arXiv subjects

Oana Malis

Publications and source records attributed to Oana Malis.

5 recordsLinked to original sources

arXiv2026

Efficient generation of entangled photons in the telecommunications range using nonlinear metasurfaces integrated with ScAlN/GaN heterostructures

Entangled photons provide non-classical correlations that enable measurement sensitivities beyond classical limits, scalable fault-tolerant quantum computation, and fundamentally secure quantum communication, making them a foundational necessity for next-generation quantum technologies. Here we propose and analyze a novel source of entangled photons based on ScAlN/GaN quantum wells integrated with dielectric metasurfaces. Giant second-order intersubband nonlinearity of the GaN quantum wells with strain-compensated delta-doped ScAlN barriers caused by strong built-in electric fields combined with superior mode-coupling performance of metasurfaces optimized by inverse design give rise to efficient parametric down-conversion and generation of entangled photons in the telecom range. We develop a rigorous Heisenberg-Langevin formalism which includes field quantization, dissipation and fluctuations for all fields, parametric amplification of thermal noise and zero-point fluctuations, and other relevant effects. Our proposed approach of employing the emergent photonic material ScAlN promises high biphoton generation rate over $10^{10}$ s$^{-1}$ from a compact integrated structure that is only 0.5 $μ$m thick while mitigating strain-related issues that have so far impeded progress of nitride-based heterostructures for quantum photonic applications into the infrared and visible wavelengths. Our result therefore is relevant for numerous applications ranging from quantum sensing, quantum information, and computing.

physics.optics↗

arXiv2025

Structural optimization of lattice-matched Sc0.14Al0.86N/GaN superlattices for photonic applications

ScxAl1-xN is an emerging III-nitride material known for its high piezoelectric coefficient and ferroelectric properties. Integration of wide-bandgap ScxAl1-xN with GaN is particularly attractive for quantum photonic devices. Achieving low defect complex multilayers incorporating ScxAl1-xN, though, requires precise lattice-matching and carefully optimized growth parameters. This study systematically investigates the molecular-beam epitaxy of short-period ScxAl1-xN/GaN superlattices with total thicknesses of up to 600 nm on GaN templates. X-ray diffraction reciprocal space mapping confirmed lattice-matching at x = 0.14 Sc composition regardless of the thickness of GaN interlayers, as evidenced by symmetric superlattice satellites aligned in-plane with the underlying substrate peak. Superlattices with Sc compositions deviating from this lattice-matching condition exhibited strain-induced defects ranging from crack formation to partial relaxation. Scanning transmission electron microscopy (STEM) investigation of the ScxAl1-xN/GaN interfaces identified temperature-dependent intermixing as a major factor in setting the nitride composition variation and implicitly band structure profile along the growth direction. Energy-dispersive X-ray spectroscopy also revealed that Sc incorporation exhibits delays relative to Al at both onset and termination. Optimal growth conditions were observed at approximately 600°C and 550°C for superlattices with thick GaN layers (6 nm), and ultra-thin GaN layers (< 2 nm), respectively.

cond-mat.mtrl-sci↗

arXiv2024

Pinpointing Lattice-Matched Conditions for Wurtzite ScxAl1-xN/GaN Heterostructures with X-Ray Reciprocal Space Analysis

Using comprehensive x-ray reciprocal space mapping, we establish the precise lattice-matching composition for wurtzite $Sc_xAl_{1-x}N$ layers on (0001) GaN to be x = 0.14+/-0.01. 100-nm thick $Sc_xAl_{1-x}N$ films (x = 0.09 - 0.19) were grown in small composition increments on c-plane GaN templates by plasma-assisted molecular beam epitaxy. The alloy composition was estimated from the fit of the (0002) x-ray peak positions assuming the c-lattice parameter of ScAlN films coherently-strained on GaN increases linearly with Sc-content determined independently by Rutherford Backscattering Spectrometry. Reciprocal space maps obtained from high-resolution x-ray diffraction measurements of the (10-15) reflection reveal that $Sc_xAl_{1-x}N$ films with x = 0.14+/-0.01 are coherently strained with the GaN substrate while the other compositions show evidence of relaxation. The in-plane lattice-matching with GaN is further confirmed for a 300-nm thick $Sc_{0.14}Al_{0.86}N$ layer. The full-width-at-half-maximum of the (0002) reflection rocking curve for this $Sc_{0.14}Al_{0.86}N$ film is 106 arcseconds and corresponds to the lowest value reported in the literature for wurtzite ScAlN films.

cond-mat.mtrl-sci↗

arXiv2015

Quasi-coherent thermal emitter based on refractory plasmonic materials

The thermal emission of refractory plasmonic metamaterial - a titanium nitride 1D grating - is studied at high operating temperature (540 °C). By choosing a refractory material, we fabricate thermal gratings with high brightness that are emitting mid-infrared radiation centered around 3 $μ$m. We demonstrate experimentally that the thermal excitation of plasmon-polariton on the surface of the grating produces a well-collimated beam with a spatial coherence length of 32λ (angular divergence of 1.8°) which is quasi-monochromatic with a full width at half maximum of 70 nm. These experimental results show good agreement with a numerical model based on a two-dimensional full-wave analysis in frequency domain.

physics.optics↗

arXiv1998

An X-ray Scattering and Simulation Study of the Ordering Kinetics in CuAu

A detailed numerical and experimental study of the ordering of the low temperature tetragonal phase of CuAu is presented. The numerical simulations are based on a coarse-grained free energy derived from electronic structure calculations of CuAu, while the experimental results are obtained from in situ x-ray scattering. Both theoretical and experimental work indicate a subtle kinetic competition between the ordered tetragonal phase and the metastable modulated phase.

cond-mat.stat-mech↗