Nanometer-scale studies of point defect distributions in GaMnAs alloys

Gleason, J. N.; Hjelmstad, M. E.; Dasika, V. D.; Goldman, R. S.; Fathpour, S.; Charkrabarti, S.; Bhattacharya, P. K.
January 2005
Applied Physics Letters;1/3/2005, Vol. 86 Issue 1, p011911
Academic Journal
We have investigated the concentrations and distributions of point defects in GaMnAs alloys grown by low-temperature molecular-beam epitaxy, using ultrahigh-vacuum cross-sectional scanning tunneling microscopy (XSTM). High-resolution constant-current XSTM reveals “A,” “M,” and “V” defects, associated with AsGa, MnGa, and VAs, respectively. A and V defects are present in all low-temperature-grown layers, while M defects are predominantly located within the GaMnAs alloy layers. In the GaMnAs layers, the concentration of V defects ([V]) increases with the concentration of M defects ([M]), consistent with a Fermi-level-dependent vacancy formation energy. Furthermore, [M] is typically two to three times [A] and [V], suggesting significant compensation of the free carriers associated with MnGa. A quantitative defect pair correlation analysis reveals clustering of nearest V–V pairs and anti-clustering of nearest M–M, M–V, and M–A pairs. For all pair separations greater than 2 nm, random distributions of defects are apparent.


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