arXiv subjects

Aris Koulas-Simos

Publications and source records attributed to Aris Koulas-Simos.

13 recordsLinked to original sources

arXiv2026

An integrated all-van der Waals nanobeam laser

Transition-metal dichalcogenides offer a promising platform for integrated coherent light sources, yet lasing has largely relied on hybrid photonic architectures without direct quantum-optical verification. Here, we demonstrate an all-van der Waals (all-vdW) high-$β$ nanobeam laser based on a WS$_2$/MoSe$_2$/WS$_{2}$ heterostructure, with the MoSe$_2$ monolayer directly integrated in the WS$_{2}$-based optical resonator for optimal gain-mode overlap. The devices exhibit efficient exciton-cavity coupling at cryogenic temperatures, strongly directional and linearly polarized emission, soft nonlinear input-output characteristics and linewidth narrowing, enabling lasing operation with $β$ near unity. Excitation-power-dependent photon-autocorrelation measurements reveal a transition from thermal to Poissonian photon statistics, with $g_{\mathrm{peak}}^{(2)}(0)$ decreasing from $(1.28\,\pm\,0.09)$ near threshold to $(1.07\,\pm\,0.07)$ above threshold, directly verifying lasing operation. Furthermore, temporal broadening of the autocorrelation uncovers fluctuation-dominated lasing dynamics. These results establish all-vdW heterostructures as a highly attractive platform for integrated coherent light sources in layered-material photonic architectures and scalable quantum-photonic circuits.

physics.optics↗

arXiv2026

Energy-time entanglement from a monolithically integrated quantum dot on silicon

Scalable quantum photonic technologies require deterministic sources of entangled photons that are compatible with established semiconductor manufacturing platforms. While self-assembled III--V semiconductor quantum dots are among the most promising sources of on-demand entanglement generation, their integration with silicon-based architectures remains a central challenge. Here, we demonstrate energy--time entanglement from a single InGaAs/GaAs quantum dot monolithically grown on a silicon substrate. Under coherent two-photon excitation, we achieve coherent control of the biexciton--exciton cascade, evidenced by Rabi oscillations and dressed-state formation. Using a four-channel Franson interferometer, we observe phase-dependent two-photon interference with visibilities up to $(64.0 \pm 7.0)\%$ for an 80 ps integration window (and $(49.4 \pm 1.9)\%$ for a 1600 ps window), approaching the threshold for Bell inequality violation at short time scales. These results establish monolithically integrated III--V-on-silicon quantum dots as promising sources of energy--time entangled photons for scalable quantum photonic technologies.

cond-mat.mes-hall↗

arXiv2026

Monolithic axial InGaAs quantum dot emitters in GaAs-based nanowires via Sb-mediated facet engineering

GaAs-based nanowires hosting active quantum heterostructures provide a promising route toward monolithic integration of single-photon sources on silicon, a key requirement for scalable quantum photonics. However, ultrathin axial quantum-emitter formation is often hindered by facet-dependent growth dynamics and rotational twins, which induce lateral overgrowth and compromise interface abruptness. Here, we develop InGaAs-based quantum emitters by tailoring facet evolution via dilute Sb incorporation, which efficiently suppresses twins and promotes confined axial insertion at the growth-front facet. This approach significantly enhances the probability of obtaining abrupt, few-nanometer-thin quantum dots at the nanowire tip. Single-nanowire optical spectroscopy reveals intense, spatially localized emission from the active region with lifetimes as short as (0.51 $\pm$ 0.02) ns, and second-order photon-correlation measurements consistently exhibit pronounced antibunching with $g^{(2)}(0)<0.4$, confirming single-photon emission. These results establish a strong correlation between twin density and axial heterostructure formation, identifying defect control as a key factor in realizing monolithically integrated nanowire single-photon sources.

physics.app-ph↗

arXiv2026

Localized Excitonic Emission in Wafer-Scale MOCVD-Grown GaSe 2D Nanosheets for Classical and Non-Classical Light Sources

Wafer-scale growth of two-dimensional semiconductors remains a key challenge for their integration into photonic technologies. While most studies of two-dimensional semiconductors have focused on transition metal dichalcogenides and their scalable fabrication, comparatively little attention has been given to III-VI monochalcogenides. Here, we report wafer-scale growth of gallium selenide (GaSe) by metal-organic chemical vapor deposition (MOCVD) and investigate its structural and optical properties for visible-range classical and quantum light emission. Two samples with thicknesses ranging from a few monolayers to several micrometers, controlled via the growth time, were investigated. The 30-minute grown sample yields intense, broad photoluminescence spanning 1.7--2.0$\,$eV, whereas the thinner 3-minute sample exhibits discrete narrow emission lines and single-photon emission with $(g^{(2)}(0) = 0.15 \pm 0.10)$. Remarkably, cathodoluminescence mapping reveals pronounced spatial localization of both spectrally narrow and broad emission centers. Together with temperature-dependent power-law analysis and Raman mapping, our results indicate defect-induced emission rather than intrinsic excitonic recombination. These findings establish wafer-scale MOCVD grown 2D GaSe as a platform for classical and non-classical light sources and highlight defect-engineered localization as a route toward scalable quantum photonics.

cond-mat.mes-hall↗

arXiv2026

Strain-Engineered Deterministic Quantum Dots for Telecom O-Band Emission Using Buried Stressors

The deterministic realization of quantum light sources operating at telecom wavelengths is essential for long-distance fiber-based quantum communication and distributed quantum computing. In this work, we demonstrate that telecom O-band emission can be achieved from site-controlled InGaAs/GaAs quantum dots (QDs). Our concept utilizes a buried AlAs/Al$_2$O$_3$ stressor layer with the unique feature that induces a well-defined and controllable tensile strain field at the growth surface, enabling both a redshift of QD emission to the $\sim$1.3~μm range and site-selective nucleation at the mesa centers. This concept eliminates not only the need for strain-reducing layers (SRLs), which are known to degrade optical coherence, but also provides spatial control and spectral tunability. The grown telecom QDs show pure single-photon emission with $g^{(2)}(τ) = (5.0 \pm 1.0) \times 10^{-2}$ at 4 K and $(2.8 \pm 0.3) \times 10^{-1}$ at 77~K, demonstrating the quantum nature and thermal stability of the emitters. The emission characteristics of complex excitonic states are analyzed using 8-band $k \cdot p$ and configuration-interaction modeling, which quantitatively reproduces the experimental observations. Finally, we present a theory-supported strategy to further redshift the emission toward the center of the O-band and beyond by employing a multi-buried-stressor approach. This combined framework of experiment and theory establishes the buried stressor concept as a scalable route toward highly coherent, position-controlled O-band quantum emitters compatible with industrial photonic integration.

cond-mat.mes-hall↗

arXiv2026

Probing Interface-Driven Mechanisms of Non-Classical Light in van der Waals Heterostructures

Single-photon emitters in two-dimensional semiconductors offer a versatile platform for integrated quantum photonics, yet their performance is strongly influenced by local dielectric environments and substrate-induced disorder. Here, we examine SPEs in monolayer WSe$_2$ incorporated into hBN/WSe$_2$/Clinochlore van der Waals heterostructures and assess how interface-mediated dielectric modulation governs their optical and quantum characteristics. Low-temperature micro-photoluminescence reveals narrow emission lines (100 - 300 $μ$eV) and robust non-classical behavior, with $g^{(2)}(0) = 0.13 \pm 0.02$ on SiO$_2$ and $0.54 \pm 0.02$ for emitters directly coupled to Clinochlore. Magneto-optical measurements yield effective g-factors near -8, consistent with defect states hybridized with dark excitons. WSe$_2$ on Clinochlore exhibits up to a fivefold enhancement in emission intensity, attributed to coupling with Fe-related substrate states that introduce resonant absorption near 1.75 eV. Kelvin probe force microscopy confirms strong dielectric contrast across thin and thick Clinochlore regions. Time-resolved photoluminescence shows that emitters on SiO$_2$ display a single $\approx 4$ ns lifetime, whereas those on Clinochlore exhibit biexponential dynamics with sub-nanosecond and tens-of-nanoseconds decay components. A phenomenological model incorporating coupling to bright and dark Fe-related states in Clinochlore accounts for modified excitation pathways. These results establish interface dielectric engineering in vdW heterostructures as an effective strategy for tailoring the radiative dynamics and brightness of quantum emitters in atomically thin materials.

cond-mat.mtrl-sci↗

arXiv2025

Scalable Quantum Photonic Platform Based on Site-Controlled Quantum Dots Coupled to Circular Bragg Grating Resonators

The scalable integration of solid-state quantum emitters into photonic nanostructures remains a central challenge for quantum photonic technologies. Here, we demonstrate a robust and streamlined integration strategy that tackles the long-standing issue of deterministic fabrication on randomly positioned self-assembled quantum dots (QDs), leveraging a buried-stressor-based site-controlled InGaAs QD platform. We show that this deterministic growth approach enables precise spatial alignment with circular Bragg grating (CBG) resonators for enhanced emission, eliminating the need for complex and time-consuming deterministic lithography techniques. We fabricated a $6\times6$ SCQD-CBG array with 100\% device yield, with 35 devices falling within the radial-offset range where the simulated photon-extraction efficiency (PEE) exceeds 20\%, underscoring the spatial precision and scalability of our fabrication concept. A systematically selected subset of five devices with varying radial displacements reveals clear offset-dependent trends in extraction efficiency, spectral linewidth, and photon indistinguishability, thereby establishing quantitative bounds on spatial alignment tolerances. In the best-aligned QD-CBG device, we achieve a PEE of $(47.1\pm3.8)\%$, a linewidth of $(1.41\pm0.22)$ GHz, a radiative decay lifetime of $(0.80\pm0.02)$~ns, a single-photon purity of $(99.58\pm0.18)\%$, and a Hong-Ou-Mandel two-photon interference visibility of $(81\pm5)\%$ under quasi-resonant excitation at saturation power. We confirm our conceptual understanding of the effect of emitter-position dependent charge-noise fluctuations in terms of a quantum-optical model for the (quantum-)emission properties.

cond-mat.mes-hall↗

arXiv2025

High Purcell enhancement in all-TMDC nanobeam resonator designs with active monolayers for nanolasers

We propose a nanobeam resonator incorporating an active monolayer, designed to achieve a high Purcell enhancement. The resonator is fully composed of transition-metal-dichalcogenide materials and intended to operate as a high-beta-factor nanolaser. A theoretical framework that models and optimizes the Purcell enhancement associated with the emission from atomically thin layers is developed. This framework is based on a resonance expansion, enabling spectral resolution of physical quantities governed by high-Q resonances. The numerical optimization of the resonator leads to the presence of a high-Q resonance supporting a strong electric field confinement in the monolayer to maximize the modal gain.

physics.optics↗

arXiv2025

Direct Epitaxial Growth and Deterministic Device Integration of high-quality Telecom O-Band InGaAs Quantum Dots on Silicon Substrate

Semiconductor quantum dots (QDs) are key building blocks for photonic quantum technologies, enabling practical sources of non-classical light. A central challenge for scalable integration is the direct epitaxial growth of high-quality emitters on industry-compatible silicon platforms. Furthermore, for long-distance fiber-based quantum communication, emission in the telecom O- or C-band is essential. Here, we demonstrate the direct growth of high-quality InGaAs/GaAs QDs emitting in the telecom O-band using a strain-reducing layer approach on silicon. Deterministic integration of individual QDs into circular Bragg grating resonators is achieved via in-situ electron-beam lithography. The resulting devices exhibit strong out-coupling enhancement, with photon extraction efficiencies up to $(40 \pm 2)\%$, in excellent agreement with numerical simulations. These results highlight the high material quality of both the epitaxial platform and the photonic nanostructure, as well as the precise lateral positioning of the emitter within 20~nm of the resonator center. At cryogenic temperature (4~K) and low excitation power ($0.027\times P_\text{sat}$), the devices show excellent single-photon purity, exceeding 99\%. Operation at elevated temperatures of 40~K and 77~K, compatible with compact Stirling cryo-coolers and liquid-nitrogen cooling, reveals robust performance, with single-photon purity maintained at $(88.4 \pm 0.6)\%$ at 77~K. These results demonstrate a practical and scalable route toward silicon-based quantum light sources and provide a promising path for cost-effective fabrication and seamless integration of quantum photonics with classical electronics, representing an important step toward large-scale, chip-based quantum information systems.

cond-mat.mes-hall↗

arXiv2024

Electrical manipulation of intervalley trions in twisted MoSe$_2$ homobilayers at room temperature

The impressive physics and applications of intra- and interlayer excitons in a transition metal dichalcogenide twisted-bilayer make these systems compelling platforms for exploring the manipulation of their optoelectronic properties through electrical fields. This work studies the electrical control of excitonic complexes in twisted MoSe$_2$ homobilayer devices at room temperature. Gate-dependent micro-photoluminescence spectroscopy reveals an energy tunability of several meVs originating from the emission of excitonic complexes. Furthermore, our study investigates the twist-angle dependence of valley properties by fabricating devices with stacking angles of $θ\sim1\degree$, $θ\sim4\degree$ and $θ\sim18\degree$. Strengthened by density functional theory calculations, the results suggest that, depending on the twist angle, the conduction band minima and hybridized states at the \textbf{Q}-point promote the formation of intervalley hybrid trions involving the \textbf{Q}-and \textbf{K}-points in the conduction band and the \textbf{K}-point in the valence band. By revealing the gate control of exciton species in twisted homobilayers, our findings open new avenues for engineering multifunctional optoelectronic devices based on ultrathin semiconducting systems.

cond-mat.mtrl-sci↗

arXiv2024

Enhancement of interlayer exciton emission in a TMDC heterostructure via a multi-resonant chirped microresonator up to room temperature

We report on multi-resonance chirped distributed Bragg reflector (DBR) microcavities. These systems are employed to investigate the light-mater interaction with both intra- and inter-layer excitons of transition metal dichalcogenide (TMDC) bilayer heterostructures. The chirped DBRs consisting of SiO2 and Si3N4 layers with gradually changing thickness exhibit a broad stopband with a width exceeding 600 nm. Importantly, and in contrast to conventional single-resonance microcavities, our structures provide multiple resonances across a broad spectral range, which can be matched to spectrally distinct resonances of the embedded TMDC heterostructures. We study cavity-coupled emission of both intra- and inter-layer excitons from an integrated WSe2/MoSe2 heterostructure in a chirped microcavity system. We observe an enhanced interlayer exciton emission with a Purcell factor of 6.67 +- 1.02 at 4 K. Additionally, we take advantage of cavity-enhanced emission of the interlayer exciton to investigate its temperature-dependent luminescence lifetime, which yields a value of 60 ps at room temperature. Our approach provides an intriguing platform for future studies of energetically distant and confined excitons in different semiconducting materials, which paves the way for various applications such as microlasers and single-photon sources by enabling precise control and manipulation of excitonic interactions utilizing multimode resonance light-matter interaction.

cond-mat.mes-hall↗

arXiv2023

High-$β$ lasing in photonic-defect semiconductor-dielectric hybrid microresonators with embedded InGaAs quantum dots

We report an easy-to-fabricate microcavity design to produce optically pumped high-$β$ quantum dot microlasers. Our cavity concept is based on a buried photonic-defect for tight lateral mode confinement in a quasi-planar microcavity system, which includes an upper dielectric distributed Bragg reflector (DBR) as a promising alternative to conventional III-V semiconductor DBRs. Through the integration of a photonic-defect, we achieve low mode volumes as low as 0.28 $μ$m$^3$, leading to enhanced light-matter interaction, without the additional need for complex lateral nanoprocessing of micropillars. We fabricate semiconductor-dielectric hybrid microcavities, consisting of Al$_{0.9}$Ga$_{0.1}$As/GaAs bottom DBR with 33.5 mirror pairs, dielectric SiO$_{2}$/SiN$_x$ top DBR with 5, 10, 15, and 19 mirror pairs, and photonic-defects with varying lateral size in the range of 1.5 $μ$m to 2.5 $μ$m incorporated into a one-$λ/n$ GaAs cavity with InGaAs quantum dots as active medium. The cavities show distinct emission features with a characteristic photonic defect size-dependent mode separation and \emph{Q}-factors up to 17000 for 19 upper mirror pairs in excellent agreement with numeric simulations. Comprehensive investigations further reveal lasing operation with a systematic increase (decrease) of the $β$-factor (threshold pump power) with the number of mirror pairs in the upper dielectric DBR. Notably, due to the quasi-planar device geometry, the microlasers show high temperature stability, evidenced by the absence of temperature-induced red-shift of emission energy and linewidth broadening typically observed for nano- and microlasers at high excitation powers.

physics.optics↗

arXiv2023

Low-threshold lasing of optically pumped micropillar lasers with Al$_{0.2}$Ga$_{0.8}$As/Al$_{0.9}$Ga$_{0.1}$As distributed Bragg reflectors

We report on the design, realization and characterization of optically pumped micropillar lasers with low-absorbing Al$_{0.2}$Ga$_{0.8}$As/Al$_{0.9}$Ga$_{0.1}$As dielectric Bragg reflectors (DBRs) instead of commonly used GaAs/AlGaAs DBRs. A layer of (In, Ga)As quantum dots (QDs) is embedded in the GaAs $λ$-cavity of as an active medium. We experimentally study the lasing characteristics of the fabricated micropillars by means of low-temperature photoluminescence with varying pump laser's wavelength between 532 nm and 899 nm. The incorporation of 20% Al content in the DBRs opens an optical pumping window from 700 nm to 820 nm, where the excitation laser light can effectively reach the GaAs cavity above its bandgap, while remaining transparent to the DBRs. This results in a substantially improved pump efficiency, a low lasing threshold, and a high thermal stability. Pump laser wavelengths outside of the engineered spectral window lead to low pump efficiency due to strong absorption by the top DBR, or inefficient excitation of pump-level excitons, respectively. The superiority of the absorption-free modified DBRs is demonstrated by simply switching the pump laser wavelength from 671 nm to 708 nm, which crosses the DBRs absorption edge and drastically reduces the lasing threshold by more than an order of magnitude from (363.5 $\pm$ 18.5) $μ$W to (12.8 $\pm$ 0.3) $μ$W.

cond-mat.mes-hall↗