Joanna Millunchick

Thermodynamic Phase Stability and Disorder of Surface Structure in Compound Semiconductor Alloys

Collaborators: Prof. Anton van der Ven, University of Michigan-Ann Arbor; Dr. Normand Modine, Sandia National Laboratory
Sponsor: Department of Energy
The nanoscale surface structure of epitaxially grown III-V semiconductor alloys plays a significant role in interfacial properties and self assembly for optoelectronic devices. In order to determine the principles which give rise to various structures and how to direct their formation in synthesis, we are taking an approach which couples computation and experiment to study phase stability, two-phase coexistence, and disorder of III-V surface reconstructions. Monte Carlo simulation employing density functional theory (DFT) energy calculations is used to predict finite-temperature entropic effects on surface structure and composition of the InxGa1-xAs model system. These results are compared to experimental data from films grown via molecular beam epitaxy (MBE) and characterized in situ via STM.
Highlights (Click an image for more information)
  • Monte Carlo Free Energy of InGaAs 2x4 Reconstruction

    Phase stability plot of α2(2x4) (red) and β2(2x4) (black) reconstructions, as determined by density functional theory calculations. The green line shows the free energy at finite temperature, as predicted by Monte Carlo. The drop in energy is due to the high configurational entropy of the α2(2x4) relative to the β2(2x4)