title: Determining the electronic confinement of a subsurface metallic state.
abstract: Dopant profiles in semiconductors are important for understanding nanoscale electronics. Highly conductive and extremely confined phosphorus doping profiles in silicon, known as Si:P δ-layers, are of particular interest for quantum computer applications, yet a quantitative measure of their electronic profile has been lacking. Using resonantly enhanced photoemission spectroscopy, we reveal the real-space breadth of the Si:P δ-layer occupied states and gain a rare view into the nature of the confined orbitals. We find that the occupied valley-split states of the δ-layer, the so-called 1Γ and 2Γ, are exceptionally confined with an electronic profile of a mere 0.40 to 0.52 nm at full width at half-maximum, a result that is in excellent agreement with density functional theory calculations. Furthermore, the bulk-like Si 3pz orbital from which the occupied states are derived is sufficiently confined to lose most of its pz-like character, explaining the strikingly large valley splitting observed for the 1Γ and 2Γ states.
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU) , N-7491 Trondheim, Norway.
authors.forename: Federico
authors.initials: F
authors.lastname: Mazzola
authors.forename: Mark T
authors.initials: MT
authors.lastname: Edmonds
authors.forename: Kristin
authors.initials: K
authors.lastname: Høydalsvik
authors.forename: Damien John
authors.initials: DJ
authors.lastname: Carter
authors.forename: Nigel A
authors.initials: NA
authors.lastname: Marks
authors.forename: Bruce C C
authors.initials: BC
authors.lastname: Cowie
authors.forename: Lars
authors.initials: L
authors.lastname: Thomsen
authors.forename: Jill
authors.initials: J
authors.lastname: Miwa
authors.forename: Michelle Yvonne
authors.initials: MY
authors.lastname: Simmons
authors.forename: Justin W
authors.initials: JW
authors.lastname: Wells
keywords: 2D confinement; Si:P δ-layers; photoemission; quantum computation