Theoretical studies of strain effects on heteroepitaxial growth of III-V compound semiconductors.

摘要

A comprehensive theoretical analysis based on continuum elasticity theory and atomistic simulations is presented of the interfacial stability with respect to misfit dislocation formation, the strain fields, the film surface morphology, and the kinetics of strain relaxation during layer-by-layer semiconductor heteroepitaxy. In this analysis, the substrate thickness is used as a parameter, thus addressing the effects of using thin compliant substrates in heteroepitaxy. In addition, heteroepitaxial systems that contain one monolayer of In _0.50Ga_0.50As is analyzed to address the simultaneous effects of compositional grading on strain relaxation. The strain in the coherently strained films, the energetics of the transition from a coherent to a semicoherent interface consisting of misfit dislocation arrays or networks, the structure of the corresponding semicoherent interfaces, the strain fields associated with different equilibrium states of strain, and the morphological characteristics of the film surfaces are calculated for InAs/GaAs(110) and InAs/GaAs(111)A. The thickness of the epitaxial film is used as the dynamical variable in the analysis. Critical film thicknesses for; transition from one equilibrium state of strain to another are computed. The effects on the strain relaxation of substrate thickness and of film compositional grading are investigated in the epitaxial growth of InAs on GaAs(111)A. This kinetic analysis is based on a phenomenological mean-field theoretical framework for the dynamics of strain relaxation due to formation of threading dislocations in the film and interfacial misfit dislocations. The results presented here support that the mechanical response of a thin buffer layer is similar to that of a compliant substrate that is unconstrained at its base. The analysis is presented for the more general case of heteroepitaxy on a finite-thickness compliant substrate, while the common case of epitaxy on an infinitely thick substrate is derived as an asymptotic limit of the general case. Continuum elasticity theory is found to describe the atomistic simulation results very well, down to the monolayer-thickness limit.