Cross-sectional scanning tunnelling microscopy was used to study dilute magnetic semiconductors which had been grown by means of low-temperature molecular beam epitaxy. Layers of Ga1-xMnxAs, with x = 0.005, showed that the predominant defect in the material was the As antisite. The Mn ions could also be resolved, and exhibited a signature that was distinct from that of As antisites. Spectroscopic measurements were performed in order to study variations in the Fermi level between Ga0.995Mn0.005As and GaAs layers. The Mn ions acted as acceptor dopants. However, when x was equal to 0.005, the Mn concentration – as compared to the As antisite concentration - was too small to cause a significant movement of the Fermi level away from the mid-gap position. This prevented the layer from being ferromagnetic.

Atomic-Scale Study of GaMnAs/GaAs Layers. B.Grandidier, J.P.Nys, C.Delerue, D.Stievenard, Y.Higo, M.Tanaka: Applied Physics Letters, 2000, 77[24], 4001-3