arXiv subjects

Paweł Holewa

Publications and source records attributed to Paweł Holewa.

14 recordsLinked to original sources

arXiv2026

Telecom-band site-controlled quantum dots with engineered low fine-structure splitting

Deterministic quantum light sources emitting at telecom wavelengths with vanishing fine-structure splitting (FSS) are essential components for scalable quantum communication. While self-assembled Stranski-Krastanov (SK) quantum dots (QDs) are high-quality emitters, their random positioning and shape-induced anisotropy typically limit their use in entangled-photon applications. In this work, we demonstrate site-controlled SK growth where InAs/InP QDs nucleate at the symmetric apexes of truncated InP nanopyramids. Confining adatom diffusion to a small, symmetric nucleation area suppresses anisotropic growth, promoting the nucleation of highly symmetric QDs with FSS reduced to values below our statistically validated resolution limit of $9.2~μ$eV. At the same time, lithographically defined nucleation sites enable deterministic control of the QD position, overcoming the limitations of conventional SK growth. The high structural quality of single symmetric QDs is evidenced by the single-photon character of the emission ($g^{(2)}(0)=0.07^{+0.27}_{-0.07}$) spanning the S, C, and L telecom bands, with no evidence of lithography-induced defects affecting emission dynamics. These results demonstrate that tailoring QD symmetry through nanopyramid growth engineering provides a route toward site-controlled emitters suitable for entangled photon generation and integrated quantum photonics devices.

cond-mat.mes-hall↗

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

Efficient passivation of III-As(P) photonic interfaces

Surface effects can significantly impact the performance of nanophotonic and quantum photonic devices, especially as the device dimensions are reduced. In this work, we propose and investigate a novel approach to surface passivation to mitigate these challenges in photonic nanostructures with III-As(P) quantum wells defined by a dry etching process. The nanostructures are annealed under the phosphine (PH$_3$) ambient inside a metal-organic vapor phase epitaxy chamber to eliminate surface and subsurface defects induced during the dry etching and subsequent oxidation of the etched sidewalls. Moreover, encapsulation of the active material with a wider bandgap material allows for maintaining the band structure of the device, mitigating band bending effects. Our findings reveal an almost order of magnitude reduction in the surface recombination velocity from $2 \times 10^3 \, \mathrm{cm/s}$ for the PH$_3$ annealing compared to $1.5 \times 10^4 \, \mathrm{cm/s}$ for the non-passivated structures and $5 \times 10^3 \, \mathrm{cm/s}$ for the standard method based on (NH$_4$)$_2$S wet treatment followed by Al$_2$O$_3$ encapsulation. A further reduction to $5 \times 10^2 \, \mathrm{cm/s}$ is achieved for the InP-regrown samples. Additionally, we develop a model accounting for the impact of surface charges in the analysis of time-resolved photoluminescence curves and demonstrate that the proposed passivation method effectively reduces the surface charge density on the sidewalls of the studied quantum well-based photonic nanostructures.

physics.optics↗

arXiv2024

InAs/InP quantum dot based C-Band all-fiber plug-and-play triggered single-photon source integrated using micro-transfer printing

Fiber-based long-haul quantum communication would greatly benefit from a robust and deterministically integrated source of quantum state. Here, we report the design, fabrication, and optical characterization of InAs/InP quantum dots in the InP H1 point defect 2D photonic crystal cavity, integrated with the standard single-mode fiber using a micro-transfer printing technique. The device was placed in a compact cryocooler maintaining a cryogenic temperature of 15 K with single-photon emission characterized by $g^{(2)}(0)=0.14(14)$ and reliable and stable emission (intensity fluctuations given by a standard deviation $σ= 0.13$), so that an all-fiber based connection between two laboratory nodes through an open area was established and utilized for testing the quantum channel. In this way, we demonstrate a plug-and-play all-fiber single-photon source operating in the third telecom window, where standard telecommunication fiber networks can be used as a low-loss medium.

physics.optics↗

arXiv2024

Xenon plasma-focused ion beam milling as a method to deterministically fabricate bright and high-purity single-photon sources operating at C-band

Electron beam lithography is a standard method for fabricating photonic nanostructures around semiconductor quantum dots (QDs), which are crucial for efficient single and indistinguishable photon sources in quantum information processing. However, this technique lacks direct 3D control over the nanostructure shape, complicating the design and enlarging the 2D footprint to suppress in-plane photon leakage while directing photons into the collecting lens aperture. Here, we present an alternative approach to employ Xenon plasma-focused ion beam (Xe-PFIB) technology as a reliable method for the 3D shaping of photonic nanostructures containing low-density self-assembled InAs/InP quantum dots emitting in the C-band range of the 3rd telecommunication window. We explore both deterministic and non-deterministic fabrication approaches, resulting in mesas naturally shaped as truncated cones. As a demonstration, we fabricate mesas using a heterogeneously integrated structure with a QDs membrane atop an aluminum mirror and silicon substrate. Finite-difference time-domain (FDTD) simulations show that the angled sidewalls significantly increase photon extraction efficiency, achieving η = 0.89 for NA = 0.65. We demonstrate experimentally a high purity of pulsed single-photon emission (~99%) and a high extraction efficiency of η = 0.24, with the latter surpassing the highest reported values obtained using electron beam lithography in the C-band.

physics.optics↗

arXiv2024

High-throughput quantum photonic devices emitting indistinguishable photons in the telecom C-band

Single indistinguishable photons at telecom C-band wavelengths are essential for quantum networks and the future quantum internet. However, high-throughput technology for single-photon generation at 1550 nm remained a missing building block to overcome present limitations in quantum communication and information technologies. Here, we demonstrate the high-throughput fabrication of quantum-photonic integrated devices operating at C-band wavelengths based on epitaxial semiconductor quantum dots. Our technique enables the deterministic integration of single pre-selected quantum emitters into microcavities based on circular Bragg gratings. Respective devices feature the triggered generation of single photons with ultra-high purity and record-high photon indistinguishability. Further improvements in yield and coherence properties will pave the way for implementing single-photon non-linear devices and advanced quantum networks at telecom wavelengths.

quant-ph↗

arXiv2024

On-Demand Generation of Indistinguishable Photons in the Telecom C-Band using Quantum Dot Devices

Semiconductor quantum dots (QDs) enable the generation of single and entangled photons, useful for various applications in photonic quantum technologies. Specifically for quantum communication via fiber-optical networks, operation in the telecom C-band centered around 1550$\,$nm is ideal. The direct generation of QD-photons in this spectral range and with high quantum-optical quality, however, remained challenging. Here, we demonstrate the coherent on-demand generation of indistinguishable photons in the telecom C-band from single QD devices consisting of InAs/InP QD-mesa structures heterogeneously integrated with a metallic reflector on a silicon wafer. Using pulsed two-photon resonant excitation of the biexciton-exciton radiative cascade, we observe Rabi rotations up to pulse areas of $4π$ and a high single-photon purity in terms of $g^{(2)}(0)=0.005(1)$ and $0.015(1)$ for exciton and biexciton photons, respectively. Applying two independent experimental methods, based on fitting Rabi rotations in the emission intensity and performing photon cross-correlation measurements, we consistently obtain preparation fidelities at the $π$-pulse exceeding 80$\%$. Finally, performing Hong-Ou-Mandel-type two-photon interference experiments we obtain a photon-indistinguishability of the full photon wave packet of up to $35(3)\%$, representing a significant advancement in the photon-indistinguishability of single photons emitted directly in the telecom C-band.

quant-ph↗

arXiv2023

Heterogeneous integration of single InAs/InP quantum dots with the SOI chip using direct bonding

Quantum information processing with photons in small-footprint and highly integrated silicon-based photonic chips requires incorporating non-classical light sources. In this respect, self-assembled III-V semiconductor quantum dots (QDs) are an attractive solution, however, they must be combined with the silicon platform. Here, by utilizing the large-area direct bonding technique, we demonstrate the hybridization of InP and SOI chips, which allows for coupling single photons to the SOI chip interior, offering cost-effective scalability in setting up a multi-source environment for quantum photonic chips. We fabricate devices consisting of self-assembled InAs QDs embedded in the tapered InP waveguide (WG) positioned over the SOI-defined Si WG. Focusing on devices generating light in the telecom C-band compatible with the low-loss optical fiber networks, we demonstrate the light coupling between InP and SOI platforms by observing photons outcoupled at the InP-made circular Bragg grating outcoupler fabricated at the end of an 80 $μ$m-long Si WG, and at the cleaved edge of the Si WG. Finally, for a device with suppressed multi-photon generation events exhibiting 80% single photon generation purity, we measure the photon number outcoupled at the cleaved facet of the Si WG. We estimate the directional on-chip photon coupling between the source and the Si WG to 5.1%.

physics.optics↗

arXiv2023

Observation of room temperature excitons in an atomically thin topological insulator

Optical spectroscopy of ultimately thin materials has significantly enhanced our understanding of collective excitations in low-dimensional semiconductors. This is particularly reflected by the rich physics of excitons in atomically thin crystals which uniquely arises from the interplay of strong Coulomb correlation, spin-orbit coupling (SOC), and lattice geometry. Here we extend the field by reporting the observation of room temperature excitons in a material of non-trivial global topology. We study the fundamental optical excitation spectrum of a single layer of bismuth atoms epitaxially grown on a SiC substrate (hereafter bismuthene or Bi/SiC) which has been established as a large-gap, two-dimensional (2D) quantum spin Hall (QSH) insulator. Strongly developed optical resonances are observed to emerge around the direct gap at the K and K' points of the Brillouin zone, indicating the formation of bound excitons with considerable oscillator strength. These experimental findings are corroborated, concerning both the character of the excitonic resonances as well as their energy scale, by ab-initio \emph{GW} and Bethe-Salpeter equation calculations, confirming strong Coulomb interaction effects in these optical excitations. Our observations provide the first evidence of excitons in a 2D QSH insulator at room temperature, with excitonic and topological physics deriving from the very same electronic structure.

cond-mat.mtrl-sci↗

arXiv2021

Bright Quantum Dot Single-Photon Emitters at Telecom Bands Heterogeneously Integrated on Si

Whereas the Si photonic platform is highly attractive for scalable optical quantum information processing, it lacks practical solutions for efficient photon generation. Self-assembled semiconductor quantum dots (QDs) efficiently emitting photons in the telecom bands ($1460-1625$ nm) allow for heterogeneous integration with Si. In this work, we report on a novel, robust, and industry-compatible approach for achieving single-photon emission from InAs/InP QDs heterogeneously integrated with a Si substrate. As a proof of concept, we demonstrate a simple vertical emitting device, employing a metallic mirror beneath the QD emitter, and experimentally obtained photon extraction efficiencies of $\sim10\%$. Nevertheless, the figures of merit of our structures are comparable with values previously only achieved for QDs emitting at shorter wavelength or by applying technically demanding fabrication processes. Our architecture and the simple fabrication procedure allows for the demonstration of a single-photon generation with purity $\mathcal{P}>98\%$ at the liquid helium temperature and $\mathcal{P}=75\%$ at $80$ K.

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

Thermal stability of emission from single InGaAs/GaAs quantum dots at the telecom O-band

Single-photon sources are key building blocks in most of the emerging secure telecommunication and quantum information processing schemes. Semiconductor quantum dots (QD) have been proven to be the most prospective candidates. However, their practical use in fiber-based quantum communication depends heavily on the possibility of operation in the telecom bands and at temperatures not requiring extensive cryogenic systems. In this paper we present a temperature-dependent study on single QD emission and single-photon emission from metalorganic vapour-phase epitaxy-grown InGaAs/GaAs QDs emitting in the telecom O-band. Micro-photoluminescence studies reveal that trapped holes in the vicinity of a QD act as reservoir of carriers that can be exploited to enhance photoluminescence from trion states observed at elevated temperatures up to at least 80 K. The luminescence quenching is mainly related to the promotion of holes to higher states in the valence band and this aspect must be primarily addressed in order to further increase the thermal stability of emission. Photon autocorrelation measurements yield single photon emission with a purity of $g_{50\mathrm{K}}^{(2)}\left(0\right)=0.13$ up to 50 K. Our results imply that these nanostructures are very promising candidates for single-photon sources at elevated temperatures in the telecom O-band and highlight means for improvements in their performance.

cond-mat.mes-hall↗

arXiv2020

Optical and electronic properties of symmetric InAs/InGaAlAs/InP quantum dots formed by a ripening process in molecular beam epitaxy: a promising system for broad-range single-photon telecom emitters

We present a detailed experimental optical study supported by theoretical modeling of InAs quantum dots (QDs) embedded in an InAlGaAs barrier lattice-matched to InP(001) grown with the use of a ripening step in molecular beam epitaxy. The method leads to the growth of in-plane symmetric QDs of low surface density, characterized by a multimodal size distribution resulting in a spectrally broad emission in the range of $1.4-2.0$ $μ$m, essential for many near-infrared photonic applications. We find that, in contrast to the InAs/InP system, the multimodal distribution results here from a two-monolayer difference in QD height between consecutive families of dots. This may stem from the long-range ordering in the quaternary barrier alloy that stabilizes QD nucleation. Measuring the photoluminescence (PL) lifetime of the spectrally broad emission, we find a nearly dispersionless value of $1.3\pm0.3$ ns. Finally, we examine the temperature dependence of emission characteristics. We underline the impact of localized states in the wetting layer playing the role of carrier reservoir during thermal carrier redistribution. We determine the hole escape to the InAlGaAs barrier to be a primary PL quenching mechanism in these QDs.

cond-mat.mes-hall↗

arXiv2018

Enhanced photon-extraction efficiency from InGaAs/GaAs quantum dots in deterministic photonic structures at 1.3 μm fabricated by in-situ electron-beam lithography

The main challenge in the development of non-classical light sources remains their brightness that limits the data transmission and processing rates as well as the realization of practical devices operating in the telecommunication range. To overcome this issue, we propose to utilize universal and flexible in-situ electron-beam lithography and hereby, we demonstrate a successful technology transfer to telecom wavelengths. As an example, we fabricate and characterize especially designed photonic structures with strain-engineered single InGaAs/GaAs quantum dots that are deterministically integrated into disc-shaped mesas. Utilizing this approach, an extraction efficiency into free-space (within a numerical aperture of 0.4) of (10${\pm}$2) % has been experimentally obtained in the 1.3 μm wavelength range in agreement with finite-element method calculations.

cond-mat.mes-hall↗