AVS 50th International Symposium
    Semiconductors Thursday Sessions
       Session SC+MI-ThA

Paper SC+MI-ThA6
Cross Sectional Scanning Tunneling Microscopy Studies of Mn Segregation in Ga1-xMnxAs Films

Thursday, November 6, 2003, 3:40 pm, Room 321/322

Session: Ferromagnetic and Dilute Magnetic Semiconductors
Presenter: J.N. Gleason, University of Michigan
Authors: J.N. Gleason, University of Michigan
M.E. Hjelmstad, University of Michigan
R.S. Goldman, University of Michigan
S. Fathpour, University of Michigan
S. Ghosh, University of Michigan
P.K. Bhattacharya, University of Michigan
Correspondent: Click to Email
Ga@sub 1-X@Mn@sub X@As is a promising candidate for spintronic applications compatible with conventional GaAs technologies. Theoretical studies have predicted that an increase in disorder of Mn atom positions will lead to a significant increase in the Curie Temperature.@footnote 1@ Therefore, we have investigated the effects of Mn segregation in Ga@sub 1-X@Mn@sub X@As grown by low temperature molecular beam epitaxy using ultra high vacuum cross-sectional scanning tunneling microscopy (XSTM). The heterostructures consist of 10-period superlattices of alternating Ga@sub 1-X@Mn@sub X@As (x=0.5, 2.5 and 5.0%) and Al@sub 0.20@Ga@sub 0.80@As layers, sandwiched between thick p+ GaAs layers. Constant current XSTM images reveal nanometer-sized regions with higher apparent tip height, presumably related to a local increase in the density of states associated with the presence of Mn atoms in Ga@sub 1-X@Mn@sub X@As. In the x=0.5% films, the nanometer-sized bright regions appear relatively dispersed, with ~ 5nm separation. For the x=2.5% and 5% films, agglomeration of the nanometer-sized bright regions is observed, and apparently increases with increasing Mn composition. The apparent Mn clustering does not appear to be affected by the presence of adjacent Al@sub 0.20@Ga@sub 0.80@As superlattices, indicating that any local misfit stress does not act as a sink for Mn accumulation. The apparent Mn clustering is likely due to a long-range attractive potential between Mn atoms, and may be associated with charge carrier screening, similar to earlier GaAs:Zn studies.@footnote 2@ As the Mn composition increases, the free carrier concentration increases, and the screening length decreases. This would in turn lead to a lower self-repulsion of Mn atoms, and an increase in Mn clustering. We will also discuss the effects of annealing on Mn segregation in Ga@sub 1-X@Mn@sub X@As. @FootnoteText@ @footnote 1@M.Berciu et al., Phys. Rev. Lett. 87, 107203 (2001).@footnote 2@P. Ebert et al., Phys. Rev. Lett. 83, 757 (1999).