Optoelectronic Quantum Research Articles

Metamaterial unipolar quantum optoelectronics for mid-infrared free-space optics

Metamaterial unipolar quantum optoelectronics for mid-infrared free-space optics

Bright excitons in black phosphorus.

Twisted layers of atoms provide a tunable playground for quantum optoelectronics.

Fluorescence by incoherently pumped polar quantum dot placed in a low-frequency monochromatic field

Abstract We studied spectral properties of high-frequency fluorescent radiation from a two-level quantum system with broken inversion spatial symmetry, which can be implemented as a model of a one-electron two-level asymmetric polar semiconductor quantum dot whose electric dipole moment operator has permanent unequal diagonal matrix elements. The case of the excitation of this system by incoherent pumping of some sort supplemented with an additional driving monochromatic field, which frequency is much lower than the optical transition frequency of the quantum dot, was considered. An analytical expression for the fluorescence spectrum as a function of the amplitude and frequency of the monochromatic driving field, as well as of the pumping intensity, was derived. We also discussed feasible practical applications of the effects under study in the field of quantum optics and optoelectronics for the generation of high-frequency radiation, possessing stationary equidistant spectrum, and for the control of the radiative properties of such nanodevices as spasers (dipole nanolasers).

Valley-Hybridized Gate-Tunable 1D Exciton Confinement in MoSe2.

Controlling excitons at the nanoscale in semiconductor materials represents a formidable challenge in the quantum photonics and optoelectronics fields. Monolayers of transition metal dichalcogenides (TMDs) offer inherent 2D confinement and possess significant exciton binding energies, making them promising candidates for achieving electric-field-based confinement of excitons without dissociation. Exploiting the valley degree of freedom associated with these confined states further broadens the prospects for exciton engineering. Here, we show electric control of light polarization emitted from one-dimensional (1D) quantum-confined states in MoSe2. Building on previous reports of tunable trapping potentials and linearly polarized emission, we extend this understanding by demonstrating how nonuniform in-plane electric fields enable in situ control of these effects and highlight the role of gate-tunable valley hybridization in these localized states. Their polarization is entirely engineered through either the 1D confinement potential's geometry or an out-of-plane magnetic field. Controlling nonuniform in-plane electric fields in TMDs enables control of the energy (up to five times its line width), polarization state (from circular to linear), and position of 1D confined excitonic states (5 nm V-1).

Ab initio methods applied to carbon-containing defects in hexagonal boron nitride

The functionalities activated by defect centers in solids are constantly growing, opening new avenues for sustainable future technologies. These may extend to quantum optoelectronics if suitable defect centers are created and their properties understood. Recent progress in developing quantum emitters in hexagonal boron nitride (hBN) associated with carbon impurities enabled the realization of such concepts in atomically thin films, where the defect centers exhibit an unprecedented level of sensitivity toward the environment. The complexity of defects, together with new control knobs provided by van der Waals technology, poses a challenge for theory to accurately predict the properties of defect centers and to match them with experimental results. Here, we review the ab initio methods applied to carbon-containing defect centers in hBN, exploring the predictive capabilities of different levels of theory for their structural and optoelectronic properties.

Unipolar quantum optoelectronics for high speed direct modulation and transmission in 8–14 µm atmospheric window

The large mid-infrared (MIR) spectral region, ranging from 2.5 µm to 25 µm, has remained under-exploited in the electromagnetic spectrum, primarily due to the absence of viable transceiver technologies. Notably, the 8–14 µm long-wave infrared (LWIR) atmospheric transmission window is particularly suitable for free-space optical (FSO) communication, owing to its combination of low atmospheric propagation loss and relatively high resilience to turbulence and other atmospheric disturbances. Here, we demonstrate a direct modulation and direct detection LWIR FSO communication system at 9.1 µm wavelength based on unipolar quantum optoelectronic devices with a unprecedented net bitrate exceeding 55 Gbit s−1. A directly modulated distributed feedback quantum cascade laser (DFB-QCL) with high modulation efficiency and improved RF-design was used as a transmitter while two high speed detectors utilizing meta-materials to enhance their responsivity are employed as receivers; a quantum cascade detector (QCD) and a quantum-well infrared photodetector (QWIP). We investigate system tradeoffs and constraints, and indicate pathways forward for this technology beyond 100 Gbit s−1 communication.

Low-Temperature Anodization: An Electrochemical Route to Tailored Nanostructures in Heavily Doped p-Type Silicon for Forming Quantum Dots

This study presents a pioneering electrochemical approach to tailor the anodization outcomes of heavily doped p-type silicon, a subset of low-resistivity semiconductor materials, via low-temperature anodization. Conventionally, anodizing such silicon in hydrofluoric acid at room temperature leads to the formation of coarse porous silicon with negligible photoluminescence (PL) upon exposure to ultraviolet (UV) radiation.In this investigation, we embark on an unconventional path by conducting the anodization process at an exceptionally low temperature of -20°C. This seemingly subtle adjustment, however, triggers a remarkable transformation in the optical characteristics of the silicon substrate. Strikingly, the anodized surface, when illuminated with UV radiation, emits a vibrant and distinct red PL signal (Figure 1), signifying the emergence of quantum confinement effects attributable to nanocrystals, i.e., quantum dots.To substantiate the existence of these nanostructures, we employ advanced characterization techniques, with a focus on transmission electron microscopy (TEM). These rigorous analyses confirm the presence of well-defined silicon nanocrystals, typically measuring within the 3~4 nm range (Figure 2), meeting the prerequisites for quantum confinement effects. Notably, it is worth mentioning that the formation of such nanostructures is unattainable on heavily boron-doped silicon due to its high etching rate.In conclusion, our findings underscore the potential of low-temperature anodization as a versatile tool to tailor the luminescent properties of porous silicon at the nanoscale. This breakthrough not only advances our fundamental comprehension of semiconductor electrochemistry but also holds the promise of driving progress in electrochemical fabricating semiconductor quantum dots and optoelectronics. Figure 1

Bulk photovoltaic effect and high mobility in the polar 2D semiconductor SnP2Se6.

The growth of layered 2D compounds is a key ingredient in finding new phenomena in quantum materials, optoelectronics, and energy conversion. Here, we report SnP2Se6, a van der Waals chiral (R3 space group) semiconductor with an indirect bandgap of 1.36 to 1.41 electron volts. Exfoliated SnP2Se6 flakes are integrated into high-performance field-effect transistors with electron mobilities >100 cm2/Vs and on/off ratios >106 at room temperature. Upon excitation at a wavelength of 515.6 nanometer, SnP2Se6 phototransistors show high gain (>4 × 104) at low intensity (≈10-6 W/cm2) and fast photoresponse (< 5 microsecond) with concurrent gain of ≈52.9 at high intensity (≈56.6 mW/cm2) at a gate voltage of 60 V across 300-nm-thick SiO2 dielectric layer. The combination of high carrier mobility and the non-centrosymmetric crystal structure results in a strong intrinsic bulk photovoltaic effect; under local excitation at normal incidence at 532 nm, short circuit currents exceed 8 mA/cm2 at 20.6 W/cm2.

Room-Temperature Polariton Lasing from CdSe Core-Only Nanoplatelets.

This paper reports how CdSe core-only nanoplatelets (NPLs) coupled with plasmonic Al nanoparticle lattices can exhibit exciton-polariton lasing. By improving a procedure to synthesize monodisperse 4-monolayer CdSe NPLs, we could resolve polariton decay dynamics and pathways. Experiment and theory confirmed that the system is in the strong coupling regime based on anticrossings in the dispersion diagrams and magnitude of the Rabi-splitting values. Notably, polariton lasing is observed only for cavity lattice periodicities that exhibit specific dispersive characteristics that enable polariton accumulation. The threshold of polariton lasing is 25-fold lower than the reported photon lasing values from CdSe NPLs in similar cavity designs. This open-cavity platform offers a simple approach to control exciton polaritons anticipated to benefit quantum information processing, optoelectronics, and chemical reactions.

Spatial photoluminescence and lifetime mappings of quasi-2D perovskites coupled with a dielectric metasurface.

Light-matter interaction between quantum emitters and optical cavities plays a vital role in fundamental quantum photonics and the development of optoelectronics. Resonant metasurfaces are proven to be an efficient platform for tailoring the spontaneous emission (SE) of the emitters. In this work, we study the interplay between quasi-2D perovskites and dielectric TiO2 metasurfaces. The metasurface, functioning as an open cavity, enhances electric fields near its plane, thereby influencing the emissions of the perovskite. This is verified through angle-resolved photoluminescence (PL) studies. We also conducted reflectivity measurements and numerical simulations to validate the coupling between the quasi-2D perovskites and photonic modes. Notably, our work introduces a spatial mapping approach to study Purcell enhancement. Using fluorescence lifetime imaging microscopy (FLIM), we directly link the PL and lifetimes of the quasi-2D perovskites in spatial distribution when positioned on the metasurface. This correlation provides unprecedented insights into emitter distribution and emitter-resonator interactions. The methodology opens a new (to the best of our knowledge) approach for studies in quantum optics, optoelectronics, and medical imaging by enabling spatial mapping of both PL intensity and lifetime, differentiating between uncoupled quantum emitters and those coupled with different types of resonators.

Estimation enhancing in optoelectronic property: A novel approach using orbital interaction parameters and tight-binding

This paper advocates for an innovative approach designed for estimating optoelectronic properties of quantum structures utilizing Tight-Binding (TB) theory. Predicated on the comparative analysis between estimated and actual properties, the study strives to validate the efficacy of this proposed technique; focusing notably on the computation of bandgap energy. It is observed that preceding methodologies offered a restricted accuracy when predicting complex structures like super-lattices and quantum wells. To address this gap, we propose a methodology involving three distinct phases using orbital interaction parameters (OIPs) and the TB theory. The research employed Aluminium Arsenide (AlAs) and Gallium Arsenide (GaAs) as the primary bulk materials. Our novel approach introduces a computation framework that first focuses on bulk computation, subsequently expanding to super-lattice structures. The findings of this research demonstrate promising results regarding the accuracy of predicated optoelectronic properties, particularly the cut-off wavelength. This study paves the way for future research, potentially enhancing the precision of the proposed methodology and its application scope within the field of quantum optoelectronics.

Coherent electronic coupling in quantum dot solids induces cooperative enhancement of nonlinear optoelectronic responses.

Synchronized dynamics of quantum dot (QD) ensembles are essential for generating ultrafast and giant optical responses beyond those of individual QDs. Increasing the strength of the direct electronic coupling between QDs is a key strategy for the realization of cooperative quantum phenomena. Here, we observe a quantum cooperative effect on nonlinear photocurrents caused by the coherent electronic coupling in semiconductor QD solids. We measure quantum interference signals cooperatively generated in QD solids. We control the inter-QD distance with atomic precision using bidentate ligands that strongly link the QDs. The harmonic quantum interference signals are strongly enhanced when shortening the molecular length of the ligand. Furthermore, we clarify that the coherence length of multiexcitons extends to neighbouring QDs. This finding is direct evidence that multiexciton coherent tunnelling assists the ultrafast exciton delocalization. Cooperative enhancement in QD solids may find application in advanced quantum optoelectronics.

Exploring Mid-IR FSO Communications With Unipolar Quantum Optoelectronics

Exploring Mid-IR FSO Communications With Unipolar Quantum Optoelectronics

Uncovering the Mechanisms of Triplet-Triplet Annihilation Upconversion Enhancement via Plasmonic Nanocavity Tuning.

The nonlinear conversion of photons from lower to higher energy is important for a wide range of applications, from quantum communications and optoelectronics to solar energy conversion and medicine. Triplet-triplet annihilation upconversion (TTA UC), which utilizes an absorber/emitter molecular pair, is a promising tool for upconversion applications requiring low intensity light such as photovoltaics, photocatalysis, and bioimaging. Despite demonstrations of efficient TTA UC in solution, practical applications have proven difficult, as thin films retard the necessary energy transfer steps and result in low emission yields. In this work, TTA UC emission from a thin film is greatly enhanced through integration into plasmonic nanogap cavities consisting of a silver mirror, a nanometer-scale polymer spacer containing a TTA molecular pair, and colloidally synthesized silver nanocubes. Mechanistic studies performed by varying the nanocube side length (45-150 nm) to tune the nanogap cavity resonance paired with simulations reveal absorption rate enhancement to be the primary operative mechanism in overall TTA UC emission enhancement. This absorption enhancement decreases the TTA UC threshold intensity by an order of magnitude and allows TTA UC emission to be excited with light up to 120 nm redder than the usable wavelength range for the control samples. Further, combined nanogap cavities composed of two distinct nanocube sizes result in surfaces which simultaneously enhance the absorption rate and emission rate. These dual-size nanogap cavities result in 45-fold TTA UC emission enhancement. In total, these studies present TTA UC emission enhancement, illustrate how the usable portion of the spectrum can be expanded for a given sensitizer-emitter pair, and develop both mechanistic understanding and design rules for TTA UC emission enhancement by plasmonic nanostructures.

Stable electroluminescence in ambipolar dopant-free lateral p–n junctions

Dopant-free lateral p–n junctions in the GaAs/AlGaAs material system have attracted interest due to their potential use in quantum optoelectronics (e.g., optical quantum computers or quantum repeaters) and ease of integration with other components, such as single electron pumps and spin qubits. A major obstacle to integration has been the unwanted charge accumulation at the p–n junction gap that suppresses light emission, either due to enhanced non-radiative recombination or due to inhibition of p–n current. Typically, samples must frequently be warmed to room temperature to dissipate this built-up charge and restore light emission in a subsequent cooldown. Here, we introduce a practical gate voltage protocol that clears this parasitic charge accumulation, in situ at low temperature, enabling the indefinite cryogenic operation of devices. This reset protocol enabled the optical characterization of stable, bright, dopant-free lateral p–n junctions with electroluminescence linewidths among the narrowest (&amp;lt;1 meV; &amp;lt;0.5 nm) reported in this type of device. It also enabled the unambiguous identification of the ground state of neutral free excitons (heavy and light holes) as well as charged excitons (trions). The free exciton emission energies for both photoluminescence and electroluminescence are found to be nearly identical (within 0.2 meV or 0.1 nm). The binding and dissociation energies for free and charged excitons are reported. A free exciton lifetime of 237 ps was measured by time-resolved electroluminescence, compared to 419 ps with time-resolved photoluminescence.

Gate-modulated reflectance spectroscopy for detecting excitonic states in two-dimensional semiconductors

We have developed a microspectroscopy technique for measuring gate-modulated reflectance to probe excitonic states in two-dimensional transition metal dichalcogenides. Through the use of gate-modulated spectroscopy, we were able to detect excited states of excitons and trions, which would typically have weak optical signals in traditional reflectance spectroscopy. Using a transfer matrix method for spectral analysis, the binding energy of trion 2s was determined to be 26 meV. As observing the Rydberg series of excitonic states provides fruitful information on the strong Coulomb interaction in two-dimensional systems, gate-modulated spectroscopy can be a versatile tool for understanding underlying many-body physics as well as designing next-generation quantum optoelectronics based on two-dimensional materials.

Phase Diagram of High-Temperature Electron-Hole Quantum Droplet in Two-Dimensional Semiconductors.

Quantum liquids, systems exhibiting effects of quantum mechanics and quantum statistics at macroscopic levels, represent one of the most exciting research frontiers of modern physical science and engineering. Notable examples include Bose-Einstein condensation (BEC), superconductivity, quantum entanglement, and a quantum liquid. However, quantum liquids are usually only stable at cryogenic temperatures, significantly limiting fundamental studies and device development. Here we demonstrate the formation of stable electron-hole liquid (EHL) with the quantum statistic nature at temperatures as high as 700 K in monolayer MoS2 and elucidate that the high-temperature EHL exists as droplets in sizes of around 100-160 nm. We also develop a thermodynamic model of high-temperature EHL and, based on the model, compile an exciton phase diagram, revealing that the ionized photocarrier drives the gas-liquid transition, which is subsequently validated with experimental results. The high-temperature EHL provides a model system to enable opportunities for studies in the pursuit of other high-temperature quantum liquids. The results can also allow for the development of quantum liquid devices with practical applications in quantum information processing, optoelectronics, and optical interconnections.

A highly sensitive broadband superconducting thermoelectric single-photon detector

We propose a passive single-photon detector based on the bipolar thermoelectric effect occurring in tunnel junctions between two different superconductors thanks to spontaneous electron–hole symmetry breaking. Our superconducting thermoelectric detector (STED) converts a finite temperature difference caused by the absorption of a single photon into an open circuit thermovoltage. Designed with feasible parameters, our STED is able to reveal single photons of frequency ranging from ∼15 GHz to ∼150 PHz depending on the chosen design and materials. In particular, this detector is expected to show values of the signal-to-noise ratio SNR ∼ 15 at ν = 50 GHz when operated at a temperature of 10 mK. Interestingly, this device can be viewed as a digital single-photon detector, since it generates an almost constant voltage VS for the full operation energies. Our STED can reveal single photons in a frequency range wider than four decades with the possibility to discern the energy of the incident photon by measuring the time persistence of the generated thermovoltage. Its broadband operation suggests that our STED could find practical applications in several fields of quantum science and technology, such as quantum computing, telecommunications, optoelectronics, THz spectroscopy, and astro-particle physics.

Controlling quantum phases of electrons and excitons in moiré superlattices

Moiré lattices formed in twisted and lattice-mismatched van der Waals heterostructures have emerged as a platform to engineer the novel electronic and excitonic states at the nanoscale. This Perspective reviews the materials science of moiré heterostructures with a focus on the structural properties of the interface and its structural–property relationships. We first review the studies of the atomic relaxation and domain structures in moiré superlattices and how these structural studies provide critical insights into understanding the behaviors of quantum-confined electrons and excitons. We discuss the general frameworks to manipulate moiré structures and how such control can be harnessed for engineering new phases of matter and simulating various quantum phenomena. Finally, we discuss routes toward large-scale moiré heterostructures and give an outlook on their applications in quantum electronics and optoelectronics. Special emphasis will be placed on the challenges and opportunities of the reliable fabrication and dynamical manipulation of moiré heterostructures.

Atomic Hydrogen Annealing of Graphene on InAs Surfaces and Nanowires: Interface and Morphology Control for Optoelectronics and Quantum Technologies

Folding two-dimensional graphene around one-dimensional III–V nanowires yields a new class of hybrid nanomaterials combining their excellent complementary properties. However, important for high-quality electrical and optical performance, needed in many applications, are well-controlled oxide-free interfaces and a tight folding morphology. To improve the interface chemistry between the graphene and InAs, we annealed the samples in atomic hydrogen. Using surface-sensitive imaging, we found that the III–V native oxides in the interface can be reduced at temperatures that maintain the graphene and the III–V nanostructures. Transferring both single- and multilayer graphene flakes onto InAs NWs, we found that single layers fold tightly around the NWs, while the multilayers fold weakly with a decline of only a few degrees. Annealing in atomic hydrogen further tightens the folding. Together, this indicates that high-quality morphological and chemical control of this hybrid material system is possible, opening for future devices for quantum technologies and optoelectronics.