TITLE:
"Interface Compounds in Heteroepitaxy:  Using Thermodynamics to Control Kinetics"


ABSTRACT:
As microelectronics yields to nanotechnology, interfaces between disparate materials play a dominant role in device fabrication and performance.  Macroscopic properties of these structures are determined in large part by atomic-scale interactions during interface formation.  These interactions are set by thermodynamics, but can be (at least partly) controlled by kinetics.  The important interactions, however, are not bulk properties, but local properties of the surface and forming interface.  This talk will present examples of different phenomena arising during interface formation between silicon and materials with dissimilar atomic size(Ge), valence (GaSe, AlSe), and ionicity (CaF2).   Rarely does one material form neat atomic layers atop another.  Rather, interdiffusion, interface compound formation and/or island growth dominate.  Interfaces can stabilize crystal structures not found in bulk form or force a choice between two bulk structures. Diffusion barriers on interface compounds control the kinetics of the subsequent deposition, leading to different optimal growth parameters for the first and subsequent monolayers.  Passivation of the Si surface with a new interface compound can result in an appropriate substrate for quantum dot formation.  External means to alter the surface energy balance, such as irradiation or surfactant introduction, can change the morphology between laminar and islanded for quantum well and dot technologies, respectively.