AVS 50th International Symposium
    Semiconductors Friday Sessions
       Session SC+NS-FrM

Paper SC+NS-FrM3
Self-Assembly of Nanostructures in GaAs/InAs and GaAs/GaSb Multilayer Structures

Friday, November 7, 2003, 9:00 am, Room 321/322

Session: Low Dimensional Structures and Amorphous Silicon
Presenter: C.A. Pearson, University of Michigan, Flint
Authors: C.A. Pearson, University of Michigan, Flint
C. Dorin, University of Michigan, Flint
J. Mirecki Millunchick, University of Michigan, Flint
Y. Chen, University of Michigan, Flint
B.G. Orr, University of Michigan, Flint
Correspondent: Click to Email
Reproducibly obtaining regular arrays of phase-separated material is a promising way to acquire low dimensional structures such as quantum dots or wires. Short period superlattice (SPS) structures, where each layer is approximately one or two monolayers thick, can spontaneously phase separate under certain growth conditions resulting in compositional modulations. The appearance of lateral composition modulation is correlated to roughening of the surface front. To further elucidate this progression, in situ scanning tunneling microscopy (STM) was used to examine SPS structures at integral and fractional periods, where one period consists of 2 monolayers (ML) of GaAs followed by 2 ML of InAs or GaSb. For both integral and fractional periods, the surfaces are quite distinct. The as-grown InAs surface is decorated with anisotropic islands that exhibit a (2x4) reconstruction upon a terrace with a (nx3) reconstruction. The GaAs terminated surfaces are characterized by flat mesa structures surrounded by deep trenches. With increasing number of periods, both surfaces evolved towards greater long scale roughness. Furthermore, the islands (InAs terminated) or trenches (GaAs terminated) become larger and show a preferential lateral arrangement with a characteristic separation in the [110] direction of ~20 nm, which corresponds to the modulation wavelength observed using other techniques. Similar results are also observed in the GaAs/GaSb structure where islanding of GaAs is observed in a GaSb matrix. These results are consistent with continuum perturbation models that predict the coupling of morphological and compositional instabilities under the appropriate circumstances.