Epitaxial Cr on n-SrTiO3(001)—An ideal Ohmic contact

Abstract

The influence of the top-contact metal on the ferroelectric properties of epitaxial ferroelectric Pb ( Zr 0.2 Ti 0.8 ) O 3 thin films

Ultralow Contact Resistance at an Epitaxial Metal/Oxide Heterojunction Through Interstitial Site Doping

“…This feature exhibits momentum dispersions similar to those of the O 2 p ‐derived valence band, consistent with Cr 3 d –O 2 p hybridization, as seen in the Supporting Information. Finally, the absolute Ti 2p 3/2 binding energy after 0.9 ML Cr deposition (459.33 eV) reveals that the Fermi level is ∼0.2 eV below the conduction band minimum, as also observed for Cr depositions of 1 to 3 u.c 20. Thus, metallization of the STO surface results from as little as ∼1 ML Cr.…”

“…Au neither grows epitaxially14 nor makes an Ohmic contact to STO(001), but rather forms a Schottky barrier 2, 15–17. In contrast, Cr has been shown to nucleate as oriented islands18, 19 which coalesce into monolithic epitaxial films and form an ideal Ohmic contact to STO(001) 20. The resistivity is very low, 29 mΩ ‐ cm, comparable to that measured for soldered In contacts onto STO at the same Nb doping level as is used here 9.…”

“…Body‐centered cubic Cr(001) nucleates epitaxially on STO(001) and is accompanied by a 45° rotation about [001] such that [110] Cr ‖ [100] STO when grown at a substrate temperature between ∼100 °C and ∼600 °C 12, 18–22. One misfit dislocation is expected every 11.9 unit cells (u.c.)…”

Stability at the surface

“…This electrical junction should be rectifying. However, even though the two lattices line up as expected, the junction is perfectly ohmic, and the contact resistance is as low as any measured for any metal on SrTiO 3 ( 2). The reason for this completely unexpected electrical behavior is an unanticipated interface structure in which a fraction of the first atomic layer of Cr atoms diffuses into the SrTiO 3 , occupies interstitial sites in the lattice, transfers charge to the adjacent Ti ions, and metallizes the interface ( 3).…”

Dominance of Interface Chemistry over the Bulk Properties in Determining the Electronic Structure of Epitaxial Metal/Perovskite Oxide Heterojunctions

“…It grows epitaxially on STO(001), despite a +4.3% in-plane lattice mismatch, and forms a nearly perfect ohmic contact with a contact resistivity of 29 mΩ·cm. 6 The reason for this unexpected, but very useful behavior is that during initial nucleation, some Cr atoms diffuse into the STO and occupy interstitial sites within the first few atomic planes. 7 This diffusion process results in two highly desirable features.…”