arXiv subjects

Shima Kadkhodazadeh

Publications and source records attributed to Shima Kadkhodazadeh.

11 recordsLinked to original sources

arXiv2026

A sulfonitride transparent conductive thin film with ultra-high refractive index

With the rise of AI-assisted materials screening, extraordinary properties are now frequently predicted in experimentally uncharted material systems, highlighting the need to develop new synthesis methods for unconventional materials beyond the classic bulk powder form. Here, we establish the first thin-film growth route for any metal sulfonitride compound by realizing Zr2SN2 films with a rare and compelling combination of optical and electrical properties. Zr2SN2 is transparent across most of the visible range while exhibiting a very high average refractive index of 2.95 in the visible, exceeding expectations based on conventional refractive index-bandgap scaling. Importantly, the same Zr2SN2 film shows degenerate n-type conductivity with carrier density above 10^20 cm-3 and intragrain mobility above 8 cm2V-1s-1, approaching those of established transparent conductive oxides. Zr2SN2 thus demonstrates that strong light-matter interaction, optical transparency and electrical conductivity can be reconciled within a single material platform, revealing a new class of high-refractive-index transparent conductors.

cond-mat.mtrl-sci↗

arXiv2026

Local droplet etching-assisted quantum dot epitaxy for telecom C-band quantum light emitters

Significant progress in quantum light sources for quantum communication applications requires reproducible and symmetric quantum emitters acting as single-photon sources capable of generating entangled photons on demand at specific telecom wavelengths. Here, we propose telecom-emitting epitaxial quantum dots (QDs) fabricated using the local droplet etching (LDE) approach. The resulting well-defined, low-density ($10^9$/cm$^2$) QDs based on In$_{x}$Ga$_{1-x}$As are formed in symmetric LDE nanoholes (in-plane aspect ratio of 1.14) in In$_{0.52}$Al$_{0.48}$As. Detailed transmission electron microscopy provides comprehensive insight into the structural integrity, interface quality, and compositional profiles of the QDs, which underpin their promising optical properties. Photoluminescence spectroscopy reveals narrow emission lines (0.2 meV) and high optical quality, while second-order autocorrelation measurements confirm clear single-photon emission, with $g^{(2)}(0)=0.07\pm0.02$ under above-band continuous-wave excitation and $g^{(2)}(0)=0.16 \pm 0.18$ under pulsed excitation. Precise numerical modeling, combining multiband $\boldsymbol{k} \cdot \boldsymbol{p}$ and configuration-interaction methods, supports the optical characterization and identifies thermal excitation pathways that explain the persistence of emission up to liquid-nitrogen temperatures. These results highlight the versatility of the LDE approach for integrating new material systems and pave the way toward scalable fabrication of quantum light sources with tailored emission properties.

physics.optics↗

arXiv2025

Monolithic Integration of Sub-50 nm III-V Nano-Heterostructures on Si (001) for Telecom Photonics

The demand for advanced photonics technology is increasing rapidly, fueled by the necessity for high-performance and cost-effective optical information processing systems extending into the quantum domain. Silicon, benefiting from its mature fabrication processes, stands as an ideal platform. However, its inherent indirect bandgap leads to inefficient light emission. The integration of III-V materials has been proven essential to overcome this drawback. These materials are recognized for their efficient light emission and superior bandgap engineering capabilities, making them indispensable in photonics and beyond. Here, we present the monolithic integration of small-volume III-V nanoheterostructures with silicon via selective area epitaxy in the pyramidal openings etched in (100)-oriented silicon substrate. The precise positioning of the nano-heterostructures is achieved using electron beam lithography. Our atomic resolution imaging and chemical analysis confirms the epitaxial nature of InP growth, revealing well-defined heterointerfaces. Each structure incorporates an InAsP quantum dot-like active medium, and the correlation of the growth parameters with the nanoscale structure was analyzed using advanced electron microscopy. The eight-band k.p calculations demonstrate energy level quantization in three spatial dimensions. Optical characterization shows that heterostructure emission can be engineered to cover the entire telecom wavelength range. Consequently, these InAsP/InP nano-heterostructures could serve as a gain medium for silicon-based hybrid nano-lasers and nano-LEDs and quantum light sources in the telecom wavelength range.

physics.optics↗

arXiv2025

On-chip integrated light sources with MoS2/WSe2 moiré superlattices at telecom wavelengths

On-chip integrated light sources are essential for photonic integrated circuits, requiring waveguides to interface various components, from light sources to detectors. Two-dimensional (2D) transition metal dichalcogenide (TMD) heterostructures offer exceptional tunability and direct bandgaps, opening new avenues for on-chip light sources. However, a waveguide-integrated light source based on 2D materials operating in the telecom windows has yet to be realized. In this work, we demonstrate that the creation of a moiré superlattice enables light emission in the optical fiber communication (OFC) O-band (1260-1360 nm) with brightness surpassing that of intralayer excitons in monolayer MoTe2. Furthermore, we realize waveguide-integrated light sources emitting in the O-band by integrating these superlattices with asymmetric nanobeam cavities. This cavity design not only significantly enhances light emission but also improves the spectral purity of the single cavity mode. Moreover, the device output remains remarkably stable across varying pump power in an ambient environment, demonstrating excellent operational stability. The device performance remains unchanged over a nine-month measurement period, highlighting its long-term stability. This work presents a new architecture for on-chip light sources, advancing practical photonic applications.

physics.optics↗

arXiv2023

Self-assembly of atomic-scale photonic cavities

Despite tremendous progress in the research on self-assembled nanotechnological building blocks such as macromolecules, nanowires, and two-dimensional materials, synthetic self-assembly methods bridging nanoscopic to macroscopic dimensions remain unscalable and inferior to biological self-assembly. In contrast, planar semiconductor technology has had an immense technological impact owing to its inherent scalability, yet it appears unable to reach the atomic dimensions enabled by self-assembly. Here we use surface forces including Casimir-van der Waals interactions to deterministically self-assemble and self-align suspended silicon nanostructures with void features well below the length scales possible with conventional lithography and etching, despite using nothing more than conventional lithography and etching. The method is remarkably robust and the threshold for self-assembly depends monotonically on all governing parameters across thousands of measured devices. We illustrate the potential of these concepts by fabricating nanostructures, which are impossible to make with any other known method: Waveguide-coupled high-Q silicon photonic cavities that confine telecom photons to 2 nm air gaps with an aspect ratio of 100, corresponding to mode volumes more than 100 times below the diffraction limit. Scanning transmission electron microscopy measurements confirm the ability to build devices even with subnanometer dimensions. Our work constitutes the first steps towards a new generation of fabrication technology that combines the atomic dimensions enabled by self-assembly with the scalability of planar semiconductors.

physics.optics↗

arXiv2023

Fine-tunable near-critical Stranski-Krastanov growth of InAs/InP quantum dots

Emerging applications of self-assembled semiconductor quantum dot (QD)-based nonclassical light sources emitting in the telecom C-band (1530 to 1565 nm) present challenges in terms of controlled synthesis of their low-density ensembles, critical for device processing with an isolated QD. This work shows how to control the surface density and size of InAs/InP quantum dots over a wide range by tailoring the conditions of Stranski-Krastanow growth. We demonstrate that in the near-critical growth regime, the density of quantum dots can be tuned between $10^7$ and $10^{10} cm^{-2}$. Furthermore, employing both experimental and modeling approaches, we show that the size (and therefore the emission wavelength) of InAs nanoislands on InP can be controlled independently from their surface density. Finally, we demonstrate that our growth method gives low-density ensembles resulting in well-isolated QD-originated emission lines in the telecom C-band.

cond-mat.mes-hall↗

arXiv2021

Droplet epitaxy symmetric InAs/InP quantum dots for quantum emission in the third telecom window: morphology, optical and electronic properties

The rapidly developing quantum communication technology requires deterministic quantum emitters that can generate single photons and entangled photon pairs in the third telecom window, in order to be compatible with existing optical fiber networks and on-chip silicon photonic processors. InAs/InP quantum dots (QDs) are among the leading candidates for this purpose, due to their high emission efficiency in the required spectral range. However, fabricating versatile InAs/InP QD-based quantum emitters is challenging, especially as these QDs typically have asymmetric profiles in the growth plane, resulting in a substantial bright-exciton fine structure splitting (FSS). This hinders the generation of entangled photon pairs and thus, compromises the versatility of InAs/InP QDs. We overcome this by implementing droplet epitaxy (DE) synthesis of low surface density (2.8$\times$10$^8$ cm$^{-2}$) InAs QDs on an (001)-oriented InP substrate. The resulting QDs are located in etched pits, have concave bases, and most importantly, have symmetric in-plane profiles. We provide an analytical model to explain the kinetics of pit formation and QD base shape modification. Our theoretical calculations of electronic states reveal the properties of neutral and charged excitons and biexcitons confined in such QDs, which agree with the optical investigations of individual QDs. The optical response of QD ensembles suggests that FSS may indeed be negligible, as reflected in the vanishing degree of linear polarization. However, single QD spectrum gathered from an etched mesa shows moderate FSS of (50$\pm$5) $μ$eV that we link to destructive changes made in the QD environment during the post-growth processing. Finally, we show that the studied DE QDs provide a close-to-ideal single-photon emission purity of (92.5$\pm$7.5) $\%$ in the third telecom window.

cond-mat.mes-hall↗

arXiv2020

Monolithic integration of InP on Si by molten alloy driven selective area epitaxial growth

We report a new approach for monolithic integration of III-V materials into silicon, based on selective area growth and driven by a molten alloy in metal-organic vapor epitaxy. Our method includes elements of both selective area and droplet-mediated growths and combines the advantages of the two techniques. Using this approach, we obtain organized arrays of high crystalline quality InP insertions into (100) oriented Si substrates. Our detailed structural, morphological and optical studies reveal the conditions leading to defect formation. These conditions are then eliminated to optimize the process for obtaining dislocation-free InP nanostructures grown directly on Si and buried below the top surface. The PL signal from these structures exhibits a narrow peak at the InP bandgap energy. The fundamental aspects of the growth are studied by modeling the InP nucleation process. The model is fitted by our x-ray diffraction measurements and correlates well with the results of our transmission electron microscopy and optical investigations. Our method constitutes a new approach for the monolithic integration of active III-V material into Si platform and opens up new opportunities in active Si photonics.

physics.app-ph↗

arXiv2015

Multipole plasmons and their disappearance in few-nanometer silver nanoparticles

In electron energy-loss spectroscopy (EELS) of individual silver nanoparticles encapsulated in silicon nitride, we observe besides the usual dipole resonance an additional surface plasmon (SP) resonance corresponding to higher angular momenta. We even observe both resonances for nanoparticle radii as small as 4 nm, where previously only the dipole resonance was assumed to play a role. Electron beams positioned outside of the particles mostly excite the dipole mode, but the higher-order resonance can even dominate the dipole peak when exciting at the particle surface, the usual choice for maximal EELS signal. This allows us to study the radius dependence of both resonances separately. For particles smaller than 4 nm, the higher-order SP mode disappears, in agreement with generalized nonlocal optical response (GNOR) theory, while the dipole resonance blueshift exceeds GNOR predictions. Unlike in optical spectra, multipole surface plasmons are important in EELS spectra even of ultra-small metallic nanoparticles.

physics.optics↗

arXiv2013

Extremely confined gap surface plasmon modes excited by electrons

High spatial and energy resolution EELS can be employed for detailed characterization of both localized and propagating surface plasmon excitations supported by metal nanostructures, giving insight into fundamental physical phenomena involved in various plasmonic effects. Here, applying EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface plasmon (GSP) modes excited by swift electrons in nanometer-wide gaps. Both experimental and theoretical EELS data reveal the resonance behavior associated with the excitation of the antisymmetric (with respect to the transverse electric-field component) GSP mode for extremely small gap widths, down to ~5 nm. It is argued that the excitation of this mode, featuring very strong absorption, plays a crucial role in the experimental realization of non-resonant light absorption by ultra-sharp convex grooves with fabrication-induced asymmetry. Occurrence of the antisymmetric GSP mode along with the fundamental GSP mode exploited in plasmonic waveguides with extreme light confinement is a very important factor that should be taken into account in the design of plasmonic nanophotonic circuits and devices.

cond-mat.mes-hall↗

arXiv2013

Blueshift of the surface plasmon resonance in silver nanoparticles studied with EELS

We study the surface plasmon (SP) resonance energy of isolated spherical Ag nanoparticles dispersed on a silicon nitride substrate in the diameter range 3.5-26 nm with monochromated electron energy-loss spectroscopy. A significant blueshift of the SP resonance energy of 0.5 eV is measured when the particle size decreases from 26 down to 3.5 nm. We interpret the observed blueshift using three models for a metallic sphere embedded in homogeneous background material: a classical Drude model with a homogeneous electron density profile in the metal, a semiclassical model corrected for an inhomogeneous electron density associated with quantum confinement, and a semiclassical nonlocal hydrodynamic description of the electron density. We find that the latter two models provide a qualitative explanation for the observed blueshift, but the theoretical predictions show smaller blueshifts than observed experimentally.in a homogeneous medium.

cond-mat.mes-hall↗