arXiv subjects

Caleb Whittier

Publications and source records attributed to Caleb Whittier.

2 recordsLinked to original sources

arXiv2026

Geometric Control of Visible Emitter Creation in Hexagonal Boron Nitride by Oblique Ion Irradiation

Ion irradiation creates optically active defects in wide-bandgap van der Waals materials, yet most approaches tune defect formation by varying the ion species, energy, or fluence while leaving the incidence geometry fixed. The ion-incidence angle is established here as a geometric control parameter for engineering visible emitters in hexagonal boron nitride (hBN). The angle and ion fluence of a plasma-focused heavy-ion (Xe+) beam are varied across hBN flakes of different thickness, and the resulting photoluminescence is quantified. In thick flakes, oblique irradiation shifts the fluence for maximum emission by nearly two orders of magnitude relative to normal incidence, whereas thin flakes exhibit an angle-independent optimum. Ion-trajectory simulations attribute this thickness dependence to lateral redistribution of the collision cascade and enhanced oblique sputtering. Atomic force microscopy identifies distinct processing regimes that delineate the useful defect-creation window. Post-irradiation annealing quenches the emission and shifts the spectral weight toward the green-yellow band while preserving the angle-dependent activation trends. Spectrally resolved lifetime measurements show comparable biexponential dynamics for normal and oblique incidence, consistent with emission from related defect families rather than a geometry-specific emitter species. These results establish ion-incidence geometry as a materials-level knob for programming optical defect activation and spatial defect distributions in van der Waals photonic materials.

physics.optics↗

arXiv2025

Controlled growth of rare-earth-doped TiO$_{2}$ thin films on III-V semiconductors for hybrid quantum photonic interfaces

Quantum photonic networks require two distinct functionalities: bright single-photon sources and long-lived quantum memories. III-V semiconductor quantum dots excel as deterministic and coherent photon emitters, while rare-earth ions such as erbium (Er$^{3+}$) in crystalline oxides offer exceptional spin and optical coherence at telecom wavelengths. Combining these systems and their functionalities via direct epitaxy is challenging due to lattice mismatch and incompatible growth conditions. Here we demonstrate low-temperature pulsed laser deposition of Er$^{3+}$-doped TiO$_{2}$ thin films directly on GaAs and GaSb substrates. Controlled surface preparation with an arsenic cap and an oxygen-deficient buffer layer enables the growth of epitaxial anatase TiO$_{2}$ (001) at 390$^{o}$C with sub-300 pm surface roughness, while avoiding interface degradation. In contrast, high-temperature oxide desorption or growth temperatures drive the transition to rough, polycrystalline rutile film, as confirmed by transmission electron microscopy. Minimal coincident interface area (MCIA) modeling explains the orientation-selective growth on GaAs and GaSb. Raman and cryogenic photoluminescence excitation spectroscopy verify the crystal phase and optical activation of Er$^{3+}$ ions. This multi-parameter growth strategy helps preserve III-V quantum dot functionality and yields smooth surfaces suitable for low-loss nanophotonic structures. Our results establish a materials platform for monolithically integrating rare-earth quantum memories with semiconductor photon sources, paving the way toward scalable hybrid quantum photonic chips.

quant-ph↗