A single microwire near-infrared exciton-polariton light-emitting diode

Plasmonically-boosted exciton-photon coupling strength in a near-infrared LED based on a ZnO:Ga microwire/GaAs heterojunction with surface-coated Au&Ag alloy nanorods

The development of electrically-driven low-dimensional coherent light sources via highly-polarized polariton emission behavior has been extensively researched, but suffers from limited modulation of the exciton-photon coupling strengths. Herein, an electrically-biased near-infrared exciton-polariton light-emitting diode (LED), which includes a Ga-doped ZnO microwire (ZnO:Ga MW) and p-type GaAs substrate, is demonstrated. The well-designed LED structure is conducive to producing strong coupling between excitons and cavity photons, thus yielding highly-polarized light-emissions due to the optical birefringence in the ZnO:Ga MW microcavity. In particular, when the LED device is modified using Au&Ag alloy nanorods (AuAgNRs) with desired plasmonic properties, the electroluminescence (EL) performance is significantly boosted, especially the Rabi-splitting energy, which increases from 96 to 285 meV. The current-injection exciton-polariton emission from the LED undergoing a strong coupling regime is confirmed through angle-resolved EL measurements. This study exhibits a performance-boosted near-infrared exciton-polariton LED at room temperature, which provides a new scheme toward the realization of highly energy-efficient polariton coherent light sources. Further, the significantly lower density of polariton states induced by the incorporated metal nanostructures highlights a bright future of realizing ultralow-threshold polariton lasers much more feasibly, in comparison to conventional lasers based on narrow bandgap semiconductors.

Highly Monochromatic Ultraviolet LED Based on the SnO2 Microwire Heterojunction Beyond Dipole-Forbidden Band-Gap Transition

SnO2 has been extensively applied in the fields of optoelectronic devices because of its large band gap, high exciton binding energy, and outstanding optical/electrical properties. However, its applications in ultraviolet light-emitting diodes (LEDs) are still hindered by the dipole-forbidden rule. Herein, the dipole-forbidden rule can be conquered by synthesizing Sb-incorporated SnO2 microwires (SnO2:Sb MWs), which are examined by ultraviolet photoluminescence emitting at 363.2 nm and a line width of 11.3 nm. Subsequently, a highly monochromatic ultraviolet light-emitting diode (LED) based on a SnO2:Sb MW heterojunction was constructed with a p-GaN film serving as the hole supplier. In the LED, the presence of a MgO intermediate layer can modulate carrier transport and recombination path, thus achieving band-edge optical transition in the SnO2:Sb MW. As the LED is modified using Ag nanowires, electrical properties, especially for the hole injection efficiency, were dramatically boosted, contributing significantly to the device high brightness. The LED emits at 365.9 nm and a line width of 12.4 nm. Therefore, we have realized a high-brightness and narrow-band ultraviolet LED with the shortest peak wavelength never seen in previously reported SnO2 LEDs. This work will promote the potential applications of low-dimensional SnO2 optoelectronic devices and provide an effective exemplification to overcome the dipole-forbidden rule in metal-oxide materials with "forbidden" energy gaps.

Exciton-polariton light-emitting diode based on a single ZnO superlattice microwire heterojunction with performance enhanced by Rh nanostructures

One-dimensional (1D) wirelike superlattice micro/nanostructures have received considerable attention for potential applications due to their versatility and capability for modulating optical and electrical characteristics. In this study, 1D superlattice microwires (MWs), which are made of undoped ZnO and Ga-doped ZnO with periodic and alternating crystalline layers (ZnO/ZnO:Ga), were synthesized individually. Under optical excitation, a series of resonance peaks in the photoluminescence spectrum can be ascribed to polariton emission, which originates from the coupling interaction of the 1D photonic crystal and confined excitons along the wire direction. Using a p-type GaN layer as the hole transport layer, a kind of waveguide light source based on an individual ZnO/ZnO:Ga superlattice MW was proposed and constructed. By analysing the spatially resolved electroluminescence spectra, the observed multipeak was ascribed to exciton-polariton emission with a vacuum Rabi splitting of about 275 meV. Cladding with Rh nanostructures gives rise to appropriate ultraviolet plasmons, and the Rabi splitting energy of our device was enhanced up to 413 meV. The exciton-polariton properties were further examined using angle-resolved electroluminescence measurements. Therefore, individual superlattice MWs can act as optical microresonators to achieve photon-exciton coupling with a large Rabi splitting energy. The experimental results indicate that an individual ZnO/ZnO:Ga superlattice MW can be generally used in developing exciton-polariton luminescence/lasing light sources, particularly for constructing low-threshold/thresholdless lasers toward pragmatic applications.

Interface engineering enhanced near-infrared electroluminescence in an n-ZnO microwire/p-GaAs heterojunction

Interface engineering in the fabrication of low-dimensional optoelectronic devices has been highlighted in recent decades to enhance device characteristics such as reducing leakage current, optimizing charge transport, and modulating the energy-band structure. In this paper, we report a dielectric interface approach to realize one-dimensional (1D) wire near-infrared light-emitting devices with high brightness and enhanced emission efficiency. The light-emitting diode is composed of a zinc oxide microwire covered by a silver nanolayer (Ag@ZnO MW), magnesium oxide (MgO) buffer layer, and p-type gallium arsenide (GaAs) substrate. In the device structure, the insertion of a MgO dielectric layer in the n-ZnO MW/p-GaAs heterojunction can be used to modulate the device features, such as changing the charge transport properties, reducing the leakage current and engineering the band alignment. Furthermore, the cladding of the Ag nanolayer on the ZnO MW can optimize the junction interface quality, thus reducing the turn-on voltage and increasing the current injection and electroluminescence (EL) efficiency. The combination of MgO buffer layer and Ag nanolayer cladding can be utilized to achieve modulating the carrier recombination path, interfacial engineering of heterojunction with optimized band alignment and electronic structure in these carefully designed emission devices. Besides, the enhanced near-infrared EL and improved physical contact were also obtained. The study of current transport modulation and energy-band engineering proposes an original and efficient route for improving the device performances of 1D wire-type heterojunction light sources.

Two-round quasi-whispering gallery mode exciton polaritons with large Rabi splitting in a GaN microrod

We investigate the exciton polaritons and their corresponding optical modes in a hexagonal GaN microrod at room temperature. The dispersion curves are measured by the angle-resolved micro-photoluminescence spectrometer, and two types of exciton polaritons are identified with the help of the finite-difference time-domain simulation. By changing the pump position, the photon part of the exciton polaritons is found to switch between the quasi-whispering gallery modes and the two-round quasi-whispering gallery modes. The exciton polaritons formed by the latter are observed and distinguished for the first time, with a giant Rabi splitting as large as 2Ω = 230.3 meV.

Self-powered ultraviolet photodetector based on an n-ZnO:Ga microwire/p-Si heterojunction with the performance enhanced by a pyro-phototronic effect

In the present study, a heterojunction made of an individual ZnO microwire via Ga incorporation (ZnO:Ga MW) with a p-Si substrate was constructed to develop a self-powered ultraviolet photodetector. When operated under an illumination of 370 nm light with a power density of ∼ 0.5 mW/cm², the device exhibited an excellent responsivity of 0.185 A/W, a large detectivity of 1.75×10¹² Jones, and excellent stability and repeatability. The device also exhibited a high on/off photocurrent ratio up to 10³, and a short rising and falling time of 499/412 μs. By integrating the pyro-phototronic effect, the maximum responsivity and detectivity increased significantly to 0.25 A/W and 2.30×10¹² Jones, respectively. The response/recovery time was drastically reduced to 79/132 μs without an external power source. In addition, the effects of light wavelength, power density, and bias voltage on the photocurrent response mediated by the pyro-phototronic effect were systematically characterized and discussed. Our work not only provides an easy yet efficient procedure for constructing a self-powered ultraviolet photodetector but also broadens the application prospects for developing individual wire optoelectronic devices based on the photovoltaic-pyro-phototronic effect.

Mapping of Fabry-Perot and whispering gallery modes in GaN microwires by nonlinear imaging

Engineering nonlinear optical responses at the microscale is a key topic in photonics for achieving efficient frequency conversion and light manipulation. Gallium nitride (GaN) is a promising semiconductor material for integrated nonlinear photonic structures. In this work, we use epitaxially grown GaN microwires as nonlinear optical whispering gallery and Fabry-Perot resonators. We demonstrate an effective generation of second-harmonic and polarization-dependent signals of whispering gallery and Fabry-Perot modes (FPM) under near-infrared (NIR) excitation. We show how the rotation of the excitation polarization can be used to control and switch between Fabry-Perot and whispering gallery modes in tapered GaN microwire resonators. We demonstrate the enhancement of two-photon luminescence in the yellow-green spectral range due to efficient coupling between whispering gallery, FPM, and excitonic states in GaN. This luminescence enhancement allows us to conveniently visualize whispering gallery modes excited with a NIR source. Such microwire resonators can be used as compact microlasers or sensing elements in photonic sensors.

An electrically driven whispering gallery polariton microlaser

Near-infrared micro/nanolaser devices utilizing low-dimensional semiconductors can provide essential building blocks to achieve integrated optoelectronic devices and circuitry for advanced functionalities and are compatible with on-chip technologies. Although significant progress has been made through using narrow-band semiconductor micro/nanostructures to realize near-infrared stimulated radiation at room temperature, severe challenges still remain involving much lower quantum efficiencies and higher auger recombination. Herein, we report an experimental realization of a current-injection semiconductor polariton device made of a ZnO microwire via Ga-doping (ZnO:Ga MW) and p-type GaAs template. The device can emit polaritonic illumination directly from sharp edges of the hexagonal MW. The experimental results of angle-resolved electroluminescence measurements reveal a typical anticrossing feature between excitons and cavity modes, unambiguous evidence of the strong exciton-polariton coupling, with corresponding Rabi splitting energy extracted to be about 195 meV. As the applied bias goes above a certain value, electrically driven whispering gallery lasing action was achieved in the near-infrared spectrum, and the lasing features can be assigned to the exciton-polariton effect. The results not only can afford insights into the development of low-threshold coherent light sources via the exciton-polariton effect, but also can expand the fabrication of low-dimensional, near-infrared microlaser devices.

An electrically driven single microribbon based near-infrared exciton–polariton light-emitting diode

An electrically driven exciton–polariton NIR-LED involving an n-ZnO:Ga microribbon/p-GaAs heterojunction was achieved. The Rabi splitting is measured to be 109 meV.