text{C}$ for up to 150 h leads to an enrichment of manganese at the surface accompanied by an increase in the native oxide layer. These observations are consistently explained by thermally activated surface segregation of interstitial Mn and its subsequent passivation by oxidation, thereby confirming a recently suggested mechanism for an enhancement of the Curie temperature upon annealing.

• Received 19 December 2007

DOI:https://doi.org/10.1103/PhysRevB.78.075319