Research interests in two-dimensional (2D) magnets have surged since the experimental discovery of atomic layers of Cr2Ge2Te6 and CrI3 in 2017. Through continuous efforts, additional intrinsic 2D magnets, such as Fe3GeTe2 and VSe2, have been experimentally realized, although their variety remains limited. Beyond the intrinsic 2D magnets, numerous artificially designed 2D magnetic materials have emerged, among which 2D Janus magnets become a significant category. Janus monolayer represents an exciting class of 2D materials characterized by distinct atomic species on their upper and lower surfaces. Recent studies reveal that 2D Janus materials, with their broken mirror symmetry, exhibit a range of novel properties, including large Rashba spin-orbit coupling, antiferromagnets AFM-FM transition, enhanced magnetoelectric coupling, etc. In this review, we summarize the recent progress in 2D Janus magnets, including both the theoretical results and experimental synthesis.
III-nitride based micro light-emitting diodes (microLEDs or μLEDs) have rapidly emerged as a leading platform for next-generation photonic technologies, spanning micro-displays, visible light communications and data-centric computing. By scaling spontaneous-emission devices to micrometre dimensions, microLEDs enable high brightness, fast modulation and dense integration, translating fundamental principles of optical confinement, carrier recombination and light–matter interaction into practical, electrically injected emitters. This review provides a comprehensive overview of the current status of developing III-nitride microLED technologies, while examining the fundamental physics that governs their operation and scaling behaviour. This article also summarises recent advances in materials, device architectures and fabrication, and assess emerging applications in ultra-high-resolution micro-displays, high-speed visible light communication and optical interconnects for artificial intelligence systems. Critical challenges for further developing microLED technologies and strategies based on materials engineering, device innovation and system co-design are discussed to enable scalable, high-performance microLED technologies.
III-nitride materials, including aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), and their alloys, exhibit exceptional electrical, optical, and acoustic properties, making them highly versatile and promising for hybrid information processing in both classical and quantum regime. This review provides an overview of their crystal structures, growth methods, electrical and optical characteristics, nonlinear optical phenomena, and piezoelectric interactions. We highlight recent advancements in integrated photonic devices based on these materials and discuss future prospects for hybrid quantum and nonlinear photonic systems.
GaN-based laser diodes (LDs) have emerged as a transformative technology for next-generation optoelectronics, extending their reach beyond display and lighting into high-speed optical communications, optical interconnects, and optical computing. This review provides a comprehensive analysis of the state-of-the-art in GaN-based laser technology, bridging fundamental material science with system-level applications. We begin by critically examining breakthroughs in III-nitride material growth, including the synthesis of low-defect-density bulk substrates and advanced epitaxial techniques designed to mitigate strain-induced polarization fields and enhance carrier injection efficiency in quantum well heterostructures. Building on this material foundation, we detail the progress in device engineering across the ultraviolet, violet, blue, and green spectral regions. Notably, recent optimizations in active region design and device structures have enabled blue LDs to achieve modulation bandwidths exceeding 8 GHz and data transmission rates beyond 36 Gbps, while green lasers are showing increasing viability for underwater and plastic optical fiber communications. Furthermore, the review explores the emerging role of utilizing GaN LDs in optical computing and optoelectronic logic devices, where their high modulation speed and energy efficiency offer distinct advantages over traditional electronic counterparts. Finally, we discuss remaining bottlenecks in thermal dissipation, reliability, and photonic integration, outlining a roadmap for future research to unlock the full potential of GaN-based integrated photonics.
Deep learning (DL) has become an important tool in digital holography (DH), enabling data-driven learning of complex inverse mappings directly from holographic measurements. Early DL-assisted DH demonstrated the feasibility of this approach but often relied on large labeled datasets and lacked explicit physical interpretability. In recent years, advances in DL methodologies have begun to address these limitations. This review examines three major developments that are reshaping the field: innovative training strategies for data-efficient learning, the integration of physical priors for improved interpretability and physical consistency, and advanced network architectures capable of extracting richer representations from holographic data. By organizing recent progress from this methodological perspective, we provide an updated overview of how modern DL techniques are expanding the capabilities of DH. We conclude with a forward-looking perspective, identifying promising but underexplored DL directions expected to drive significant future advancements in DH applications.
Single quantum emitters (SQEs) in two-dimensional (2D) materials offer a promising platform for quantum-light generation with compatibility for electrostatic control, van der Waals heterostructures, and nanophotonic integration. This review summarizes recent progress in integrating SQEs in transition metal dichalcogenides (TMDs) and hexagonal boron nitride (hBN) with electrical and photonic device structures. We discuss electrically driven emission, electrostatic tuning and charge stabilization, and the device and circuit considerations relevant to high-rate pulsed operation. We further review waveguide, on-chip resonator, and off-chip cavity platforms designed to improve emission collection, directionality, and radiative performance. Across these developments, we highlight how material properties, device geometry, and the local electromagnetic and electrostatic environment influence key source characteristics, including single-photon purity, brightness, spectral stability, linewidth, coherence, and photon indistinguishability. Particular attention is given to the distinct opportunities and constraints of localized defect-bound excitons in TMDs and defect-based color centers in hBN. We identify remaining challenges in reproducible electrical operation, low-noise device environments, spectral matching, and scalable optical interfacing. Together, these advances establish a foundation for integrated 2D-material quantum-light sources with controllable emission and efficient optical functionality.
Plasmonic nanolasers overcome the diffraction limit by coupling photons with surface plasmons, enabling ultra-small mode volumes and near-unity β-factors, leading to thresholdless lasing. These unique features support ultrafast modulation and strong light–matter interaction, making them attractive for next-generation photonics. This review surveys recent advances in cavity architectures, active modulation strategies, and emerging materials. We highlight applications in optoelectronic integration, quantum photonics, and biosensing, while outlining persistent challenges including loss, fabrication, and scalable electrical injection, as well as thermal management for continuous-wave operation and device reliability. Looking ahead, innovations in materials, hybrid cavity design, and Si-compatible integration are expected to transform plasmonic nanolasers from laboratory demonstrations into foundational building blocks for future computing, communication, and sensing.
Quantum optics, the study of nonclassical states of light, has long been pursued and recently evolved into integrated quantum photonics. That is, transforming the field into a viable technology for scalable, stable, and reconfigurable quantum information processing, secure communication, and sensing systems beyond the limits of classical optics. Among the various integrated material platforms, thin-film lithium niobate (TFLN) has recently attracted significant attention for quantum applications, due to its strong second-order nonlinear and electro-optic (EO) properties, and wide transparency range. Unlike conventional bulk lithium niobate photonics, which suffers from low optical confinement and limited wafer-scale scalability, TFLN enables submicron waveguides, tight bending radii, and dense photonic integration, leading to enhanced nonlinear interactions and compact device and circuit footprints. In addition, TFLN has potential for heterogeneous integration with other materials for access to other functionalities on the same chip, e.g., photodetection, low-loss passive optics, and third-order nonlinear optics.This paper reviews the progress of integrated quantum photonics based on TFLN, highlighting early groundbreaking works, recent experimental milestones, and future opportunities and challenges. We start with an overview of the progress in classical EO devices, which are indispensable building blocks for quantum photonic integrated circuits such as cryogenic transducers. Background and progress in both second- and third-order nonlinear effects, such as frequency conversion, parametric effects, and related applications, like optical frequency combs, are reviewed. We will then focus on demonstrated quantum-optical effects on TFLN devices and circuits. Specifically, generation of high-brightness and spectrally pure quantum-correlated and entangled photons through spontaneous parametric down-conversion, as well as demonstrations of squeezed-light sources, are discussed. Moreover, we present an overview of experimental demonstrations of quantum key distribution and Hong–Ou–Mandel interferometry based on TFLN. Related works on quantum cryptography, i.e., photonic qubit encoding in the time, frequency, and polarization domains, are covered next. The final sections of this paper discuss heterogeneous integration with laser sources and superconducting photodetectors, and an outlook on the progress and challenges of reducing the optical propagation loss towards practical, fully-packaged, and low-loss quantum photonic systems on TFLN.
III-nitride nanowires (NWs) have emerged as a versatile platform for nanoscale optoelectronics, combining unique attributes such as strain relaxation, defect tolerance, strong carrier confinement, and compatibility with silicon backplanes. Advances in epitaxial growth techniques, including molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), and selective-area epitaxy (SAE), have enabled deterministic control over high-quality, compositionally flexible NW arrays. These breakthroughs have led to diverse device architectures, spanning Fabry-Pérot (FP) cavities, whispering gallery modes (WGM), plasmonic resonators, random cavities, and photonic crystal arrays, achieving low-threshold lasing, narrow linewidths, and spectral tunability. NW light-emitting diodes (LEDs) have further demonstrated polarization-free emission, geometry-driven color tuning, and monolithic full-color operation without phosphors, addressing long-standing challenges such as the “green gap” and scalable RGB integration. These structural and device-level advantages are now converging with the stringent requirements of next-generation AR/VR/XR micro-displays, which demand extreme luminance, sub-micron pixel pitches, narrow spectral linewidths, and directional emission for efficient coupling into waveguide optics. While conventional micro-LEDs face severe efficiency bottlenecks at deep submicron scales, NW lasers, particularly photonic-crystal and tunnel-junction surface-emitting designs, offer coherence, spectral purity, and engineered far-fields that are well aligned with immersive display engines. We further link these advances to system-level performance benchmarks, including luminance after optical combiners, spectral stability, power efficiency, and manufacturability. Finally, beyond displays, progress in tunnel junction integration and photonic-crystal NW surface-emitting lasers highlights the future application potential of this technology in on-chip photonic interconnects, quantum light sources, and emerging optical computing paradigms. By bridging nanoscale materials science with application-driven requirements, III-nitride NW lasers are positioned as a transformative platform for both optoelectronics and next-generation display technologies.
Classical light such as lasers and thermal radiation has long been utilized for spectroscopy to explore material structures and dynamics. However, quantum states of light open new avenues for ultrafast optics and spectroscopy, by the variation of their unique properties, e.g., entanglement and photon statistics, after interacting with materials. Quantum light possesses unique characteristics that distinguish it from classical light, particularly the phase-space distribution which reflects its fundamental quantum statistics and the quantum control protocol that may take advantage of noise reduction. This Review will focus on spectroscopic applications using entangled photons and squeezed light, in conjunction with quantum coherent control. We provide a brief introduction to the generation of the entangled and squeezed light, discussing their fundamental properties and connections to the control protocol that may enhance spectroscopic techniques. A microscopic theory for the spectroscopy and corresponding signals induced by certain transition processes is developed. Nonlinear optical signals induced by entangled photons for the coherent anti-Stokes Raman spectra (CARS) and the stimulated Raman spectra (SRS) are investigated. We further extend our efforts to the transient absorption process that enables real-time monitoring of the exciton transfer in the transition metal dichalcogenides (TMDs), namely, using the WS2 monolayer. This series of works on nonlinear optical spectroscopy using quantum light explicitly demonstrates the quantum supremacy in ultrafast spectroscopy through jointly enhancing the time and energy scales beyond the classical bound.
Micro-LEDs have emerged as promising light sources for high-resolution displays, yet their commercialization faces persistent challenges in simultaneously achieving high efficiency, extended operational lifespan, and spectral stability. Recent advances in understanding carrier dynamics within micro-LEDs, including injection, transport, spatial distribution, radiative recombination, and nonradiative recombination, have fundamentally driven the development of advanced epitaxial growth, mesa-etching techniques, and sidewall treatment. In addition to the traditional InGaN-based blue/green and AlGaInP-based red micro-LEDs, InGaN-based red micro-LEDs have demonstrated notable advancement in luminous characteristics. This review presents the cutting-edge epitaxial strategies and innovative sidewall treatment methodologies, while providing an assessment of their impacts on the performance of micro-LEDs.
As a branch of quantum materials, topological materials are noted for their topologically nontrivial band structures, massless Dirac or Weyl fermions, strong spin-orbit coupling, and boundary-protected states, endowed with exotic physical properties totally different from those of conventional insulators and metals. In this era of information intelligence, topological materials with unconventional properties have drawn increasing attention, with the growing demand for high-performance electronics, spintronics, optoelectronics, thermoelectrics, etc. Besides, compared to bulk forms, nanostructured topological materials are more compatible with electronic and optoelectronic applications in terms of device integration and fabrication. They also possess enhanced contributions from surface/edge states and geometry-regulated band structures. Therefore, there is a demand for manufacturing and studying nanostructured topological materials. With this motivation, recently there have been burgeoning explorations of nanostructured topological materials. In this review, we systematically summarize the exciting proceedings in both synthesis and characterizations of nanostructured topological materials. We start from the introduction of state-of-the-art synthesis methods, as well as their capability of structural control, feasibility, and potential for scaling up. Then, we summarize the characterization tools and the corresponding properties of nanostructured topological materials, in which the origins of these topologically-related physical properties and their nanostructure dependences are elaborated. Perspectives on the challenges and opportunities are also given in the final part to summarize the advances and propose possible directions in the field of nanostructured topological materials.
This review explores magnetic field-driven emergent phenomena across various material systems, emphasizing the pivotal roles of magneto-optical and nanoscopy techniques. We examine fundamental aspects of Landau electrodynamics in both 2D and 3D systems, including quantum Hall and topological magnetoelectric effects in graphene and topological insulators. Particularly attention is given to magnetic excitations and magnetopolaritons, such as surface magnon polaritons, magnetoplasmons, and magnetoexcitons in novel quantum materials, including quantum magnets and hybrid heterostructures. Advanced imaging techniques, such as scattering-type scanning near-field optical microscopy (SNOM) and microwave impedance microscopy, are showcased for their capability to resolve these phenomena with microscopic and nanoscopic resolution. These insights are complemented by discussions of advanced experimental approaches, including cryogenic environments, ultrafast pump-probe techniques, and the integration of magnetic fields into near-field optical methodologies. We further investigate the potential of these imaging techniques for unraveling complex magnetic orders, quantum phases, and correlated electronic behaviors. Finally, we offer perspectives on future research directions and highlight emerging opportunities in the evolving field of optical magneto-nanoscopy.
The semiconductor industry is increasingly reliant on advances in epitaxial technologies to meet the demands of high-performance applications such as advanced photonics, quantum computing, and power electronics. However, the nonlinear dynamics of crystal epitaxial growth, combined with stochastic interfacial fluctuations, present significant challenges. These challenges create fundamental difficulties between the control of empirical parameters and the stringent material quality requirements, which hinder systematic improvements in material performance. This paper reviews recent progress in Intelligent Epitaxy, a transformative framework that employs an autonomous architecture consisting of sensing, decision-making, and execution. This framework integrates machine learning with precise characterization and control through three core modules: the Multimodal Sensing Module, the Knowledge-Informed Decision Module, and the Adaptive Control Module. Together, these modules enable comprehensive monitoring of growth dynamics, causal analysis of the relationships between parameters, growth states, and outcomes, as well as the autonomous regulation of growth processes. Additionally, we discuss and address current challenges and issues in this field, providing insights and perspectives for future research. Our review aims to guide the development of a new technological trajectory that goes beyond traditional approaches, positioning intelligent epitaxy as the foundation for next-generation autonomous semiconductor manufacturing.
Micro-scale light-emitting diodes (micro-LEDs), with their high brightness, high resolution, and low power consumption, are emerging as a promising candidate for the next-generation display. Among them, InGaN red micro-LEDs, as a crucial component of full-color micro-displays, have attracted significant attention for their smaller size effect, higher thermal stability, and compatibility with blue and green micro-LED fabrication processes and so on, when compared to AlGaInP red micro-LEDs. However, for next-generation display technologies such as augmented reality (AR), InGaN red micro-LEDs still fall short of meeting the requirements. Specifically, the efficiency of InGaN red micro-LEDs with the ultra-small size needed for AR applications is still very low, necessitating a high working current density. Unfortunately, a high current density leads to a significant blueshift in the emission wavelength, which results in color deviation, failing to meet the requirements for red display devices. This review has introduced two approaches to address the aforementioned issues, namely enhancing the efficiency of InGaN red micro-LEDs or suppressing the blueshift, and has listed the performances of recent typical InGaN red micro-LEDs. Finally, the potential of InGaN red micro-LEDs in the full-color monolithic displays has been discussed.
Concentrating photovoltaics (CPV) use inexpensive optics to concentrate sunlight onto high efficiency solar cells. Over the past decade, the field of CPV has evolved from large systems aimed at grid-scale power generation toward microconcentrating photovoltaics (µCPV) that employ miniaturized cells and compact optics to address new, performance-driven applications such as agrivoltaics and space power. This review summarizes the development, present status, and future prospects of this emerging subfield. We discuss the main components that make up a typical µCPV system and highlight some of the key results achieved to date before concluding with a look forward at the milestones that will be needed to transition µCPV out of the lab and into the real world.
AlGaN/GaN-based high electron mobility transistors (HEMTs) hold significant technological importance due to their applications in power electronics, radio frequency (RF) amplifiers, and microwave communication systems. A critical factor affecting the performance of AlGaN/GaN HEMTs is the formation of high-quality ohmic contacts to the source and drain, which facilitates efficient carrier injection from metal electrodes to the semiconductor. Therefore, various approaches have been employed to achieve the formation of high-quality ohmic contacts. This review presents recent advancements in ohmic contact technology for AlGaN/GaN HEMTs. Specifically, we introduce and discuss contact technologies focusing on multilayer schemes under different annealing conditions, Au-free metallization schemes, surface treatments, non-traditional annealing processes, recess etching, selective area regrowth, and ion implantation.
