Modeling the Growth of Semiconductor Epitaxial Films via Nanosecond Time Scale Molecular Dynamics Simulations

Microscopic and macroscopic growth mechanisms of semiconductor epitaxial films due to Si and Ge deposition on the dimer reconstructed Si{100}-(2 × 1) surface are modeled via molecular dynamics. The forces for solving the classical equations of motion are derived from Tersoff's many-body potential for the multicomponent Si-Ge system. In our model, thermally deposited Si and Ge atoms are allowed to react with the dimer reconstructed Si{100}-(2 × 1) surface for nanosecond durations. For the first time, the microscopic mechanisms of the unreconstruction of the original surface and macroscopic formation of the epilayers of the deposited material are extracted. We find that the dimer openings on the reconstructed surface following the Si or Ge deposition are either due to a diffusing adatom (the deposited atom) induced mechanism or due to a direct insertion of the incoming adatoms into the epitaxial positions. The results reveal a novel mechanism involving cooperative motion of adatoms in which diffusing adatoms move perpendicular to the direction of the dimer rows of the original surface. The resulting relaxation of the underneath substrate and dimer atoms causes the opening of successive dimers along the way. The mechanism is proposed to be responsible for the kinetics of a dramatic enhancement of the crystal growth process in one direction. This prediction has been recently confirmed by using the scanning tunneling microscope (STM). A total of three to six monolayers of epitaxial Si and Ge have been grown in the simulations. Two distinct layer by layer growth modes of macroscopic epitaxial films are observed. In one case the domains of amorphous regions in the growth remain roughly in the same area of the interface throughout the entire thickness. In the other example the reconstructions on the buried interfaces can be relieved by long time equilibrations. The epitaxially deposited films have a tendency to heal the inner layers during nanosecond time scale equilibrations. In accordance with the Rutherford backscattering experiments we also find that the reconstruction remains at the growing interface.