Thirty years ago, Coullet et al. proposed that a special optical field exists in laser cavities bearing some analogy with the superfluid vortex. Since then, optical vortices have been widely studied, inspired by the hydrodynamics sharing similar mathematics. Akin to a fluid vortex with a central flow singularity, an optical vortex beam has a phase singularity with a certain topological charge, giving rise to a hollow intensity distribution. Such a beam with helical phase fronts and orbital angular momentum reveals a subtle connection between macroscopic physical optics and microscopic quantum optics. These amazing properties provide a new understanding of a wide range of optical and physical phenomena, including twisting photons, spin-orbital interactions, Bose-Einstein condensates, etc., while the associated technologies for manipulating optical vortices have become increasingly tunable and flexible. Hitherto, owing to these salient properties and optical manipulation technologies, tunable vortex beams have engendered tremendous advanced applications such as optical tweezers, high-order quantum entanglement, and nonlinear optics. This article reviews the recent progress in tunable vortex technologies along with their advanced applications.

/pdf/optical-vortices-30-years-on-oam-manipulation-from-2yknluuuga.pdf

Optical vortices 30 years on: OAM manipulation from topological charge to multiple singularities

Abstract This article reviews recent progress leading to the generation of optical vortex beams. After introducing the basics of optical vortex beams and their promising applications, we summarized different approaches for optical vortex generation by discrete components and laser cavities. We place particular emphasis on the recent development of vortex generation by the planar phase plates, which are able to engineer a spiral phasefront via dynamic or geometric phase in nanoscale, and highlight the independent operation of these two different phases which leads to a multifunctional optical vortex beam generation and independent spin-orbit interaction. We also introduced the recent progress on vortex lasing, including vortex beam generation from the output of bulk lasers by modification of conventional laser cavities with phase elements and from integrated on-chip microlasers. Similar approaches are also applied to generate fractional vortex beams carrying fractional topological charge. The advanced technology and approaches on design and nanofabrications enable multiple vortex beams generation from a single device via multiplexing, multicasting, and vortex array, open up opportunities for applications on data processing, information encoding/decoding, communication and parallel data processing, and micromanipulations.

/pdf/recent-advances-on-optical-vortex-generation-1z9athjta7.pdf

Recent advances on optical vortex generation

Interface engineering and chemistry of Hf-based high-k dielectrics on III–V substrates

Recent years have witnessed GaN-based devices delivering their promise of unprecedented power and frequency levels and demonstrating their capability as an able replacement for Si-based devices. High-electron-mobility transistors (HEMTs), a key representative architecture of GaN-based devices, are well-suited for high-power and high frequency device applications, owing to highly desirable III-nitride physical properties. However, these devices are still hounded by issues not previously encountered in their more established Siand GaAs-based devices counterparts. Metal–insulator–semiconductor (MIS) structures are usually employed with varying degrees of success in sidestepping the major problematic issues such as excessive leakage current and current instability. While different insulator materials have been applied to GaN-based transistors, the properties of insulator/III-N interfaces are still not fully understood. This is mainly due to the difficulty of characterizing insulator/AlGaN interfaces in a MIS HEMT because of the two resulting interfaces: insulator/AlGaN and AlGaN/GaN, making the potential modulation rather complicated. Although there have been many reports of low interface-trap densities in HEMT MIS capacitors, several papers have incorrectly evaluated their capacitance–voltage (C–V) characteristics. A HEMT MIS structure typically shows a 2-step C–V behavior. However, several groups reported C–V curves without the characteristic step at the forward bias regime, which is likely to the high-density states at the insulator/ AlGaN interface impeding the potential control of the AlGaN surface by the gate bias. In this review paper, first we describe critical issues and problems including leakage current, current collapse and threshold voltage instability in AlGaN/GaN HEMTs. Then we present interface properties, focusing on interface states, of GaN MIS systems using oxides, nitrides and high-κ dielectrics. Next, the properties of a variety of AlGaN/GaN MIS structures as well as different characterization methods, including our own photo-assisted C–V technique, essential for understanding and developing successful surface passivation and interface control schemes, are given in the subsequent section. Finally we highlight the important progress in GaN MIS interfaces that have recently pushed the frontier of nitride-based device technology.

/pdf/insulated-gate-and-surface-passivation-structures-for-gan-16325xp5v2.pdf

Insulated gate and surface passivation structures for GaN-based power transistors

Solar photovoltaic energy optimization methods, challenges and issues: A comprehensive review

A GaN MIS-HEMT with nitrogen (N)-passivation for power device applications is demonstrated. In this letter, nitrogen radicals were adopted to recover nitrogen-vacancy-related defects which were formed due to the thermal decomposition and evaporation of nitrogen atoms from GaN surface during high-temperature process. Besides, nitrogen radicals can also remove impurities and reduce surface dangling bonds by forming Ga-N bonds on the SiN/GaN interface. With N-passivation, the device shows high ON/OFF current ratio, steep subthreshold slope, low OFF-state leakage current, high breakdown voltage, and improved dynamic ON-resistance. The device reliability under high-electric field stress was also improved as a result.

GaN MIS-HEMTs With Nitrogen Passivation for Power Device Applications

We develop a novel method of creating optical vortex array by the conversion of a standing-wave Laguerre-Gaussian (LG) mode. Theoretically, by employing the transformational relation, the standing-wave LG mode is verified to be transformed from a pair of crisscrossed Hermite-Gaussian (HG) modes, embedded with optical vortex array, consists of a TEMn,m mode and a TEMm,n mode. Due to close correspondence between the transformational relation and the mode conversion of astigmatic lenses, we successfully generate the optical vortex array by transforming a standing-wave LG mode into the crisscrossed HG modes via a π/2 cylindrical lens mode converter. The investigation may provide useful insight in the study of the vortex light beam and its further applications.

https://ir.nctu.edu.tw:443/bitstream/11536/8842/1/000290852800027.pdf

Generation of optical vortex array with transformation of standing-wave Laguerre-Gaussian mode.

The effects of plasma enhanced atomic layer deposition (PEALD)-AlN interfacial passivation layer (IPL) on the Al
 2
O
 3
/In
 0.53
Ga
 0.47
As interfaces qualities are studied with different plasma powers. The improvement in electrical properties, including capacitance-voltage (C-V) hysteresis, frequency dispersion, and interface state densities (Dit) are demonstrated on the Al
 2
O
 3
/n, p-In
 0.53
Ga
 0.47
As MOS capacitors. The excellent C-V behaviors are observed on both type of In
 0.53
Ga
 0.47
As-based MOS devices by performing a thin AlN-IPL at the plasma power of 150 W. To explore the interaction between PEALD-AlN layer and In
 0.53
Ga
 0.47
As surface, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analyses have also been characterized.

Electrical Characteristics of n, p-In 0.53 Ga 0.47 As MOSCAPs With In Situ PEALD-AlN Interfacial Passivation Layer

The impact of in situ plasma-enhanced atomic layer deposition passivation on the electrical properties of HfO2/In0.53Ga0.47As metal–oxide–semiconductor capacitors (MOSCAPs) has been studied. Excellent interface quality of high- $k$ /III–V is achieved by aluminum nitride (AlN) interfacial passivation layer, including strong inversion behaviors and unpinned Fermi level. The band alignment of HfO2/AlN/In0.53Ga0.47As structure with the valence band offsets of 2.81 ± 0.1 eV and the conduction band offsets of 1.9 ± 0.1 eV was obtained. Better interface and optimized high- $k$ dielectric qualities are achieved using post remote-plasma treatment with either N2/H2 or NH3 gases. Sub-nanometer equivalent oxide thickness HfO2/AlN/In0.53Ga0.47As MOSCAPs with low interface trap density and low leakage current density have been characterized.

Plasma Enhanced Atomic Layer Deposition Passivated HfO 2 /AlN/In 0.53 Ga 0.47 As MOSCAPs With Sub-Nanometer Equivalent Oxide Thickness and Low Interface Trap Density

Yueh Chin Lin

Papers

GaN MIS-HEMTs With Nitrogen Passivation for Power Device Applications

Generation of optical vortex array with transformation of standing-wave Laguerre-Gaussian mode.

Electrical Characteristics of n, p-In 0.53 Ga 0.47 As MOSCAPs With In Situ PEALD-AlN Interfacial Passivation Layer

Plasma Enhanced Atomic Layer Deposition Passivated HfO 2 /AlN/In 0.53 Ga 0.47 As MOSCAPs With Sub-Nanometer Equivalent Oxide Thickness and Low Interface Trap Density

RF loss mechanisms in GaN-based high-electron-mobility-transistor on silicon: Role of an inversion channel at the AlN/Si interface