Local rare-earth dopant structure in a complex-oxide/semiconductor heterojunction: Molecular beam epitaxy grown Yb-doped SrTiO3 on Si(001)

We have investigated the structural and electronic properties of 3 at. % Yb-doped SrTiO3/Si(001) grown by molecular beam epitaxy. Other rare-earth dopants that result in n-type conductivity typically substitute for Sr at the A sites in the ABO3 perovskite lattice. In contrast, Yb is shown to substitute predominantly for Ti at the perovskite B sites based on data from atomically resolved scanning transmission electron microscopy and energy dispersive spectroscopy, as well as extended x-ray absorption fine structure measurements. An atom beam flux (Θ) mismatch was present during film growth because it was assumed that Yb would occupy A sites. As a result of this assumption, the fluxes were set such that ΘYb+ΘSr=ΘTi. The formation of YbTi rather than YbSr results in Sr vacancies and extraneous (i.e., nonlattice) Ti atoms in the films. Yb exhibits two distinct charge states as determined by x-ray absorption spectroscopy and associated theoretical modeling, +2.7 and +2.1. These aliovalent dopants are compensated by donor electrons from oxygen vacancies that form during film growth. The defect complexes resulting from the flux mismatch, together with oxygen vacancies, lead to deep-level electron traps that were detected by resonant photoemission and predicted to be stable by ab initio theory, as well as much higher sheet resistance than that associated with, for instance, La-doped SrTiO3 (STO) films. Ab initio calculations show that the preference for B-site occupancy is driven by low oxygen chemical potential at the growth front as required to deposit STO on Si without SiO2 formation. locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon Physics Subject Headings (PhySH)Density of statesElectrical conductivityElectronic structureFirst-principles calculationsBand structure methodsDensity functional theoryElectron microscopyEmbedded atom modelEnergy-dispersive x-ray spectroscopyHard x-ray photoelectron spectroscopyPhotoemission spectroscopyResistivity measurementsX-ray absorption spectroscopyX-ray diffractionX-ray photoelectron spectroscopy