Morphologies of diamond films from atomic-scale simulations of chemical vapor deposition

The growth of {110}- and {111}-oriented diamond films under typical chemical vapor deposition (CVD) conditions was simulated on the atomic scale. The films are represented in three dimensions by diamond cubic crystal lattices, and thus the effects of surface atomic structure and film morphology are built into the model. The temporal evolution of the films during growth is accomplished by a kinetic Monte Carlo scheme parameterized by conventional surface chemical reaction-rate coefficients. Growth on {110}:H and {111}:H surfaces was simulated in atmospheres containing H, H₂, CH₃ and various partial pressures of C₂H₂. Film growth rates and morphologies are found to depend strongly on the presence of C₂H₂ at the surface. Under typical growth conditions, film growth rates agree well with experiment and other modeling studies, and the film morphologies are atomically rough. However, growth of {110} and {111} films in C₂H₂-deficient environments is found to be controlled by the nucleation of diamond clusters on smooth faces, and growth rates are very low under these conditions. This is because the initiation of a monolayer on smooth {110} and {111} facets requires the bonding of two and three adsorbed C atoms, respectively. Since a single C₂H₂ molecule contributes two C atoms when it is chemisorbed, the presence of C₂H₂ is important to {110} and especially {111} growth. The {111} films grow by the flow of atomic-height steps at triangular islands on the surface and are atomically smooth when the partial pressure of C₂H₂ is very low. The {110} films grow by one-dimensional step flow in the atomic "troughs" of the {110}-terminated diamond cubic surface, and become corrugated into {111} microfacets.