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Can Wang

Bio: Can Wang is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Ferroelectricity & Thin film. The author has an hindex of 8, co-authored 18 publications receiving 181 citations.

Papers
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Journal ArticleDOI
TL;DR: A team of Chinese researchers have developed a topological laser made from a two-dimensional photonic crystal nanocavity slab with a lasing threshold of about one micro-watt and high spontaneous emission coupling factor of 0.25, which is comparable to the performance of conventional semiconductor lasers.
Abstract: The topological lasers, which are immune to imperfections and disorders, have been recently demonstrated based on many kinds of robust edge states, being mostly at microscale. The realization of 2D on-chip topological nanolasers, having the small footprint, low threshold and high energy efficiency, is still to be explored. Here, we report on the first experimental demonstration of the topological nanolaser with high performance in 2D photonic crystal slab. Based on the generalized 2D Su-Schrieffer-Heeger model, a topological nanocavity is formed with the help of the Wannier-type 0D corner state. Laser behaviors with low threshold about 1 $\mu W$ and high spontaneous emission coupling factor of 0.25 are observed with quantum dots as the active material. Such performance is much better than that of topological edge lasers and comparable to conventional photonic crystal nanolasers. Our experimental demonstration of the low-threshold topological nanolaser will be of great significance to the development of topological nanophotonic circuitry for manipulation of photons in classical and quantum regimes.

107 citations

Journal ArticleDOI
TL;DR: In this article, a topological photonic crystal cavity is designed and fabricated into GaAs slabs with quantum dots embedded, and the enhancement of photoluminescence intensity and emission rate are both observed when the quantum dot is on resonance with the corner state.
Abstract: Topological photonics provides a new paradigm in studying cavity quantum electrodynamics with robustness to disorder. In this work, we demonstrate the coupling between single quantum dots and the second-order topological corner state. Based on the second-order topological corner state, a topological photonic crystal cavity is designed and fabricated into GaAs slabs with quantum dots embedded. The coexistence of corner state and edge state with high quality factor close to 2000 is observed. The enhancement of photoluminescence intensity and emission rate are both observed when the quantum dot is on resonance with the corner state. This result enables the application of topology into cavity quantum electrodynamics, offering an approach to topological devices for quantum information processing.

68 citations

Journal ArticleDOI
TL;DR: In this article, a polycrystalline BiFeO3 (BFO) thin film on a transparent substrate also has the ferroelectric switchable diode and photovoltaic effects.

28 citations

Journal ArticleDOI
TL;DR: In this paper, three types of defect-related quantum emitters in monolayer tungsten diselenide (WSe$_2$) are observed, with different exciton g factors of 2.02, 9.36 and unobservable Zeeman shift, respectively.
Abstract: Monolayer transition metal dichalcogenides have recently attracted great interests because the quantum dots embedded in monolayer can serve as optically active single photon emitters. Here, we provide an interpretation of the recombination mechanisms of these quantum emitters through polarization-resolved and magneto-optical spectroscopy at low temperature. Three types of defect-related quantum emitters in monolayer tungsten diselenide (WSe$_2$) are observed, with different exciton g factors of 2.02, 9.36 and unobservable Zeeman shift, respectively. The various magnetic response of the spatially localized excitons strongly indicate that the radiative recombination stems from the different transitions between defect-induced energy levels, valance and conduction bands. Furthermore, the different g factors and zero-field splittings of the three types of emitters strongly show that quantum dots embedded in monolayer have various types of confining potentials for localized excitons, resulting in electron-hole exchange interaction with a range of values in the presence of anisotropy. Our work further sheds light on the recombination mechanisms of defect-related quantum emitters and paves a way toward understanding the role of defects in single photon emitters in atomically thin semiconductors.

18 citations

Journal ArticleDOI
TL;DR: In this paper, a topological cavity based on slow light topological edge mode for broadband Purcell enhancement is proposed, which can be realized with a bearded interface between two topologically distinct valley photonic crystals, featuring greatly enhanced Purcell factor because of the increased local density of states.
Abstract: Slow light in topological valley photonic crystal structures offers new possibilities to enhance light-matter interaction. We report a topological cavity based on slow light topological edge mode for broadband Purcell enhancement. The topological edge modes with large group indices over 100 can be realized with a bearded interface between two topologically distinct valley photonic crystals, featuring the greatly enhanced Purcell factor because of the increased local density of states. In the slow light regime, the topological cavity supports much more cavity modes with higher quality factor than that in the fast light regime, which is both demonstrated theoretically and experimentally. We demonstrate the cavity enables the broadband Purcell enhancement together with substantial Purcell factor, benefiting from dense cavity modes with high quality factor in a wide spectral range. It has great benefit to the realization of high-efficiency quantum-dot-based single-photon sources and entangled-photon sources with less restriction on spectral match. Such topological cavity could serve as a significant building block toward the development of photonic integrated circuits with embedded quantum emitters.

17 citations


Cited by
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Journal Article
TL;DR: In this article, the authors demonstrate first room temperature and ultrabright single photon emission from a color center in two-dimensional multilayer hexagonal boron nitride.
Abstract: We demonstrate first room temperature, and ultrabright single photon emission from a color center in two-dimensional multilayer hexagonal boron nitride. Density Functional Theory calculations indicate that vacancy-related centers are a likely source of the emission.

706 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a two-step ELO (1S-ELO) technology, which significantly reduces the dislocation density to below 107 cm−2.
Abstract: Gallium nitride (GaN) is an extremely promising wide band gap semiconductor material for optoelectronics and high temperature, high power electronics. Actually, GaN is probably the most important semiconductor since silicon. However, achievement of its full potential has still been limited by a dramatic lack of suitable GaN bulk single crystals. GaN has a high melting temperature and a very high decomposition pressure; therefore it cannot be grown using conventional methods used for GaAs or Si like Czochraslski or Bridgman growths.Since there is no GaN bulk single crystal commercially available, all technological development of GaN-based devices relies on heteroepitaxy. Most of the current device structures are grown on sapphire or 6H-SiC. However, since their lattice parameters and thermal expansion coefficients are not well-matched to GaN, the epitaxial growth generates huge densities of defects, with threading dislocations (TDs) being the most prevalent (109–1011 cm−2). As a comparison, homoepitaxially grown GaAs exhibits ~102–104 dislocation cm−2, and homoepitaxial Si almost 0. Actually this large density of TDs in GaN drastically limits the performance and operating lifetime of nitride-based devices. Therefore, there is currently a tremendous technological effort to reduce these defects.Metal organic vapour phase epitaxy (MOVPE) is currently the most widely used technology. Actually, all optoelectronic commercial device structures are fabricated using MOVPE. In MOVPE, the most appropriate precursor for nitrogen is ammonia (NH3), whereas either trimethyl or triethylgallium may be used as a gallium source. MOVPE of GaN requires a high partial pressure of NH3, high growth temperatures (~1000–1100°C) and a growth chamber specially designed to avoid premature reactions between the ammonia and gallium alkyls. Since sapphire (or 6H-SiC) and GaN are highly mismatched, direct growth of GaN is impossible. Therefore, the growth of GaN on any substrate first requires the deposition of a buffer layer, which, to some extent, accommodates the mismatch. Using appropriate nucleation layers allows a reduction of the dislocation density to the low 108 cm−2 range.Though laser diodes (LDs) were demonstrated in the late 1990s with such defect layers, the real breakthrough in laser technology was the dramatic improvement of the LD lifetime at the end of 1997, with the lifetime reaching 10 000 h. This was made possible by implementation of epitaxial lateral overgrowth (ELO) technology, which significantly reduces the dislocation density to below 107 cm−2.In ELO technology, parts of the highly dislocated starting GaN are masked with a dielectric mask, after which growth is restarted. At the beginning of the second growth step, deposition only occurs within the openings, with no deposition observed on the mask. This is referred to as selective area epitaxy (SAE). The TDs are prevented from propagating into the overlayer by the dielectric mask, whereas GaN grown above the opening (coherent growth) keeps the same TD density as the template, at least during the early stages of growth.Currently, two main ELO technologies exist: the simpler one involves a single growth step on striped openings. In this one-step-ELO (1S-ELO), growth in the opening remains in registry with the GaN template underneath (coherent part), whereas the GaN over the mask extends laterally (wings). This leads to two grades, namely highly dislocated GaN, above the openings, and low dislocation density GaN, above the masks. With this technique, devices have to be fabricated on the wings. Conversely, in the two-step-ELO (2S-ELO) process, the growth conditions of the first step are monitored to obtain triangular stripes. Inside these stripes, the TDs arising from the templates are bent by 90° when they encounter the inclined lateral facet. In the second step, the growth conditions are modified to achieve full coalescence. In this 2S-ELO technology, only the coalescence boundaries are defective. ELO technology produces high quality GaN, with TD densities in the mid 106 cm−2, line widths of the low temperature photoluminescence near band gap recombination peaks below 1 meV, and deep electron trap concentration below 1014 cm−3 (compared with mid 1015 cm−3 in standard GaN). Numerous modifications of the ELO process have been proposed either to avoid technological steps (maskless ELO) or to improve it (pendeoepitaxy, PE). To further reduce the TD density, multiple-step-ELO and pendeo have also been implemented.However, even ELO quality GaN is not good enough for the next generation of LDs. ELO samples do not yet offer a full surface suitable for laser technology. What is needed for LDs with at least 30 mW output power is high quality freestanding GaN with TDs close to or even below 106 cm−2. To reach this crystalline perfection, elaborate technologies are currently being implemented. They, at some stage, involve TD reduction mechanisms occurring in the ELO process.Self-supported GaN with at least ELO quality at an affordable cost is believed to be the next breakthrough in GaN technology.

307 citations

Journal Article
TL;DR: In this paper, a combination of transmission electron microscopy, electrical measurements, and electrostatic calculations showed that flexoelectricity provides a means of tuning the physical properties of ferroelectric epitaxial thin films.
Abstract: We report on nanoscale strain gradients in ferroelectric HoMnO3 epitaxial thin films, resulting in a giant flexoelectric effect. Using grazing-incidence in-plane x-ray diffraction, we measured strain gradients in the films, which were 6 or 7 orders of magnitude larger than typical values reported for bulk oxides. The combination of transmission electron microscopy, electrical measurements, and electrostatic calculations showed that flexoelectricity provides a means of tuning the physical properties of ferroelectric epitaxial thin films, such as domain configurations and hysteresis curves.

285 citations

Book ChapterDOI
01 Oct 2013
TL;DR: Within a few lines, a simple dynamic model of the universe can be constructed that is offering a life environment to modules and modular systems.
Abstract: Within a few lines, a simple dynamic model of the universe can be constructed that is offering a life environment to modules and modular systems.

238 citations

Journal ArticleDOI
01 Dec 2021
TL;DR: In this paper, the authors highlight a few emerging trends in photonics that they think are likely to have major impact at least in the upcoming decade, spanning from integrated quantum photonics and quantum computing, through topological/non-Hermitian photonics, to AI-empowered nanophotonics and photonic machine learning.
Abstract: Let there be light–to change the world we want to be! Over the past several decades, and ever since the birth of the first laser, mankind has witnessed the development of the science of light, as light-based technologies have revolutionarily changed our lives. Needless to say, photonics has now penetrated into many aspects of science and technology, turning into an important and dynamically changing field of increasing interdisciplinary interest. In this inaugural issue of eLight, we highlight a few emerging trends in photonics that we think are likely to have major impact at least in the upcoming decade, spanning from integrated quantum photonics and quantum computing, through topological/non-Hermitian photonics and topological insulator lasers, to AI-empowered nanophotonics and photonic machine learning. This Perspective is by no means an attempt to summarize all the latest advances in photonics, yet we wish our subjective vision could fuel inspiration and foster excitement in scientific research especially for young researchers who love the science of light.

184 citations