title: Interfacial Engineering of Semiconductor-Superconductor Junctions for High Performance Micro-Coolers.
abstract: The control of electronic and thermal transport through material interfaces is crucial for numerous micro and nanoelectronics applications and quantum devices. Here we report on the engineering of the electro-thermal properties of semiconductor-superconductor (Sm-S) electronic cooler junctions by a nanoscale insulating tunnel barrier introduced between the Sm and S electrodes. Unexpectedly, such an interface barrier does not increase the junction resistance but strongly reduces the detrimental sub-gap leakage current. These features are key to achieving high cooling power tunnel junction refrigerators, and we demonstrate unparalleled performance in silicon-based Sm-S electron cooler devices with orders of magnitudes improvement in the cooling power in comparison to previous works. By adapting the junctions in strain-engineered silicon coolers we also demonstrate efficient electron temperature reduction from 300 mK to below 100 mK. Investigations on junctions with different interface quality indicate that the previously unexplained sub-gap leakage current is strongly influenced by the Sm-S interface states. These states often dictate the junction electrical resistance through the well-known Fermi level pinning effect and, therefore, superconductivity could be generally used to probe and optimize metal-semiconductor contact behaviour.
authors.affiliation: VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT Espoo, Finland.
authors.forename: D
authors.initials: D
authors.lastname: Gunnarsson
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: J S
authors.initials: JS
authors.lastname: Richardson-Bullock
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Prest
authors.affiliation: Low Temperature Laboratory (OVLL), Aalto University School of Science, PO Box 13500, FI-00076 Aalto, Finland.
authors.forename: H Q
authors.initials: HQ
authors.lastname: Nguyen
authors.affiliation: VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT Espoo, Finland.
authors.forename: A V
authors.initials: AV
authors.lastname: Timofeev
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: V A
authors.initials: VA
authors.lastname: Shah
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: T E
authors.initials: TE
authors.lastname: Whall
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: E H C
authors.initials: EHC
authors.lastname: Parker
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: D R
authors.initials: DR
authors.lastname: Leadley
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: M
authors.initials: M
authors.lastname: Myronov
authors.affiliation: VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT Espoo, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Prunnila