In this report, we successfully fabricate a high-temporal-response β-Ga2O3/GaN heterojunction ultraviolet photodetector. A high-quality 2-inch single-crystalline β-Ga2O3 film is grown on GaN template with a GaOx buffer layer using Plasma-Assisted Molecule Beam Epitaxy (PA-MBE). Based on the as-grown film, a self-powered heterojunction detector with a unilateral recessed interdigital electrode is constructed. The device exhibits a broad-spectrum ultraviolet selective response characteristics with a cut-off edge at 330 nm and achieves a responsivity of 0.7 A/W under zero bias. Under a bias of 5 V, the rapid photoresponse rise time and decay time are 30 μs and 10.8 ms, respectively, and the photo-to-dark current ratio (PDCR) reaches 103. Considering the heterojunction energy band structure of β-Ga2O3/GaN, the work function difference of 0.43 eV facilitates electron migration and enables the self-powered operation. These results demonstrate a promising and efficient approach for developing high-performance, self-powered UV photodetectors and offer a robust alternative to conventional high-energy-consuming UV detection systems.

Nonlinear parametric process plays a pivotal role in modern optoelectronics, underpinning the central role in optical amplification, quantum networks as well as entangled photon pair generation. Compared to pure photonic systems constrained by weak polarizability and stringent phase-matching conditions, exciton-polaritons sustain parametric scattering at significantly lower thresholds due to their strong polariton-polariton interactions. Although polariton parametric scattering (PPS) has been reported, the deterministic generation of quantum-correlated photon pairs remains a challenge. Here, entangled photon pair is demonstrated that generated via nonlinear PPS in microcavity, where strong coupled hybrid polaritons with three anti-crossing eigenstates provide ideal scattering channels for PPS. The far-field patterns demonstrate macroscopic polariton occupation of signal- and idler-states, signifying the transition from Rayleigh scattering to nonlinear parametric scattering regime. Additionally, polarization and second-order temporal correlation measurements reveal orthogonal polarization properties and quantum correlations, highlighting the potential for entangled photon pair generation. Theoretical simulations using coupled Gross-Pitaevskii equations explore the dynamics with high fidelity. These results establish a platform for on-demand entangled photon generation, advancing quantum polaritonics toward practical applications in quantum communication and information processing.

Colloidal quantum dots (CQDs) are excellent optical gain media that can be synthesized through low-cost and easily controlled techniques, holding significant promise for applications in semiconductor laser devices. In this study, we demonstrated polariton coherent lasing based on a CdSe-based CQD microcavity device at room-temperature (RT) for the first time. The dispersion behaviors of CQD polaritons with different excitation powers were comprehensively analyzed using angle-resolved spectroscopy techniques. The lasing behavior at a threshold of 49 μJ cm-2 and the energy blue-shift were well aligned with the typical characteristics of robust polariton Bose-Einstein condensation (BEC) theory. Moreover, the linewidth of the polariton lasing peak was narrowed down to 0.65 nm at 1.13Pth. Additionally, the polarization characteristics and temporal dynamics of the CQD-microcavity polariton lasing were discussed. It was noted that the lifetime of CQD polaritons during condensation was reduced from 1.3 ns (0.8Pth) to 68 ps (1.6Pth). Our results provide valuable insights into the strong coupling, low-threshold CQD microcavity laser at RT and promote its further practical application.

Exciton-polaritons, hybrid states composed of excitons and photons under strong coupling, play a crucial role in investigating Bose-Einstein condensation (BEC) and optoelectronics. However, the relaxation bottleneck in exciton-polaritons, arising from reduced scattering efficiency with acoustic phonons, hinders the achievement of thermal equilibrium Bose-Einstein condensation (BEC). Here, by invoking the polaronic effect of the exciton, we present the first observation of polaron-polariton BEC in a GaN-based microcavity. The dispersion pattern in k-space reveals a typical middle polariton (MP) branch of polaron-polaritons. This unique dispersion structure enables a novel relaxation route through LO-phonon-mediated scattering for polaron-polaritons, overcoming the phonon bottleneck observed in exciton-polaritons. By utilizing this mechanism, we achieve a robust polaron-polariton BEC, which is confirmed by the characteristics of massive occupation of the ground state, linear polarization buildup, and long-range spatial coherence. Our findings provide new insights into thermal equilibrium BEC and high-performance polariton quantum devices with GaN materials.

With the development of ultra-fast optical technology, the nonlinear interaction between light and matter has attracted great attention. Upconversion laser generation through multiphoton absorption (MPA) enables numerous critical applications such as quantum signal processing, biophotonics, and 3D microfabrication. Herein, an ultra-low threshold single-mode four-photon absorption (4PA) upconversion lasing at room-temperature (RT) by constructing a strong-coupling microcavity is demonstrated. The planar microcavity significantly enhances the 4PA nonlinear interaction, which facilitates the obtainment of low-threshold upconversion lasing with an excellent output divergence angle and beam quality. In addition, the temporal dynamic mechanism and polarization characteristics of single-mode upconversion lasing are also comprehensively discussed. The work provides a feasible approach to fabricate a low-threshold single-mode upconversion laser through high-order nonlinear MPA processes.

Exciton-polaritons, hybrid quasiparticles from the strong coupling of excitons and cavity photons in semiconductor microcavities, offer a platform for exploring quantum coherence and nonlinear optical properties. The unique polariton parametric scattering (PPS) laser is of interest for its potential in quantum technologies and nonlinear devices. However, direct resonant excitation of polaritons in strong-coupling microcavities is challenging. This study proposes an innovative two-photon absorption (TPA) pump mechanism to address this. We observe TPA-driven PPS lasing in a strongly coupled microcavity at room temperature. High K-value exciton injections promote coherent stimulated emission of polariton scattering through intermode channels. Angle-resolved spectra confirm a TPA process, showing evolution from pump-state to signal-state. Hanbury Brown-Twiss measurement of second-order correlation g(2)(tau) of signal state indicates a phase transition from a classical thermal state to a quantum coherent state. Theoretical modeling provides insights into the physical mechanisms of PPS. Our work advances nonlinear phenomena exploration in strongly coupled light-matter systems, contributing to quantum polaritonics and nonlinear optics.

Exciton–polaritons, which are bosonic quasiparticles with an extremely low mass, play a key role in understanding macroscopic quantum effects related to Bose–Einstein condensation (BEC) in solid-state systems. The study of trapped polaritons in a potential well provides an ideal platform for manipulating polariton condensates, enabling polariton lasing with specific formation in k-space. Here, we realize quantized microcavity polariton lasing in simple harmonic oscillator (SHO) states based on spatial localized excitons in InGaN/GaN quantum wells (QWs). Benefiting from the high exciton binding energy (90 meV) and large oscillator strength of the localized exciton, room-temperature (RT) polaritons with large Rabi splitting (61 meV) are obtained in a strongly coupled microcavity. The manipulation of polariton condensates is performed through a parabolic potential well created by optical pump control. Under the confinement situation, trapped polaritons are controlled to be distributed in the selected quantized energy sublevels of the SHO state. The maximum energy spacing of 11.3 meV is observed in the SHO sublevels, indicating the robust polariton trapping of the parabolic potential well. Coherent quantized polariton lasing is achieved in the ground state of the SHO state and the coherence property of the lasing is analyzed through the measurements of spatial interference patterns and g(2)(τ). Our results offer a feasible route to explore the manipulation of macroscopic quantum coherent states and to fabricate novel polariton devices towards room-temperature operations.

Polariton lasing via Bose-Einstein condensation (BEC) provides a peculiar method to achieve low threshold coherent light sources. Until now, the cryogenic operating temperature required for polariton lasers has hampered the development of polaritonics. Here, a novel approach is first reported to realize the ultra-narrow linewidth polariton lasing under quasi-3D quantum confinement at room-temperature (RT). The potential trap landscape is constructed by ring-shaped optical excitation, wherein the continuum polariton dispersion is modulated into discrete simple harmonic oscillator (SHO) states. The coherent condensation lasing of trapped polaritons occurs beyond the threshold power. Benefiting from the horizontal quantum confinement, the trapped polariton lasing exhibits an ultra-narrow linewidth (0.7 meV) and excellent quality factor (Q = 3510). Moreover, the second-order quantum coherence properties of trapped polariton condensation are determined to reveal the quantum phase transition of Bosonic system. The results offer a feasible route for realizing a low-threshold ultra-narrow linewidth polariton laser at RT, which significantly facilitates the fabrication of polariton laser and switches on opportunities for future applications. A SLM is utilized to modulate the excitation into a ring-shaped beam, which will form a horizontal potential trap in the active region of the microcavity. Free polaritons that are created on the ring will then drop into the trap and redistribute in both energy and space as quantized SHO states. As the excitation power is raised, polaritons will condensate into the SHO ground state and generate ultra-narrow polariton lasing. image

In this report, we successfully fabricate a high performance β-phase Ga203 single-crystalline film deep ultraviolet (DUV) solar-blind photodetector. The hybrid Ga/GaO buffer layer method is proposed to promote the β-Ga203 film quality that hetero-grown on sapphire substrates using plasma-assisted molecular beam epitaxy (PA-MBE). Based on the 2-inch and smooth β-Ga203 single crystalline film, the solar-blind detector is constructed by interdigitated Au-electrode with metal-semiconductor-metal structure. The dark-state current of device is low as 40 pA, meanwhile the UV photon responsibility 234 mA/W at peak of 219 nm. Moreover, the devices exhibited an ultrafast transient characteristic for DUV signals with a fast-rising time of 3 μs and decay time of 23 μs. High contrast two-dimension scanning image has been recorded using such DUV photodetector as a sensor in an imaging system. The excellent performances of device could be attributed to the high crystalline quality of β-Ga2O3, and giant field mobility in Schottky junction. Our results present a significant step towards future applications of two-dimension array DUV photodetector based on larger scale β-Ga203 heteroepitaxy film.

With the progress of wide bandgap semiconductors, compact solid-state light-emitting devices for the ultraviolet wavelength region are of considerable technological interest as alternatives to conventional ultraviolet lamps in recent years. Here, the potential of aluminum nitride (AlN) as an ultraviolet luminescent material was studied. An ultraviolet light-emitting device, equipped with a carbon nanotube (CNT) array as the field-emission excitation source and AlN thin film as cathodoluminescent material, was fabricated. In operation, square high-voltage pulses with a 100 Hz repetition frequency and a 10% duty ratio were applied to the anode. The output spectra reveal a dominant ultraviolet emission at 330 nm with a short-wavelength shoulder at 285 nm, which increases with the anode driving voltage. This work has explored the potential of AlN thin film as a cathodoluminescent material and provides a platform for investigating other ultrawide bandgap (UWBG) semiconductors. Furthermore, while using AlN thin film and a carbon nanotube array as electrodes, this ultraviolet cathodoluminescent device can be more compact and versatile than conventional lamps. It is anticipated to be useful in a variety of applications such as photochemistry, biotechnology and optoelectronics devices.

We successfully fabricate a high performance β -phase (In 0.09 Ga 0.91 ) 2 O 3 single-crystalline film deep ultraviolet (DUV) solar-blind photodetector. The 2-inches high crystalline quality film is hetero-grown on the sapphire substrates using the plasma-assisted molecular beam epitaxy (PA-MBE). The smooth InGaO single crystalline film is used to construct the solar-blind DUV detector, which utilized an interdigitated Ti/Au electrode with a metal–semiconductor–metal structure. The device exhibits a low dark current of 40 pA (0 V), while its UV photon responsivity exceeds 450 A/W (50 V) at the peak wavelength of 232 nm with illumination intensity of 0.21 mW/cm 2 and the UV/VIS rejection ratio ( R 232 nm / R 380 nm ) exceeds 4 × 10 4 . Furthermore, the devices demonstrate ultrafast transient characteristics for DUV signals, with fast-rising and fast-falling times of 80 ns and 420 ns, respectively. This excellent temporal dynamic behavior can be attributed to indium doping can adjust the electronic structure of Ga 2 O 3 alloys to enhance the performance of InGaO solar-blind detectors. Additionally, a two-dimensional DUV scanning image is captured using the InGaO photodetector as a sensor in an imaging system. Our results pave the way for future applications of two-dimensional array DUV photodetectors based on the large-scale InGaO heteroepitaxially grown alloy wide bandgap semiconductor films.

In this report, we successfully fabricate a high performance beta-phase Ga203 single-crystalline film deep ultraviolet (DUV) solar-blind photodetector. The hybrid Ga/GaO buffer layer method is proposed to promote the quality of beta-Ga203 film that hetero-grown on sapphire substrates using plasma-assisted molecular beam epitaxy (PA-MBE). Based on the 2-inch and smooth beta-Ga203 single crystalline film, the solar-blind detector is constructed by interdigitated Au-electrode with metal-semiconductor-metal structure. The dark-state current of device is low as 40 pA, meanwhile the UV photon responsibility > 234 mA/W at peak of 219 nm. Moreover, the device exhibites an ultrafast transient characteristic for DUV signals with a fast-rising time of 3 mu s and decay time of 23 mu s. High contrast two-dimension scanning image has been recorded using such DUV photodetector as a sensor in an imaging system. The excellent performances of device could be attributed to the high crystalline quality of beta-Ga2O3, and giant field mobility in Schottky junction. Our results present a significant step towards future application of two-dimension array DUV photodetector based on larger scale beta-Ga203 heteroepitaxy film.

Exciton-polaritons are hybrid bosons that define thepeculiar interactionbetween the semiconductor and the optical cavity. The ultra-low effectivemass of polariton inherited from its photon fraction benefits theefficient Bose-Einstein condensation process. Due to the uniquesuperfluidity of polariton condensate, the persistent angular momentumof the system will facilitate plenty of chiral phenomena, such asthe spin precession, the spin-orbit coupling, and the emergenceof quantum vortices. Here, we report a chiral polariton laser viarobust spin-polarization of polariton condensation at room temperature.The self-formed chirality of the microcavity breaks the spatial inversionsymmetry and lifts the energy degeneracy of polariton spin doubletsby a considerable value of 11 meV, which can be demonstrated by theangle-resolved spectra recorded after a Wollaston prism. The bosoniccondensation only occurs in the low-energy spin-up polaritons, resultingin polariton lasing with stable right-circular (sigma(+)) polarization. The second-order coherence of a polariton chirallaser is determined by performing the Hanbury Brown-Twiss measurement,which indicates the quantum phase transition during the condensationprocess. Moreover, the robustness of the chirality of polariton lasingis demonstrated, and the basic physical mechanisms of the system areillustrated by the generalized Gross-Pitaevskii (G-P)equation. The results set solid building blocks for the developmentof chiral quantum photonics and spin polaritonics.

Nonlinear multiphoton absorption (MPA) upconversion lasers have critical applications in fluorescence imaging probes and biological photonics. Here, we report the realization of ultralow-threshold six-photon-excited upconversion lasing through cavity quantum electrodynamics effects in a plasmonic microcavity. The value of the Purcell factor (Fp) in hybrid whisper-gallery mode (WGM) is enhanced five-fold relative to a bare microwire (MW), which enhances the nonlinear light-matter interactions dramatically. Compared with a MW, the threshold of six-photon upconversion WGM lasing is reduced by one order magnitude due to plasmonic enhancement effects. In addition, the temperature and polarization characteristics of upconversion lasing via a plasmonic-WGM approach show a distinct evolution, different from a bare MW. This work paves the way for extreme nonlinear optics, taking advantage of the processability and high Purcell factor of plasmonic microcavities.

In the progress of nanoengineering of noble metals, the extreme nonlinear optics within nanometric volumes is of great research interest in recent years. In particular, plasmonic nanostructures offer unique route for enhancing high-order harmonic generation and other nonlinear optical progress. Here, we report that strong third harmonic emission in zinc oxide (ZnO) microbelts (MBs) via a strong localization of electromagnetic field caused by localized surface plasmon resonances. In MB/Au-nanoparticles composite, it was demonstrated that the intensity of third-harmonic generation (THG) was enhanced by a factor of five compared to bare MB. Additionally, the polarization characteristics of THG in the same system were illustrated in detail. With respect to the bare MB, the polarization degree of THG was improved significantly. The nonlinear polarization features can be attributed to the crystal structure and the ensemble of anisotropic plasmonic hot spots on the surface of Au nanoparticles. Finally, intrinsic enhancement process of THG was explored comprehensively by finite difference time domain method. The simulation results are consistent with our experimental observation.