Ab initio Calculation of Structure and Dynamics of Semiconductor Surfaces with Adatoms

Author: Robert Honke
Betreuer: Prof. Dr. U. Schröder
Kolloquium: 2. Juli 1997

Structure and dynamics of adatom induced Si(111)-(1 tex2html_wrap_inline29 1) and Si(111)-( tex2html_wrap_inline31 )R3tex2html_wrap_inline33 surfaces have been studied by means of first principles methods. For the Arsenic and Hydrogen covered 1 tex2html_wrap_inline29 1 surfaces and for the Gallium and Boron covered tex2html_wrap_inline31 surfaces, the relaxation is determined by minimizing the total energy within the local density approximation and the full phonon dispersions are calculated using the density functional perturbation theory (DFPT). The phonons of the Aluminum and Indium covered surfaces are studied within a simple mass approximation. All results for the surface localized modes are in good agreement with the experimental data. The observed anomalously large amplitudes of Ga vibrations at elevated temperatures [1] are compared to the mean square displacements calculated within the harmonic approximation.
Anharmonic effects are scrutinized for the adsorbate vibrations of the Si(111):H-(1 tex2html_wrap_inline29 1) surface. The influence of the zero-point motion and the substrate modes on the Si-H bond stretching mode at the tex2html_wrap_inline43 -point are studied via cubic and quartic anharmonic coupling coefficients which are obtained by combining DFPT and the frozen phonon method. The calculation of the temperature dependent line shift in lowest order perturbation theory includes also the surface thermal expansion. The broadening of the Si-H stretch vibration is obtained within higher order anharmonic perturbation theory using an on-site potential approximation. The results compare well with all available experimental data.

[1] R.E. Martinez, E. Fontes, J.A. Golovchenko, and J.R. Patel, Phys. Rev. Lett. 69, 1061 (1992).