Showing papers on "Quantum well published in 2017"
TL;DR: It is reported that, counterintuitive to classical quantum-confined systems where photogenerated electrons and holes are strongly bound by Coulomb interactions or excitons, the photophysics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovkite-crystal units is dominated by lower-energy states associated with the local intrinsic electronic structure of the edges of the perovSKite layers.
Abstract: Understanding and controlling charge and energy flow in state-of-the-art semiconductor quantum wells has enabled high-efficiency optoelectronic devices. Two-dimensional (2D) Ruddlesden-Popper perovskites are solution-processed quantum wells wherein the band gap can be tuned by varying the perovskite-layer thickness, which modulates the effective electron-hole confinement. We report that, counterintuitive to classical quantum-confined systems where photogenerated electrons and holes are strongly bound by Coulomb interactions or excitons, the photophysics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovskite-crystal units (>1.3 nanometers) is dominated by lower-energy states associated with the local intrinsic electronic structure of the edges of the perovskite layers. These states provide a direct pathway for dissociating excitons into longer-lived free carriers that substantially improve the performance of optoelectronic devices.
798 citations
TL;DR: By coupling the as-prepared PQDs with microfiber evanescent light field, the PQD-based saturable absorber (SA) device exhibits ultrafast nonlinear saturable absorption property, with an optical modulation depth of 8.1% at the telecommunication band.
Abstract: We fabricate ultrasmall phosphorene quantum dots (PQDs) with an average size of 2.6 ± 0.9 nm using a liquid exfoliation method involving ultrasound probe sonication followed by bath sonication. By coupling the as-prepared PQDs with microfiber evanescent light field, the PQD-based saturable absorber (SA) device exhibits ultrafast nonlinear saturable absorption property, with an optical modulation depth of 8.1% at the telecommunication band. With the integration of the all-fiber PQD-based SA, a continuous-wave passively mode-locked erbium-doped (Er-doped) laser cavity delivers stable, self-starting pulses with a pulse duration of 0.88 ps and at the cavity repetition rate of 5.47 MHz. Our results contribute to the growing body of work studying the nonlinear optical properties of ultrasmall PQDs that present new opportunities of this two-dimensional (2D) nanomaterial for future ultrafast photonic technologies.
153 citations
TL;DR: The authors show the first account of copper doping into atomically flat colloidal quantum wells (CQWs) that enables near-unity quantum efficiencies (up to ≈97%), accompanied by substantially high absorption cross-section and inherently step-like absorption profile, compared to those of the doped CQDs.
Abstract: Doping of bulk semiconductors has revealed widespread success in optoelectronic applications. In the past few decades, substantial effort has been engaged for doping at the nanoscale. Recently, doped colloidal quantum dots (CQDs) have been demonstrated to be promising materials for luminescent solar concentrators (LSCs) as they can be engineered for providing highly tunable and Stokes-shifted emission in the solar spectrum. However, existing doped CQDs that are aimed for full solar spectrum LSCs suffer from moderately low quantum efficiency, intrinsically small absorption cross-section, and gradually increasing absorption profiles coinciding with the emission spectrum, which together fundamentally limit their effective usage. Here, the authors show the first account of copper doping into atomically flat colloidal quantum wells (CQWs). In addition to Stokes-shifted and tunable dopant-induced photoluminescence emission, the copper doping into CQWs enables near-unity quantum efficiencies (up to ≈97%), accompanied by substantially high absorption cross-section and inherently step-like absorption profile, compared to those of the doped CQDs. Based on these exceptional properties, the authors have demonstrated by both experimental analysis and numerical modeling that these newly synthesized doped CQWs are excellent candidates for LSCs. These findings may open new directions for deployment of doped CQWs in LSCs for advanced solar light harvesting technologies.
130 citations
TL;DR: In this article, the authors identify arsenene oxide, AsO, as an excellent candidate, which demonstrates high stability, flexibility, and tunable spin-orbit coupling gaps, and propose a quantum well in which the band topology of AsO is preserved with a sizeable band gap.
Abstract: Searching for two-dimensional (2D) realistic materials that are able to realize room-temperature quantum spin Hall effects is currently a growing field. Here, through ab initio calculations, we identify arsenene oxide, AsO, as an excellent candidate, which demonstrates high stability, flexibility, and tunable spin-orbit coupling gaps. In contrast to known pristine or functionalized arsenene, the maximum nontrivial bandgap of AsO reaches 89 meV and can be further enhanced to 130 meV under biaxial strain. By sandwiching 2D AsO between boron nitride sheets, we propose a quantum well in which the band topology of AsO is preserved with a sizeable bandgap. Considering that AsO having fully oxidized surfaces are naturally stable against surface oxidization and degradation, this functionality provides a viable strategy for designing topological quantum devices operating at room temperature.
124 citations
TL;DR: The authors combine colloidal quantum wells with a photonic-crystal cavity into a stable, continuous-wave room-temperature nanolaser with a threshold below one microwatt, showing that colloidal nanocrystals are suitable for compact and efficient optoelectronic devices based on versatile and inexpensive solution-processable materials.
Abstract: Colloidal semiconductor nanocrystals have emerged as promising active materials for solution-processable optoelectronic and light-emitting devices. In particular, the development of nanocrystal lasers is currently experiencing rapid progress. However, these lasers require large pump powers, and realizing an efficient low-power nanocrystal laser has remained a difficult challenge. Here, we demonstrate a nanolaser using colloidal nanocrystals that exhibits a threshold input power of less than 1 μW, a very low threshold for any laser using colloidal emitters. We use CdSe/CdS core-shell nanoplatelets, which are efficient nanocrystal emitters with the electronic structure of quantum wells, coupled to a photonic-crystal nanobeam cavity that attains high coupling efficiencies. The device achieves stable continuous-wave lasing at room temperature, which is essential for many photonic and optoelectronic applications. Our results show that colloidal nanocrystals are suitable for compact and efficient optoelectronic devices based on versatile and inexpensive solution-processable materials. Colloidal nanocrystals are a promising material for easy-to-fabricate nanolasers, but suffer from high threshold powers. Here, the authors combine colloidal quantum wells with a photonic-crystal cavity into a stable, continuous-wave room-temperature nanolaser with a threshold below one microwatt
124 citations
TL;DR: In this paper, the authors proposed a quantum well in which the band topology of arsenene oxide is preserved with a sizeable band gap, which provides a viable strategy for designing topological quantum devices operating at room temperature.
Abstract: Searching for two-dimensional (2D) realistic materials able to realize room-temperature quantum spin Hall (QSH) effects is currently a growing field. Here, we through ab initio calculations to identify arsenene oxide, AsO, as an excellent candidate, which demonstrates high stability, flexibility, and tunable spin-orbit coupling (SOC) gaps. In contrast to known pristine or functionalized arsenene, the maximum nontrivial band gap of AsO reaches 89 meV, and can be further enhanced to 130 meV under biaxial strain. By sandwiching 2D AsO between BN sheets, we propose a quantum well in which the band topology of AsO is preserved with a sizeable band gap. Considering that AsO having fully oxidized surfaces are naturally stable against surface oxidization and degradation, this functionality provides a viable strategy for designing topological quantum devices operating at room temperature.
122 citations
TL;DR: In this article, the authors demonstrate highly efficient, low threshold InAs quantum dot lasers epitaxially grown on on on-axis (001) GaP/Si substrates using molecular beam epitaxy.
Abstract: We demonstrate highly efficient, low threshold InAs quantum dot lasers epitaxially grown on on-axis (001) GaP/Si substrates using molecular beam epitaxy Electron channeling contrast imaging measurements show a threading dislocation density of 73 × 106 cm−2 from an optimized GaAs template grown on GaP/Si The high-quality GaAs templates enable as-cleaved quantum dot lasers to achieve a room-temperature continuous-wave (CW) threshold current of 95 mA, a threshold current density as low as 132 A/cm2, a single-side output power of 175 mW, and a wall-plug-efficiency of 384% at room temperature As-cleaved QD lasers show ground-state CW lasing up to 80 °C The application of a 95% high-reflectivity coating on one laser facet results in a CW threshold current of 67 mA, which is a record-low value for any kind of Fabry-Perot laser grown on Si
117 citations
TL;DR: In this article, a measurement of multiple Andreev reflection (MAR) in a Josephson junction made from an InAs quantum well heterostructure with epitaxial aluminum is used to quantify a highly transparent effective semiconductor-superconductor interface with near-unity transmission.
Abstract: Measurement of multiple Andreev Reflection (MAR) in a Josephson junction made from an InAs quantum well heterostructure with epitaxial aluminum is used to quantify a highly transparent effective semiconductor-superconductor interface with near-unity transmission. The observed temperature dependence of MAR does not follow a conventional BCS form but instead agrees with a model in which the density of states in the quantum well acquires an effective induced gap, in our case, 180 μeV, close to that of the epitaxial superconductor, indicating an intimate contact between Al and the InAs heterostructure. The carrier density dependence of MAR is investigated using a depletion gate revealing the subband structure of the semiconductor quantum well, consistent with magnetotransport experiments of the bare InAs performed on the same wafer.
103 citations
TL;DR: In this paper, the authors introduced a method to account for quantum disorder effects into the classical drift-diffusion model of semiconductor transport through the localization landscape theory, which solved the carrier dynamics with quantum effects self-consistently and provided a computationally much faster solver when compared with the Schrodinger equation resolution.
Abstract: This paper introduces a novel method to account for quantum disorder effects into the classical drift-diffusion model of semiconductor transport through the localization landscape theory. Quantum confinement and quantum tunneling in the disordered system change dramatically the energy barriers acting on the perpendicular transport of heterostructures. In addition, they lead to percolative transport through paths of minimal energy in the two-dimensional (2D) landscape of disordered energies of multiple 2D quantum wells. This model solves the carrier dynamics with quantum effects self-consistently and provides a computationally much faster solver when compared with the Schr\"odinger equation resolution. The theory also provides a good approximation to the density of states for the disordered system over the full range of energies required to account for transport at room temperature. The current-voltage characteristics modeled by three-dimensional simulation of a full nitride-based light emitting diode (LED) structure with compositional material fluctuations closely match the experimental behavior of high-quality blue LEDs. The model allows also a fine analysis of the quantum effects involved in carrier transport through such complex heterostructures. Finally, details of carrier population and recombination in the different quantum wells are given.
101 citations
20 Feb 2017
TL;DR: In this paper, the authors report on advanced surface control of miniature gallium arsenide optical resonators using two distinct techniques that produce permanent results, extending the lifetime of free carriers and enhancing luminescence, while reducing surface absorption and enabling ultra-low optical dissipation devices.
Abstract: Gallium arsenide and related compound semiconductors lie at the heart of optoelectronics and integrated laser technologies. Shaped at the micro- and nanoscale, they allow strong interaction with quantum dots and quantum wells, and promise stunning optically active devices. However, gallium arsenide optical structures presently exhibit lower performance than their passive counterparts based on silicon, notably in nanophotonics, where the surface plays a chief role. Here, we report on advanced surface control of miniature gallium arsenide optical resonators using two distinct techniques that produce permanent results. One extends the lifetime of free carriers and enhances luminescence, while the other strongly reduces surface absorption and enables ultra-low optical dissipation devices. With such surface control, the quality factor of wavelength-sized optical disk resonators is observed to rise up to 6×106 at the telecom wavelength, greatly surpassing previous realizations and opening new prospects for gallium arsenide nanophotonics.
95 citations
TL;DR: In this paper, the performance of pulsed Er3+-and Ho3+doped ZBLAN (ZrF4-BaF2-LaF3-Al F3-NaF) fiber sources at 3 μm is presented.
Abstract: Enormous performance gains have been made in fluoride-based fiber lasers operating around 3 μm due to advances in fiber fabrication and improvements in high-power pump diode technologies during the last decade. Pulsed fluoride fiber lasers capable of producing high-energy/high-peak power mid-infrared pulses are of significant interest for a variety of applications. Q-switched and mode-locked fiber lasers have been demonstrated with various techniques in recent years. In this paper, pulsed Er3+- and Ho3+-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber lasers are reviewed, and our achievement of pulsed fiber laser sources at 3 μm is presented. Power/energy scaling of pulsed ZBLAN fiber lasers and their potential applications are discussed.
TL;DR: In this paper, a model of carrier distribution and transport in semiconductor alloys accounting for quantum localization effects in disordered materials is presented, which is based on the recent development of a mathematical theory of quantum localization which introduces a spatial function called localization landscape.
Abstract: We present here a model of carrier distribution and transport in semiconductor alloys accounting for quantum localization effects in disordered materials. This model is based on the recent development of a mathematical theory of quantum localization which introduces for each type of carrier a spatial function called localization landscape. These landscapes allow us to predict the localization regions of electron and hole quantum states, their corresponding energies, and the local densities of states. We show how the various outputs of these landscapes can be directly implemented into a drift-diffusion model of carrier transport and into the calculation of absorption/emission transitions. This creates a new computational model which accounts for disorder localization effects while also capturing two major effects of quantum mechanics, namely, the reduction of barrier height (tunneling effect) and the raising of energy ground states (quantum confinement effect), without having to solve the Schr\"odinger equation. Finally, this model is applied to several one-dimensional structures such as single quantum wells, ordered and disordered superlattices, or multiquantum wells, where comparisons with exact Schr\"odinger calculations demonstrate the excellent accuracy of the approximation provided by the landscape theory.
TL;DR: In this paper, the charge states in a double quantum dot (DQD) formed in a Si/SiGe heterostructure are read out using an on-chip superconducting microwave cavity.
Abstract: We demonstrate a hybrid device architecture where the charge states in a double quantum dot (DQD) formed in a Si/SiGe heterostructure are read out using an on-chip superconducting microwave cavity. A quality factor Q = 5400 is achieved by selectively etching away regions of the quantum well and by reducing photon losses through low-pass filtering of the gate bias lines. Homodyne measurements of the cavity transmission reveal DQD charge stability diagrams and a charge-cavity coupling rate g c / 2 π = 23 MHz. These measurements indicate that electrons trapped in a Si DQD can be effectively coupled to microwave photons, potentially enabling coherent electron-photon interactions in silicon.
20 Feb 2017
TL;DR: In this article, the authors compare multi-quantum-well (MQW) light-emitting diodes (LEDs) with Ge0.915Sn0.085 wells and Si0.1Ge0.8Sn 0.1 barriers.
Abstract: Group IV photonics is on its way to be integrated with electronic circuits, making information transfer and processing faster and more energy efficient. Light sources, a critical component of photonic integrated circuits, are still in development. Here, we compare multi-quantum-well (MQW) light-emitting diodes (LEDs) with Ge0.915Sn0.085 wells and Si0.1Ge0.8Sn0.1 barriers to a reference Ge0.915Sn0.085 homojunction LED. Material properties as well as band structure calculations are discussed, followed by optical investigations. Electroluminescence spectra acquired at various temperatures indicate effective carrier confinement for electrons and holes in the GeSn quantum wells and confirm the excellent performance of GeSn/SiGeSn MQW light emitters.
TL;DR: In this paper, a three-dimensional absorption model is developed based on disorder-induced localization which provides the effective potential seen by the localized carriers without having to resort to the solution of the Schrodinger equation in a disordered potential.
Abstract: Urbach tails in semiconductors are often associated to effects of compositional disorder. The Urbach tail observed in InGaN alloy quantum wells of solar cells and LEDs by biased photocurrent spectroscopy is shown to be characteristic of the ternary alloy disorder. The broadening of the absorption edge observed for quantum wells emitting from violet to green (indium content ranging from 0% to 28%) corresponds to a typical Urbach energy of 20 meV. A three-dimensional absorption model is developed based on a recent theory of disorder-induced localization which provides the effective potential seen by the localized carriers without having to resort to the solution of the Schr\"odinger equation in a disordered potential. This model incorporating compositional disorder accounts well for the experimental broadening of the Urbach tail of the absorption edge. For energies below the Urbach tail of the InGaN quantum wells, type-II well-to-barrier transitions are observed and modeled. This contribution to the below-band-gap absorption is particularly efficient in near-ultraviolet emitting quantum wells. When reverse biasing the device, the well-to-barrier below-band-gap absorption exhibits a red-shift, while the Urbach tail corresponding to the absorption within the quantum wells is blue-shifted, due to the partial compensation of the internal piezoelectric fields by the external bias. The good agreement between the measured Urbach tail and its modeling by the localization theory demonstrates the applicability of the latter to compositional disorder effects in nitride semiconductors.
20 Dec 2017
TL;DR: In this paper, the aspect ratio defect trapping technique was used to trap unwanted defects in the silicon substrate and grow high-quality nano-rigid laser structures on a standard 300mm Si wafer.
Abstract: Fully exploiting the potential of silicon photonics requires high-performance active devices such as lasers, which can be monolithically integrated in a scalable way. However, direct bandgap III–V semiconductors exhibit a large lattice mismatch and/or strongly differing thermal expansion coefficient with silicon. This makes monolithic integration on silicon without introducing excessive defects in the material extremely difficult. The majority of the methods proposed thus far either are not compatible with further low-cost integration or rely on a special substrate. Here we demonstrate monolithic InGaAs/GaAs single-mode nano-ridge lasers directly grown on a standard (001) 300-mm Si wafer. Exploiting the aspect ratio defect trapping technique, unwanted defects are confined to a narrow trench defined in the silicon substrate. The nano-ridge structures subsequently grown out of these trenches are of high crystalline quality as shown by high-resolution transmission electron microscopy analysis and a strong photoluminescence response. They can be controlled in shape by optimizing the growth conditions, which allows us to minimize substrate leakage and maximize confinement in the InGaAs quantum wells providing optical gain. Distributed feedback lasers were fabricated by defining a first-order grating in the nano-ridge. Under pulsed optical pumping, single-mode lasing with side mode suppression over 28 dB was shown, and precise control of the emission wavelength over 60 nm was achieved. This demonstration proves the high quality of the material and provides a credible road towards a CMOS-compatible platform for high-volume manufacturing of silicon photonic integrated circuits, including laser and amplifier devices.
TL;DR: It is found that interchannel scattering between same-spin edge channels along the physical graphene edge can be used to form beamsplitters, whereas the absence of inter channel scattering along gate-defined interfaces can beused to form isolated interferometer arms.
Abstract: Confined to a two-dimensional plane, electrons in a strong magnetic field travel along the edge in one-dimensional quantum Hall channels that are protected against backscattering. These channels can be used as solid-state analogs of monochromatic beams of light, providing a unique platform for studying electron interference. Electron interferometry is regarded as one of the most promising routes for studying fractional and non-Abelian statistics and quantum entanglement via two-particle interference. However, creating an edge-channel interferometer in which electron-electron interactions play an important role requires a clean system and long phase coherence lengths. We realize electronic Mach-Zehnder interferometers with record visibilities of up to 98% using spin- and valley-polarized edge channels that copropagate along a pn junction in graphene. We find that interchannel scattering between same-spin edge channels along the physical graphene edge can be used to form beamsplitters, whereas the absence of interchannel scattering along gate-defined interfaces can be used to form isolated interferometer arms. Surprisingly, our interferometer is robust to dephasing effects at energies an order of magnitude larger than those observed in pioneering experiments on GaAs/AlGaAs quantum wells. Our results shed light on the nature of edge-channel equilibration and open up new possibilities for studying exotic electron statistics and quantum phenomena.
TL;DR: The realization of high-quality GaN QDs will enable exploration of optoelectronic properties of III-nitrides, opening up the possibility of realizing single-photon quantum information systems operating at room temperature.
Abstract: Wide bandgap III-nitride quantum dots (QDs) are promising materials for the realization of solid-state single-photon sources, especially operating at room temperature. However, so far a large degree of inhomogeneous broadening induced by spectral diffusion has compromised their use. Here, we demonstrate the ultraclean emission from single GaN QDs formed at macrostep edges in a GaN/AlGaN quantum well. As a likely consequence of the high growth temperature and hence a reduced defect density, spectral diffusion is heavily suppressed to levels at least 1 order of magnitude lower than conventional GaN QDs. A record narrow line width of as small as 87 μeV is obtained, while the low inhomogeneous broadening enables us to assess an upper limit of homogeneous broadening in the QDs (27 μeV). Furthermore, the uncontaminated emission facilitates the generation of ultraviolet single-photons with unprecedented purity (g(2)(0) = 0.02). The realization of high-quality GaN QDs will enable exploration of optoelectronic pro...
TL;DR: This work demonstrates luminescent hyperbolic metasurfaces, wherein distributed semiconducting quantum wells display extreme absorption and emission polarization anisotropy and experimentally demonstrates >350% emission intensity enhancement relative to the bare semiconducted quantum wells.
Abstract: When engineered on scales much smaller than the operating wavelength, metal-semiconductor nanostructures exhibit properties unobtainable in nature. Namely, a uniaxial optical metamaterial described by a hyperbolic dispersion relation can simultaneously behave as a reflective metal and an absorptive or emissive semiconductor for electromagnetic waves with orthogonal linear polarization states. Using an unconventional multilayer architecture, we demonstrate luminescent hyperbolic metasurfaces, wherein distributed semiconducting quantum wells display extreme absorption and emission polarization anisotropy. Through normally incident micro-photoluminescence measurements, we observe absorption anisotropies greater than a factor of 10 and degree-of-linear polarization of emission >0.9. We observe the modification of emission spectra and, by incorporating wavelength-scale gratings, show a controlled reduction of polarization anisotropy. We verify hyperbolic dispersion with numerical simulations that model the metasurface as a composite nanoscale structure and according to the effective medium approximation. Finally, we experimentally demonstrate >350% emission intensity enhancement relative to the bare semiconducting quantum wells.
TL;DR: In this paper, the evolution of QDs, as well as improved device performances for novel application fields are discussed, where the authors discuss the use of QD lasers for resource searching by utilizing high-temperature operation such as lasing at higher than 200°C.
Abstract: The device characteristics of semiconductor lasers have been improved with progress in active layer structures. Carrier confinement dimension plays an important role especially in temperature sensitivity as well as slope efficiency. Three-dimensional carrier confinement to nano-scale semiconductor crystal, known as “quantum dots (QDs)” had been predicted to show ultimately superior device performances. Self-assembly formed InAs QDs grown on GaAs had been intensively promoted in order to achieve QD lasers with superior device performances. Now high-density, high-optical quality QDs have been realized through improved molecular beam epitaxy growths and QD lasers with better temperature characteristics are in the stage of mass-production for a data-com market. Fabry–Perot type, as well as distributed feedback type QD lasers show quite improved laser characteristics. Also, the unique device characteristics of QD lasers opened new application fields such as the use for resource searching by utilizing high-temperature operation such as lasing at higher than 200 °C. For silicon-photonics, QD lasers are used as an optical source for athermal operation. In this paper, the evolution of QDs, as well as improved device performances for novel application fields are discussed.
TL;DR: Band structure analysis of the pseudomorphic GeSn/Ge quantum well structures indicated that, despite the stronger quantum confinement, the absorption edge can be shifted to longer wavelengths by increasing the Sn content, thereby enabling efficient photodetection in the infrared region.
Abstract: We report on Sn-based p-i-n waveguide photodetectors (WGPD) with a pseudomorphic GeSn/Ge multiple-quantum-well (MQW) active layer on a Ge-buffered Si substrate. A reduced dark-current density of 59 mA/cm2 was obtained at a reverse bias of 1 V due to the suppressed strain relaxation in the GeSn/Ge active layer. Responsivity experiments revealed an extended photodetection range covering the O, E, S, C, and L telecommunication bands completely due to the bandgap reduction resulting from Sn-alloying. Band structure analysis of the pseudomorphic GeSn/Ge quantum well structures indicated that, despite the stronger quantum confinement, the absorption edge can be shifted to longer wavelengths by increasing the Sn content, thereby enabling efficient photodetection in the infrared region. These results demonstrate the feasibility of using GeSn/Ge MQW planar photodetectors as building blocks of electronic-photonic integrated circuits for telecommunication and optical interconnection applications.
TL;DR: This work reports aggregation-induced emission phenomena in lamellar solids containing layer-controlled colloidal quantum wells of hybrid organic-inorganic lead bromide perovskites, resulting in anomalously high solid-state ηPL, the first low-dimensional semiconductor nanocrystal system that increases the photoluminescence quantum yield in aggregates.
Abstract: The outstanding excitonic properties, including photoluminescence quantum yield (ηPL), of individual, quantum-confined semiconductor nanoparticles are often significantly quenched upon aggregation, representing the main obstacle toward scalable photonic devices. We report aggregation-induced emission phenomena in lamellar solids containing layer-controlled colloidal quantum wells (QWs) of hybrid organic-inorganic lead bromide perovskites, resulting in anomalously high solid-state ηPL of up to 94%. Upon forming the QW solids, we observe an inverse correlation between exciton lifetime and ηPL, distinct from that in typical quantum dot solid systems. Our multiscale theoretical analysis reveals that, in a lamellar solid, the collective motion of the surface organic cations is more restricted to orient along the [100] direction, thereby inducing a more direct bandgap that facilitates radiative recombination. Using the QW solids, we demonstrate ultrapure green emission by completely downconverting a blue gallium nitride light-emitting diode at room temperature, with a luminous efficacy higher than 90 lumen W-1 at 5000 cd m-2, which has never been reached in any nanomaterial assemblies by far.
TL;DR: A state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (β-Ga2O3) substrate is demonstrated using a straightforward growth process that does not require a high-cost lift-off technique or complex fabrication process, which is cost-effective for large-scale devices.
Abstract: We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (−201)-oriented (β-Ga2O3) substrate, obtained using a straightforward growth process that does not require a high-cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multiquantum well (MQW) grown on the masked β-Ga2O3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ∼86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low tem...
TL;DR: In this article, the authors report on stimulated emission at wavelengths up to 19.5μm from HgTe/HgCdTe quantum well heterostructures with wide gap HgCDTe dielectric waveguide, grown by molecular beam epitaxy on GaAs(013) substrates.
Abstract: We report on stimulated emission at wavelengths up to 19.5 μm from HgTe/HgCdTe quantum well heterostructures with wide‐gap HgCdTe dielectric waveguide, grown by molecular beam epitaxy on GaAs(013) substrates. The mitigation of Auger processes in structures under study is exemplified, and the promising routes towards the 20–50 μm wavelength range, where HgCdTe lasers may be competitive to the prominent emitters, are discussed.
TL;DR: In this article, the energy, effective Bohr radius, and radiative lifetime of neutral excitons confined in CdSe colloidal nanoplatelets (NPLs) are calculated using semianalytical models.
Abstract: Using semianalytical models we calculate the energy, effective Bohr radius, and radiative lifetime of neutral excitons confined in CdSe colloidal nanoplatelets (NPLs). The excitonic properties are largely governed by the electron-hole in-plane correlation, which in NPLs is enhanced by the quasi-two-dimensional motion and the dielectric mismatch with the organic environment. In NPLs with lateral size $L\ensuremath{\gtrsim}20$ nm the exciton behavior is essentially that in a quantum well, with super-radiance leading to exciton lifetimes of 1 ps or less, only limited by the NPL area. However, for $Ll20$ nm excitons enter an intermediate confinement regime, hence departing from the quantum well behavior. In heterostructured NPLs, a different response is observed for core-shell and core-crown configurations. In the former, the strong vertical confinement limits separation of electrons and holes even for type-II band alignment. The exciton behavior is then similar to that in core-only NPL, albeit with weakened dielectric effects. In the latter, charge separation is also inefficient if band alignment is quasi-type-II (e.g., in CdSe/CdS), because electron-hole interaction drives both carriers into the core. However, it becomes very efficient for type-II alignment, for which we predict exciton lifetimes reaching microseconds.
TL;DR: This represents the shortest pulses in Q-switched MIR lasers based on a 2D material as the saturable absorber, which demonstrated the superiority of ReS2 acting as an optical modulator for generating short-pulsed lasers.
Abstract: A novel two-dimensional (2D) material member in the transition metal dichalcogenides family, few-layered rhenium disulfide (ReS2) was prepared by liquid phase method successfully. By using the open-aperture Z-scan method, the saturable absorption properties at 2.8 μm were characterized with a saturable fluence of 22.6 μJ/cm2 and a modulation depth of 9.7%. A passively Q-switched solid-state laser at 2.8 μm was demonstrated by using the as-prepared ReS2 saturable absorber successfully. Under an absorbed pump power of 920 mW, a maximum output power of 104 mW was obtained with a pulse width of 324 ns and a repetition rate of 126 kHz. To the best of our knowledge, this is the first demonstration of applying ReS2 in an all-solid-state laser. Moreover, this represents the shortest pulses in Q-switched MIR lasers based on a 2D material as the saturable absorber, which demonstrated the superiority of ReS2 acting as an optical modulator for generating short-pulsed lasers. The results well prove that 2D ReS2 is a reliable optical modulator for MIR solid-state lasers.
TL;DR: In this article, it was shown that high-quality epitaxial ultrathin binary GaN quantum disks embedded in an AlN matrix can produce efficient optical emission in the 219-235 nm (∼5.7-5.3
Abstract: Deep ultraviolet (UV) optical emission below 250 nm (∼5 eV) in semiconductors is traditionally obtained from high aluminum containing AlGaN alloy quantum wells. It is shown here that high-quality epitaxial ultrathin binary GaN quantum disks embedded in an AlN matrix can produce efficient optical emission in the 219–235 nm (∼5.7–5.3 eV) spectral range, far above the bulk bandgap (3.4 eV) of GaN. The quantum confinement energy in these heterostructures is larger than the bandgaps of traditional semiconductors, made possible by the large band offsets. These molecular beam epitaxy-grown extreme quantum-confinement GaN/AlN heterostructures exhibit an internal quantum efficiency of 40% at wavelengths as short as 219 nm. These observations together with the ability to engineer the interband optical matrix elements to control the direction of photon emission in such binary quantum disk active regions offer unique advantages over alloy AlGaN quantum well counterparts for the realization of deep-UV light-emitting d...
TL;DR: In this paper, the polarization properties of molecular beam epitaxy-grown AlN/GaN QW-like UV LEDs, which consist of 3-4 monolayer (QW)-like) delta-GaN layers sandwiched by 2.5-nm AlN sub-QW layers, are investigated.
Abstract: This work investigates the physics and polarization characteristics of 298 nm AlN-delta-GaN quantum well (QW) ultraviolet (UV) light-emitting diodes (LEDs). The physics analysis shows that the use of the AlN-delta-GaN QW structure can ensure dominant conduction band (C) to heavy-hole (HH) subband transition and significantly improve the electron and top HH subband wave function overlap. As a result, up to 30-times enhancement in the transverse-electric (TE)-polarized spontaneous emission rate of the proposed structure can be obtained as compared to a conventional AlGaN QW structure. The polarization properties of molecular beam epitaxy-grown AlN/GaN QW-like UV LEDs, which consist of 3–4 monolayer (QW-like) delta-GaN layers sandwiched by 2.5-nm AlN sub-QW layers, are investigated in this study. The polarization-dependent electroluminescence measurement results are consistent with the theoretical analysis. Specifically, the TE-polarized emission intensity is measured to be much larger than the transverse-ma...
TL;DR: In this paper, a series of GaAsBi/GaAs multiple quantum well diodes were compared with InGaAs based devices to assess the potential of GAsBi for photovoltaic applications.
Journal Article•
TL;DR: High-resolution angle-resolved photoelectron spectroscopy measurements systematically on 14-202 bilayer Bi films prove the fundamental property of Bi and introduce a capability of the quantum-confinement approach.
Abstract: Characterization of the nontrivial topology in bismuth through high-resolution ARPES measurements is aided by a new quantum well geometry.