arXiv subjects

Quinn T. Campbell

Publications and source records attributed to Quinn T. Campbell.

10 recordsLinked to original sources

arXiv2026

Epitaxial Displacement-etched GaAsSb Quantum Dots Emitting at Telecom Wavelengths

Semiconductor quantum dots (QDs) are essential components for integrated photonic and quantum information systems, yet current epitaxial growth techniques face significant limitations in complexity of growth, material selection, and density tunability. Here we report a displacement etch technique that enables controlled formation of GaAsSb QDs with emission at telecommunications wavelengths. Our approach uses arsenic molecular flux (As$_2$) to react with antimonide surfaces through thermodynamically favorable displacement reactions, creating three-dimensional quantum confined nanostructures without requiring strain-driven growth or complex droplet-based processes. Density functional theory shows the two competing As-for-Sb exchange pathways to be nearly equivalent in both reaction energy and activation barrier, which places morphological control in the subsequent adatom kinetics rather than in the surface reaction itself. A single process parameter, the As$_2$ exposure, sets the QD areal density across three orders of magnitude, from 10$^2$ to 10$^5$ $μm^{-2}$, covering both isolated emitters and dense gain media. Structural analysis reveals well-defined GaAsSb QDs with a mixed GaAs/GaSb composition and no extended defects. Temperature-dependent photoluminescence measurements confirm emission at 1550 nm (0.8 eV) within the telecommunications C-band, with characteristic QD-like temperature dependence. Because the QDs form on a lattice-matched GaSb surface in a single growth step, the technique offers a practical route to C-band emitters built into the GaSb/AlGaSb device family already used for mid-infrared sources and detectors.

cond-mat.mtrl-sci↗

arXiv2026

Island Sliding Barriers: A first-principles metric for determining remote epitaxy viability

Remote epitaxy, where a 2D van der Waals material (usually graphene) is inserted on top of the substrate before film epitaxy, has emerged as a promising path for growing electronics with lower defect rates and less stringent lattice matching requirements. The exact mechanism behind remote epitaxy has not been definitively shown, however, and it is not obvious when examining a new substrate-film pair whether they would be compatible with the remote epitaxy process. In this paper, we use first principles calculations to test several different mechanisms for determining whether a given substrate-film pair will successfully be grown with remote epitaxy. We find that previously calculated metrics such as electrostatic potential do not hold sufficient explanatory power. We find that the sliding barrier of small islands on the surface when the atomic positions are allowed to optimize provides the most rigorous criteria for whether a given substrate-film pair is remote epitaxy active. This indicates that remote epitaxy is likely a phenomenon related to the kinetics and ease of island migration on the graphene surface.

cond-mat.mtrl-sci↗

arXiv2026

First principles band structure of interacting phosphorus and boron/aluminum $δ$-doped layers in silicon

Silicon can be heavily doped with phosphorus in a single atomic layer (a $δ$ layer), significantly altering the electronic structure of the conduction bands within the material. Recent progress has also made it possible to further dope silicon with acceptor-based $δ$ layers using either boron or aluminum, making it feasible to create devices with interacting $δ$ layers with opposite polarity. Using Density Functional Theory, we calculate the electronic structure of a phosphorus-based $δ$ layer interacting with a boron or aluminum $δ$ layer, varying the distances between the $δ$ layers. At separations 1 nm and smaller, the dopant potentials overlap and largely cancel each other out, leading to an electronic structure closely mimicking intrinsic silicon. At separations greater than 1 nm, the two $δ$ layers behave independently of one another, with an equivalent electronic structure to a p-n diode with an intrinsic layer taking the place of the depletion region. One mechanism for charge transfer between $δ$ layers at larger distances could be tunneling, where we see a tunneling probability exceeding what would be seen for a standard silicon 1.1 eV triangular barrier, indicating that the interaction between delta layers may enhance tunneling compared to a traditional junction.

cond-mat.mtrl-sci↗

arXiv2025

Optimizing Temperature Distributions for Training Neural Quantum States using Parallel Tempering

Parameterized artificial neural networks (ANNs) can be very expressive ansatzes for variational algorithms, reaching state-of-the-art energies on many quantum many-body Hamiltonians. Nevertheless, the training of the ANN can be slow and stymied by the presence of local minima in the parameter landscape. One approach to mitigate this issue is to use parallel tempering methods, and in this work we focus on the role played by the temperature distribution of the parallel tempering replicas. Using an adaptive method that adjusts the temperatures in order to equate the exchange probability between neighboring replicas, we show that this temperature optimization can significantly increase the success rate of the variational algorithm with negligible computational cost by eliminating bottlenecks in the replicas' random walk. We demonstrate this using two different neural networks, a restricted Boltzmann machine and a feedforward network, which we use to study a toy problem based on a permutation invariant Hamiltonian with a pernicious local minimum and the J1-J2 model on a rectangular lattice.

quant-ph↗

arXiv2025

First-principles dissociation pathways of BCl$_3$ on the Si(100)-2$\times$1 surface

One of the most promising acceptor precursors for atomic-precision $δ$-doping of silicon is BCl$_3$. The chemical pathway, and the resulting kinetics, through which BCl$_3$ adsorbs and dissociates on silicon, however, has only been partially explained. In this work, we use density functional theory to expand the dissociation reactions of BCl$_3$ to include reactions that take place across multiple silicon dimer rows, and reactions which end in a bare B atom either at the surface, substituted for a surface silicon, or in a subsurface position. We further simulate resulting scanning tunneling microscopy images for each of these BCl$_x$ dissociation fragments, demonstrating that they often display distinct features that may allow for relatively confident experimental identification. Finally, we input the full dissociation pathway for BCl$_3$ into a kinetic Monte Carlo model, which simulates realistic reaction pathways as a function of environmental conditions such as pressure and temperature of dosing. We find that BCl$_2$ is broadly dominant at low temperatures, while high temperatures and ample space on the silicon surface for dissociation encourage the formation of bridging BCl fragments and B substitutions on the surface. This work provides the chemical mechanisms for understanding atomic-precision doping of Si with B, enabling a number of relevant quantum applications such as bipolar nanoelectronics, acceptor-based qubits, and superconducting Si.

cond-mat.mtrl-sci↗

arXiv2024

Direct measurement of 2DEG states in shallow Si:Sb $δ$-layers

We investigate the electronic structure of high-density layers of Sb dopants in a silicon host, so-called Si:Sb $δ$-layers. We show that, in spite of the known challenges in producing highly confined Sb $δ$-layers, sufficient confinement is created such that the lowest conduction band states ($Γ$ states, studied in depth in other silicon $δ$-layers), become occupied and can be observed using angle-resolved photoemission spectroscopy. The electronic structure of the Si:Sb $δ$-layers closely resembles that of Si:P systems, where the observed conduction band is near-parabolic and slightly anisotropic in the $\mathbf{k}_\parallel$ plane. The observed $Γ$ state extends ~ 1 nm in the out-of-plane direction, which is slightly wider than the 1/3 monolayer thick dopant distribution. This is caused by a small segregation of the dopant layer, which is nevertheless minimal when comparing with earlier published attempts. Our results serve to demonstrate that Sb is still a feasible dopant alternative for use in the semiconductor $δ$-layer platform, providing similar electronic functionality to Si:P systems. Additionally, it has the advantages of being less expensive, more controllable, safer to handle, and more compatible with industrial patterning techniques. Si:Sb is therefore a viable platform for emerging quantum device applications.

cond-mat.mtrl-sci↗

arXiv2024

Voltage dependent first-principles barriers to Li transport within Li ion battery Solid Electrolyte Interphases

Charging a Li ion battery requires Li ion transport between the cathode and the anode. This Li ion transport is dependent upon (among other factors) the electrostatic environment the ion encounters within the Solid Electrolyte Interphase (SEI), which separates the anode from the surrounding electrolyte. Previous first principles work has illuminated the reaction barriers through likely atomistic SEI environments, but has had difficulty accurately reflecting the larger electrostatic potential landscape that an ion encounters moving through the SEI. In this work, we apply the recently developed Quantum Continuum Approximation (QCA) technique to provide an equilibrium electronic potentiostat for first-principles interface calculations. Using QCA, we calculate the potential barrier for Li ion transport through LiF, Li$_2$O, and Li$_2$CO$_3$ SEIs along with LiF-LiF, and LiF-Li$_2$O grain boundaries, all paired with Li metal anodes. We demonstrate that the SEI potential barrier is dependent on the anode electrochemical potentials in each system. Finally, we use these techniques to estimate the change in the diffusion barrier for a Li ion moving in a LiF SEI as a function of anode potential. We find that properly accounting for interface and electronic voltage effects significantly lowers reaction barriers compared to previous literature results.

cond-mat.mtrl-sci↗

arXiv2023

Electronic structure of boron and aluminum $δ$-doped layers in silicon

Recent work on atomic-precision dopant incorporation technologies has led to the creation of both boron and aluminum $δ$-doped layers in silicon with densities above the solid solubility limit. We use density functional theory to predict the band structure and effective mass values of such $δ$ layers, first modeling them as ordered supercells. Structural relaxation is found to have a significant impact on the impurity band energies and effective masses of the boron layers, but not the aluminum layers. However, disorder in the $δ$ layers is found to lead to significant flattening of the bands in both cases. We calculate the local density of states and doping potential for these $δ$-doped layers, demonstrating that their influence is highly localized with spatial extents at most 4 nm. We conclude that acceptor $δ$-doped layers exhibit different electronic structure features dependent on both the dopant atom and spatial ordering. This suggests prospects for controlling the electronic properties of these layers if the local details of the incorporation chemistry can be fine tuned.

cond-mat.mtrl-sci↗

arXiv2021

Optimizing accuracy and efficacy in data-driven materials discovery for the solar production of hydrogen

The production of hydrogen fuels, via water splitting, is of practical relevance for meeting global energy needs and mitigating the environmental consequences of fossil-fuel-based transportation. Water photoelectrolysis has been proposed as a viable approach for generating hydrogen, provided that stable and inexpensive photocatalysts with conversion efficiencies over 10% can be discovered, synthesized at scale, and successfully deployed (Pinaud et al., Energy Environ. Sci., 2013, 6, 1983). While a number of first-principles studies have focused on the data-driven discovery of photocatalysts, in the absence of systematic experimental validation, the success rate of these predictions may be limited. We address this problem by developing a screening procedure with co-validation between experiment and theory to expedite the synthesis, characterization, and testing of the computationally predicted, most desirable materials. Starting with 70,150 compounds in the Materials Project database, the proposed protocol yielded 71 candidate photocatalysts, 11 of which were synthesized as single-phase materials. Experiments confirmed hydrogen generation and favorable band alignment for 6 of the 11 compounds, with the most promising ones belonging to the families of alkali and alkaline-earth indates and orthoplumbates. This study shows the accuracy of a nonempirical, Hubbard-corrected density-functional theory method to predict band gaps and band offsets at a fraction of the computational cost of hybrid functionals, and outlines an effective strategy to identify photocatalysts for solar hydrogen generation.

cond-mat.mtrl-sci↗

arXiv2020

Photo-physics and electronic structure of lateral graphene/MoS2 and metal/MoS2 junctions

Integration of semiconducting transition metal dichalcogenides (TMDs) into functional optoelectronic circuitries requires an understanding of the charge transfer across the interface between the TMD and the contacting material. Here, we use spatially resolved photocurrent microscopy to demonstrate electronic uniformity at the epitaxial graphene/molybdenum disulfide (EG/MoS2) interface. A 10x larger photocurrent is extracted at the EG/MoS2 interface when compared to metal (Ti/Au) /MoS2 interface. This is supported by semi-local density-functional theory (DFT), which predicts the Schottky barrier at the EG/MoS2 interface to be ~2x lower than Ti/MoS2. We provide a direct visualization of a 2D material Schottky barrier through combination of angle resolved photoemission spectroscopy with spatial resolution selected to be ~300 nm (nano-ARPES) and DFT calculations. A bending of ~500 meV over a length scale of ~2-3 micrometer in the valence band maximum of MoS2 is observed via nano-ARPES. We explicate a correlation between experimental demonstration and theoretical predictions of barriers at graphene/TMD interfaces. Spatially resolved photocurrent mapping allows for directly visualizing the uniformity of built-in electric fields at heterostructure interfaces, providing a guide for microscopic engineering of charge transport across heterointerfaces. This simple probe-based technique also speaks directly to the 2D synthesis community to elucidate electronic uniformity at domain boundaries alongside morphological uniformity over large areas.

physics.app-ph↗