Surface segregation mechanism during two-dimensional epitaxial growth: The case of dopants in Si and GaAs molecular-beam epitaxy

Abstract
In this paper, we present a physical explanation for the dopant surface segregation during two-dimensional growth in molecular-beam epitaxy. It is shown that the only way to explain dopant behavior is to assume the climbing of dopant atoms over the steps on the surface, during the growth. An energetical analysis of such phenomenon is presented. Taking into account this mechanism during two-dimensional growth, two kinetic equations can be written for each layer. Resolution of the system provides analytical solutions, and the growth rate influence on the doping profile is justified. The applicability of this approach to several dopants both in GaAs and Si is discussed. It appears that the origin of this segregation phenomenon lies in the unfavorable energy situation for the incorporation of a dopant instead of a bulk material atom.