Joanna Millunchick

Self-Assembly of Compound Semiconductor Nanostructures: Nucleation and Growth of GaSb/GaAs(001) Quantum Dots

Sponsor: Department of Energy
Quantum Dots (QDs) are of technological importance for numerous possible applications in optoelectronic devices. Current most QDs are made out of InAs, however GaSb could be a potential alternative for QD formation due to its similar lattice parameter. We are studying the nucleation and growth of GaSb in a mixed anion system. Typically when GaSb is grown on GaAs(001) QDs with an elongation in the [110] result due to the surface anisotropy of the dimer rows which make the [110] directions the fastest diffusion directions. Recent experiments have shown that it is possible to grow GaSb QDs which are bounded by [100] facets. This is interesting because the [100] direction is the elastically soft direction. The GaSb/GaAs system is known to contain 90° misfit dislocations and 60° threading dislocations. These facets could be due to the formation of misfit dislocations early in the growth stages of the quantum dots. Ultimately we hope to use our knowledge of the orientation combined with patterning using an in situ Focused Ion Beam to produce well controlled QDs of GaSb on GaAs.
Highlights (Click an image for more information)
  • STM image of 1ML of GaSb/GaAs(001)

    1ML GaSb wetting layer on GaAs(100) shows a mixed α2 and β2 (4x3) reconstruction with deep trenches to relieve strain. On top of this monolayer small islands and wires form nucleation spots for QDs.

  • Dual Bias Pair of Sb/GaAs(001)

    Dual Bias images of 0.8ML Sb/GaAs(001) at +/-3V suggest that the mixed (2x4)-(4x3) surface consists of a combination of alpha and beta2(2x4) with an alpha(4x3). The (2x4)s both have surface anion dimers with the alpha(4x3) consists of surface hertodimers which is why it is bright under both bias voltages.