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Instruments / Technical Area	Publication Details	Published	Actions
I09-Surface and Interface Structural Analysis	Local rare-earth dopant structure in a complex-oxide/semiconductor heterojunction: Molecular beam epitaxy grown Yb-doped SrTiO 3 on Si(001) Scott A. Chambers , Enrique Ramerez , Deepa Guragain , Joseph H. Ngai , Peter V. Sushko , Krishna P. Koirala , Yingge Du , Niranjan Govind , Mark E. Bowden , Deepnarayan Biswas , Tien-Lin Lee , Conan Weiland , Joseph C. Woicik Physical Review B 111 DOI: 10.1103/PhysRevB.111.035304 Diamond Proposal Number(s): [25314] Show Abstract ▼ Abstract: 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 𝐴⁢𝐵⁢O3 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.	Jan 2025
I09-Surface and Interface Structural Analysis	Separating electrons and donors in BaSnO3 via band engineering Abhinav Prakash , Nicholas F. Quackenbush , Hwanhui Yun , Jacob T. Held , Tianqi Wang , Tristan Truttmann , James M. Ablett , Conan Weiland , Tien-Lin Lee , Joseph C. Woicik , K. Andre Mkhoyan , Bharat Jalan Nano Letters DOI: 10.1021/acs.nanolett.9b03825 Diamond Proposal Number(s): [15845] Show Abstract ▼ Abstract: Separating electrons from their source atoms in La-doped BaSnO3, the first perovskite oxide semiconductor to be discovered with high room-temperature electron mobility, remains a subject of great interest for achieving high-mobility electron gas in two dimensions. So far, the vast majority of work in perovskite oxides has focused on heterostructures involving SrTiO3 as an active layer. Here we report the demonstration of modulation doping in BaSnO3 as high room temperature mobility host without the use of SrTiO3. Significantly, we show the use of angle- resolved hard X-ray photoelectron spectroscopy (HAXPES) as a non-destructive approach to not only determine the location of electrons at the buried interface but also to quantify the width of electron distribution in BaSnO3. The transport results are in good agreement with the results of self-consistent solution to one-dimensional Poisson and Schrödinger equations. Finally, we discuss viable routes to engineer two-dimensional electron gas density through band-offset engineering.	Nov 2019

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