Abstract:Scanning tunneling microscopy (STM) enables the fabrication of two-dimensional δ-doped structures in Si with atomistic precision, with applications from tunnel field-effect transistors to qubits. The combination of a very small contact area and the restrictive thermal budget necessary to maintain the integrity of the δ layer make developing a robust electrical contact method a significant challenge to realizing the potential of atomically precise devices. We demonstrate a method for electrical contact using Pd… Show more
“…The device is then epitaxially encapsulated with intrinsic Si by using an optimized locking-layer process to suppress dopant movement at the atomic scale during epitaxial overgrowth 12,14 . The sample is then removed from the UHV system and Ohmic-contacted with e-beam-defined palladium silicide contacts 15 .…”
Section: Discussionmentioning
confidence: 99%
“…In this study, we overcome previous challenges by uniquely combining hydrogen lithography that generates atomically abrupt device patterns 10,11 with recent progress in low-temperature epitaxial overgrowth using a locking-layer technique [12][13][14] and silicide electrical contact formation 15 to substantially reduce unintentional dopant movement. These advances have allowed us to demonstrate the exponential scaling of the tunneling resistance on the tunnel gap separation in a systematic and reproducible manner.…”
mentioning
confidence: 99%
“…We suppress unintentional dopant movement at the atomic scale using an optimized, room temperature grown locking layer, which not only locks the dopant position within lithographically defined regions during encapsulation, but also improves reproducibility since the critical first few layers are always grown at room temperature 12 . Furthermore, our recent development of a high-yield, low-temperature method for forming ohmic contact to burried atomic devices enables robust electrical characteriation of STM-patterned devices with minimum thermal impact on dopant confinement 15 . With improved capabilities to define and maintain atomically abrupt dopant confinement in silicon, we fabricated a series of STM-patterned Si:P SETs, where we systematically vary the tunnel junction gap separation, and have used them to demonstrate and explore atomic-scale control of the tunnel coupling.…”
Atomically precise donor-based quantum devices are a promising candidate for solid-state quantum computing and analog quantum simulations. However, critical challenges in atomically precise fabrication have meant systematic, atomic scale control of the tunneling rates and tunnel coupling has not been demonstrated. Here using a room temperature grown locking layer and precise control over the entire fabrication process, we reduce unintentional dopant movement while achieving high quality epitaxy in scanning tunnelling microscope (STM)-patterned devices. Using the Si(100)2 × 1 surface reconstruction as an atomically-precise ruler to characterize the tunnel gap in precision-patterned single electron transistors, we demonstrate the exponential scaling of the tunneling resistance on the tunnel gap as it is varied from 7 dimer rows to 16 dimer rows. We demonstrate the capability to reproducibly pattern devices with atomic precision and a donor-based fabrication process where atomic scale changes in the patterned tunnel gap result in the expected changes in the tunneling rates.
“…The device is then epitaxially encapsulated with intrinsic Si by using an optimized locking-layer process to suppress dopant movement at the atomic scale during epitaxial overgrowth 12,14 . The sample is then removed from the UHV system and Ohmic-contacted with e-beam-defined palladium silicide contacts 15 .…”
Section: Discussionmentioning
confidence: 99%
“…In this study, we overcome previous challenges by uniquely combining hydrogen lithography that generates atomically abrupt device patterns 10,11 with recent progress in low-temperature epitaxial overgrowth using a locking-layer technique [12][13][14] and silicide electrical contact formation 15 to substantially reduce unintentional dopant movement. These advances have allowed us to demonstrate the exponential scaling of the tunneling resistance on the tunnel gap separation in a systematic and reproducible manner.…”
mentioning
confidence: 99%
“…We suppress unintentional dopant movement at the atomic scale using an optimized, room temperature grown locking layer, which not only locks the dopant position within lithographically defined regions during encapsulation, but also improves reproducibility since the critical first few layers are always grown at room temperature 12 . Furthermore, our recent development of a high-yield, low-temperature method for forming ohmic contact to burried atomic devices enables robust electrical characteriation of STM-patterned devices with minimum thermal impact on dopant confinement 15 . With improved capabilities to define and maintain atomically abrupt dopant confinement in silicon, we fabricated a series of STM-patterned Si:P SETs, where we systematically vary the tunnel junction gap separation, and have used them to demonstrate and explore atomic-scale control of the tunnel coupling.…”
Atomically precise donor-based quantum devices are a promising candidate for solid-state quantum computing and analog quantum simulations. However, critical challenges in atomically precise fabrication have meant systematic, atomic scale control of the tunneling rates and tunnel coupling has not been demonstrated. Here using a room temperature grown locking layer and precise control over the entire fabrication process, we reduce unintentional dopant movement while achieving high quality epitaxy in scanning tunnelling microscope (STM)-patterned devices. Using the Si(100)2 × 1 surface reconstruction as an atomically-precise ruler to characterize the tunnel gap in precision-patterned single electron transistors, we demonstrate the exponential scaling of the tunneling resistance on the tunnel gap as it is varied from 7 dimer rows to 16 dimer rows. We demonstrate the capability to reproducibly pattern devices with atomic precision and a donor-based fabrication process where atomic scale changes in the patterned tunnel gap result in the expected changes in the tunneling rates.
“…We use a room-temperature grown locking layer technique to suppress atomic-scale movement of the precisely defined dopant atom positions 26 before a subsequent low-temperature (~250 °C) epitaxial Si overgrowth, that embeds the dopant atoms in a 3-dimensional crystalline Si environment. Finally, ohmic contacts to the buried electrodes are formed using a low thermal budget silicide contacting technique 27 . Fig.…”
The Hubbard model is an essential tool for understanding many-body physics in condensed matter systems. Artificial lattices of dopants in silicon are a promising method for the analog quantum simulation of extended Fermi-Hubbard Hamiltonians in the strong interaction regime. However, complex atom-based device fabrication requirements have meant emulating a tunable two-dimensional Fermi-Hubbard Hamiltonian in silicon has not been achieved. Here, we fabricate 3 × 3 arrays of single/few-dopant quantum dots with finite disorder and demonstrate tuning of the electron ensemble using gates and probe the many-body states using quantum transport measurements. By controlling the lattice constants, we tune the hopping amplitude and long-range interactions and observe the finite-size analogue of a transition from metallic to Mott insulating behavior. We simulate thermally activated hopping and Hubbard band formation using increased temperatures. As atomically precise fabrication continues to improve, these results enable a new class of engineered artificial lattices to simulate interactive fermionic models.
“…These values are slightly lower than sheet resistance values reported for B δ-doped nanowires fabricated from B 2 H 6 9 and slightly higher compared to P δ-doped nanowires fabricated from PH 3 . 32,52 The higher sheet resistance of W2 is possibly due to the higher temperature anneal of the locking layer (400 °C) compared to that of W1 (350 °C). This would follow the trend observed with samples B2 and B3 with the higher temperature dose of B3 compared to B2 leading to a higher sheet resistance.…”
Atomically precise, δ-doped structures forming electronic devices in Si have been routinely fabricated in recent years by using depassivation lithography in a scanning tunneling microscope (STM). While H-based precursor/monatomic resist chemistries for incorporation of donor atoms have dominated these efforts, the use of halogen-based chemistries offers a promising path toward atomic-scale manufacturing of acceptor-based devices. Here, B-doped δ-layers were fabricated in Si(100) by using BCl 3 as an acceptor dopant precursor in ultrahigh vacuum. Additionally, we demonstrate compatibility of BCl 3 with both H and Cl monatomic resists to achieve area-selective deposition on Si. In comparison to bare Si, BCl 3 adsorption selectivity ratios for H-and Cl-passivated Si were determined by secondary ion mass spectrometry depth profiling (SIMS) to be 310(10):1 and 1529(5):1, respectively. STM imaging revealed that BCl 3 adsorbed readily on bare Si at room temperature, with SIMS measurements indicating a peak B concentration greater than 1.2(1) × 10 21 cm −3 with a total areal dose of 1.85(1) × 10 14 cm −2 resulting from a 30 langmuir BCl 3 dose at 150 °C. In addition, SIMS showed a δ-layer thickness of ∼0.5 nm. Hall bar measurements of a similar sample were performed at 3.0 K, revealing a sheet resistance of ρ □ = 1.9099(4) kΩ □ −1 , a hole carrier concentration of p = 1.90(2) × 10 14 cm −2 , and a hole mobility of μ = 38.0(4) cm 2 V −1 s −1 without performing an incorporation anneal. Finally, 15 nm wide B δ-doped nanowires were fabricated from BCl 3 and were found to exhibit ohmic conduction. This validates the use of BCl 3 as a dopant precursor for atomicprecision fabrication of acceptor-doped devices in Si and enables development of simultaneous n-and p-type doped bipolar devices.
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