Plasmonic field confinement for separate absorption-multiplication in InGaAs nanopillar avalanche photodiodes

Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III–V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure

Monolithic InGaAs nanowire array lasers on silicon-on-insulator operating at room temperature

Chip-scale integrated light sources are a crucial component in a broad range of photonics applications. III–V semiconductor nanowire emitters have gained attention as a fascinating approach due to their superior material properties, extremely compact size, and capability to grow directly on lattice-mismatched silicon substrates. Although there have been remarkable advances in nanowire-based emitters, their practical applications are still in the early stages due to the difficulties in integrating nanowire emitters with photonic integrated circuits. Here, we demonstrate for the first time optically pumped III–V nanowire array lasers monolithically integrated on silicon-on-insulator (SOI) platform. Selective-area growth of InGaAs/InGaP core/shell nanowires on an SOI substrate enables the nanowire array to form a photonic crystal nanobeam cavity with superior optical and structural properties, resulting in the laser to operate at room temperature. We also show that the nanowire array lasers are effectively coupled with SOI waveguides by employing nanoepitaxy on a prepatterned SOI platform. These results represent a new platform for ultracompact and energy-efficient optical links and unambiguously point the way toward practical and functional nanowire lasers

InGaAs-GaAs nanowire avalanche photodiodes toward single-photon detection in free-running mode

Single-photon detection at near-infrared (NIR) wavelengths is critical for light detection and ranging (LiDAR) systems used in imaging technologies such as autonomous vehicle trackers and atmospheric remote sensing. Portable, high-performance LiDAR relies on silicon-based single-photon avalanche diodes (SPADs) because of their extremely low dark count rate (DCR) and afterpulsing probability, but their operation wavelengths are typically limited up to 905 nm. Although InGaAs-InP SPADs offer an alternative platform to extend the operation wavelengths to eye-safe ranges, their high DCR and afterpulsing severely limit their commercial applications. Here we propose a new separate absorption and multiplication avalanche photodiode (SAM-APD) platform composed of vertical InGaAs–GaAs nanowire arrays for single-photon detection. Among a total of 4400 nanowires constituting one photodiode, each avalanche event is confined in a single nanowire, which means that the avalanche volume and the number of filled traps can be drastically reduced in our approach. This leads to an extremely small afterpulsing probability compared with conventional InGaAs-based SPADs and enables operation in free-running mode. We show a DCR below 10 Hz, due to reduced fill factor, with photon count rates of 7.8 MHz and timing jitter less than 113 ps, which suggest that nanowire-based NIR focal plane arrays for single-photon detection can be designed without active quenching circuitry that severely restricts pixel density and portability in NIR commercial SPADs. Therefore, the proposed work based on vertical nanowires provides a new degree of freedom in designing avalanche photodetectors and could be a stepping stone for high-performance InGaAs SPADs

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Nanopillar Optical Antenna Avalanche Detectors

Avalanche photodetectors (APDs) are essential components in active imaging systems requiring both ultrafast response times to measure photon time of flight and high gains to detect low photon fluxes. APDs improve system Signal to Noise Ratio by combining photon detection and amplification eliminating the need for front end amplifiers. An emerging trend in active imaging focal plane array technologies is reducing the pixel pitch (detector volume) for higher resolution images. However, there is an inherent trade-off between reduced detector volume and APD figures of merit. This dissertation will focus on the design, fabrication and electro-optic characterization of a novel detector architecture "3D Nanopillar Optical Antenna Avalanche Detectors" (3D-NOAADs) for shrinking both the absorption and multiplication volumes using III-V nanopillars, while enhancing the optical absorption via a self aligned 3D plasmonic antenna. Wavelength tuning and hybridization of the optical absorption via Surface Plasmon Polariton Bloch Waves (SPP-BWs) and Localized Surface Plasmon Resonances (LSPRs) will be discussed. Photo-generated carrier transport from the absorption region into the multiplication region and subsequent impact ionization will also be discussed. Single pixel 3D-NOAADs exhibit substantially lower excess noise factors compared to bulk, low breakdown voltages ~ 8 V and gain-bandwidth products > 100 GHz

Electrical Defect State Distribution in Single Crystal ZnO Schottky Barrier Diodes

The characterization of defect states in a hydrothermally grown single crystal of ZnO was performed using deep-level transient spectroscopy in the temperature range of 77–340 K. The native intrinsic defect energy level within the ZnO band gap occurred in the depletion region of ZnO Schottky barrier diodes. A major defect level was observed, with a thermal activation energy of 0.27 eV (E3) within the defect state distribution from 0.1 to 0.57 eV below the conduction band minimum. We confirmed the maximum defect concentration to be 3.66 × 1016 cm−3 at 0.27 eV (E3). As a result, we clearly confirmed the distribution of density of defect states in the ZnO band gap

Nanopillar array band-edge laser cavities on silicon-on-insulator for monolithic integrated light sources

A simple and unique laser scheme comprised of a finite-size nanopillar array on a silicon-on-insulator grating layer is introduced for realizing an on-chip monolithically integrated light source. A photonic band-edge mode, confined by the grating substrate in the vertical direction, shows a quality factor as high as 4000. We show that the proposed laser cavity allows direct coupling into a waveguide, which is essential for monolithic integration. In addition, III-V semiconductornanopillars are grown on a silicon-on-insulator grating substrate in order to demonstrate the feasibility of epitaxy on 3D surfaces. These results provide a practical solution for on-chip integration of a monolithic light source

Diode characteristics approaching bulk limits in GaAs nanowire array photodetectors

We present the electrical properties of p–n junction photodetectors comprised of vertically oriented p-GaAs nanowire arrays on the n-GaAs substrate. We measure an ideality factor as low as n = 1.0 and a rectification ratio >108 across all devices, with some >109, comparable to the best GaAs thin film photodetectors. An analysis of the Arrhenius plot of the saturation current yields an activation energy of 690 meV—approximately half the bandgap of GaAs—indicating generation–recombination current from midgap states is the primary contributor to the leakage current at low bias. Using fully three-dimensional electrical simulations, we explain the lack of a recombination current dominated regime at low forward bias, as well as some of the issues related to analysis of the capacitance–voltage characteristics of nanowire devices. This work demonstrates that, through proper design and fabrication, nanowire-based devices can perform as well as their bulk device counterparts