Thermodynamic stability and growth kinetics of epitaxial SrTiO3on silicon

Abstract

We determine the thermodynamic phase diagram of the epitaxial SrTiO3/Si heterostructure from first principles density functional theory calculations. We demonstrate that the system is not thermodynamically stable with respect to formation of an interfacial SiO2 region under any experimentally attainable oxygen partial pressures. To understand the experimental observation of an atomically abrupt interface without an SiO2 layer, we construct a kinetic model of the growth process. We show that the observed stability of the non-equilibrium interface under both growth and ambient conditions is directly related to the interface chemistry, which gives rise to a large (2.2 eV) barrier for oxygen diffusion to the interface layer and kinetically traps an atomically abrupt interface structure. Our model leads to the prediction of an interface structure in good agreement with experiment, demonstrating that a combination of first-principles computations, thermodynamics, and simple kinetic modeling can be used to determine non-thermodynamic equilibrium atomic structures in complex heterosystems.

Growth and interfacial properties of epitaxial oxides on semiconductors: ab initio insights

“…Applying the same procedure as for SrTiO 3 /Si and enforcing the same constraint of no amorphous SiO 2 formation at the interface, the thermodynamic stability of various BaO/Si interface compositions has been computed [75]. The phase diagram is reproduced in Fig.…”

“…14b) was able to reproduce the main measured XRD peaks, thereby enabling an atomic-scale solution of the interface structure despite the inability of XRD to resolve oxygen atoms. In a later work, comparison of the free energy of the various interfaces coupled with knowledge of the kinetics of oxygen diffusion in the BaO film confirmed that the structure with oxygen at the interface was the one most likely to form during the growth [75]. However, this determination, based on studying a very small portion of the possible structural phase space, would have been completely insufficient to determine the interfacial atomic structure without the complementary and constraining experimental data (and vice versa).…”

“…Over the past decade, a variety of structures for the SrTiO 3 /Si interface have been suggested [57,[66][67][68][75][76][77][78][79]. Many of the proposed structures, a number of which are illustrated in Fig.…”

“…The phase diagram of the SrTiO 3 /Si interface, computed based on DFT [75], is reproduced in Fig. 15.…”

“…A systematic study of 56 distinct interface compositions within a phase space constrained by experimental observations (1 9 1 or 2 9 1 in-plane unit cells) was recently performed [61,75,76]. This set of structures included all the previously published structures mentioned above as well as a number of new ones (e.g., Fig.…”