InAsÕGaAs square nanomesas: Multimillion-atom molecular dynamics simulations on parallel computers

A model potential for GaAs~100! and InAs~100! surface atoms is developed and surface reconstructions on GaAs~100! and InAs~100! are studied with the conjugate gradient ~CG! method. Not only does this model reproduce well surface energies for the ~100! orientation, it also yields (132) dimer lengths in accordance with ab initio calculations. Large-scale molecular dynamics ~MD! simulations are performed to investigate mechanical stresses in InAs/GaAs nanomesas with $101%-type sidewalls. The in-plane lattice constant of InAs layers parallel to the InAs/GaAs~001! interface are found to exceed the InAs bulk value at the twelfth monolayer ~ML! and the hydrostatic stresses in InAs layers become tensile above 12 ML. Hence, it is energetically unfavorable for InAs overlayers to exceed 12 ML. This may explain the experimental finding that the growth of flat InAs overlayers is self-limiting to ;11 ML on GaAs nanomesas. MD simulations are also used to investigate the lateral size effects on the stress distribution and morphology of InAs/GaAs square nanomesas. Two nanomesas with the same vertical size but different lateral sizes are simulated. While a single stress domain is observed in the InAs overlayer of the smaller mesa, two stress domains are found in the larger mesa. This indicates the existence of a critical lateral size for stress domain formation in accordance with recent experimental findings. It is found that the InAs overlayer in the larger mesa is laterally constrained to the GaAs bulk lattice constant at the interface but vertically relaxed to the InAs bulk lattice constant. Surface energies of GaAs and InAs for the ~110! and ~111! orientations are also calculated with the MD and CG methods. © 2003 American Institute of Physics. @DOI: 10.1063/1.1609049#