Extent of hydrogen coverage of Si(001) under chemical vapor deposition conditions from ab initio approaches

TL;DR

This study uses advanced ab initio methods to analyze hydrogen coverage on Si(001) surfaces under CVD conditions, predicting temperature-dependent desorption and coverage changes relevant for epitaxy processes.

Contribution

It introduces an interpolated phonon approach for thermodynamic calculations and assesses the accuracy of different computational methods for surface hydrogen coverage.

Findings

Hydrogen desorption begins around 750 K.

Significant coverage changes occur between 1000-1200 K.

Interpolated phonon approach yields accurate thermodynamic predictions.

Abstract

The extent of hydrogen coverage of the Si(001)c(4x2) surface in the presence of hydrogen gas has been studied with dispersion corrected density functional theory. Electronic energy contributions are well described using a hybrid functional. The temperature dependence of the coverage in thermodynamic equilibrium was studied computing the phonon spectrum in a supercell approach. As an approximation to these demanding computations, an interpolated phonon approach was found to give comparable accuracy. The simpler ab initio thermodynamic approach is not accurate enough for the system studied, even if corrections by the Einstein model for surface vibrations are considered. The on-set of H2 desorption from the fully hydrogenated surface is predicted to occur at temperatures around 750 K. Strong changes in hydrogen coverage are found between 1000 and 1200 K in good agreement with previous reflectance anisotropy spectroscopy experiments. These findings allow a rational choice for the surface state in the computational treatment of chemical reactions under typical metal organic vapor phase epitaxy conditions on Si(001).