Stable structure and effects of the substrate Ti pre-treatment on the epitaxial growth of SrTiO3 on GaAs

Abstract

The structural and electronic properties of Ti in the SrTiO3/GaAs(001) interface are studied using the density functional theory. In all the structures examined, the formation energy of Ti on GaAs(001) decreases with decreasing Ti coverage. Sr or Ti adsorption atoms at the fourfold hollow sites with 1/4 monolayer coverage on the GaAs(001) surface are the most energetically favorable. And, Sr atoms are adsorbed on the surface and Ti atoms are adsorbed below the surface, which is in agreement with the results in experiments. Ga vacancy can form spontaneously for the Ga-terminated (001) GaAs surface. Ti atoms may substitute Ga atoms, or accumulate at the voids inside the GaAs film during growth. Not only heterostructures with a regular perovskite but also heterostructures with Ti-insertion and Ti-substitution defects are investigated. The growth of the SrO-layer on the Ga-terminated surface is more stable, although all kinds of sequence among the SrO-, TiO2-layer on a Ga-, As-terminated surface are possible. Substituting Ti for Ga enhances the stability of SrTiO3 on Ga-terminated (001) GaAs. The electronic structures and properties of the heterointerfaces SrTiO3/GaAs(001) are presented, and a metallic behavior is predicted at the interface of SrTiO3/GaAs with/without Ti-insertion.