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The photosensitivity of silicon is inherently very low in the visible electromagnetic spectrum, and it drops rapidly beyond 800 nm in near-infrared wavelengths. Herein, we have experimentally demonstrated a technique utilizing photon-trapping surface structures to show a prodigious improvement of photoabsorption in one-micrometer-thin silicon, surpassing the inherent absorption efficiency of gallium arsenide for a broad spectrum. The photon-trapping structures allow the bending of normally incident light by almost ninety degrees to transform into laterally propagating modes along the silicon plane. Consequently, the propagation length of light increases, contributing to more than an order of magnitude improvement in absorption efficiency in photodetectors. This high absorption phenomenon is explained by FDTD analysis, where we show an enhanced photon density of states while substantially reducing the optical group velocity of light compared to silicon without photon-trapping structures, leading to significantly enhanced light-matter interactions. Our simulations also predict an enhanced absorption efficiency of photodetectors designed using 30 and 100-nanometer silicon thin films that are compatible with CMOS electronics. Despite a very thin absorption layer, such photon-trapping structures can enable high-efficiency and high-speed photodetectors needed in ultra-fast computer networks, data communication, and imaging systems with the potential to revolutionize on-chip logic and optoelectronic integration., Comment: 24 pages, 4 figures

Silicon photodiode-based CMOS sensors with backside-illumination for 300–1100 nm wavelength range were studied. We showed that a single hole in the photodiode increases the optical efficiency of the pixel. In near-infrared wavelengths, the enhancement allows 70% absorption in a $3~\mu \text{m}$ thick Si. It is $4\times $ better than that for the flat pixel. We compared different shapes and sizes of single hole and hole arrays. We have shown that a certain size and shape in single hole-based pixels contribute to stronger enhancement of optical efficiencies. The crosstalk was successfully reduced by employing trenches between pixels. We optimized the dimensions of the trenches to achieve minimal pixel separation for $1.12~\mu \text{m}$ pixels.

Avalanche and Single-Photon Avalanche photodetectors (APDs and SPADs) rely on the probability of photogenerated carriers to trigger a multiplication process. Photon penetration depth plays a vital role in this process. In silicon APDs, a significant fraction of the short visible wavelengths is absorbed close to the device surface that is typically highly doped to serve as a contact. Most of the photogenerated carriers in this region can be lost by recombination, get slowly transported by diffusion, or multiplied with high excess noise. On the other hand, the extended penetration depth of near-infrared wavelengths requires thick semiconductors for efficient absorption. This diminishes the speed of the devices due to the long transit time in the thick absorption layer that is required for detecting most of these photons. Here, we demonstrate that it is possible to drive photons to a critical depth in a semiconductor film to maximize their gain-bandwidth performance and increase the absorption efficiency. This approach to engineering the penetration depth for different wavelengths in silicon is enabled by integrating photon-trapping nanoholes on the device surface. The penetration depth of short wavelengths such as 450 nm is increased from 0.25 µm to more than 0.62 µm. On the other hand, for a long-wavelength like 850 nm, the penetration depth is reduced from 18.3 µm to only 2.3 µm, decreasing the device transit time considerably. Such capabilities allow increasing the gain in APDs by almost 400× at 450 nm and by almost 9× at 850 nm. This engineering of the penetration depth in APDs would enable device designs requiring higher gain-bandwidth in emerging technologies such as Fluorescence Lifetime Microscopy (FLIM), Time-of-Flight Positron Emission Tomography (TOF-PET), quantum communications systems, and 3D imaging systems.

Monolithic integration of high-speed, high-efficiency photodiodes with receiver electronics on a single silicon chip is a key to reduce cost and improve the performance of data centers’ short reach optical interconnects. We report a CMOS-compatible surface illuminated silicon PIN photodiode with integrated micro- and nano-scale holes that trap photons for longer interaction with semiconductors resulting in higher absorption efficiencies. The fabricated photodiode demonstrates more than 55% external quantum efficiency (EQE) at 850 nm, and a measured Full-Width at Half Maximum (FWHM) impulse response of 29 ps, 31 ps, and 34 ps at 15 V, 10 V, and 3 V reverse biases, respectively. Simulation results indicate the possibility of operation up to 12.5 Gb/s (NRZ) with no equalization.

The gain in Avalanche Photodiodes (APDs) and Single Photon Avalanche Diodes (SPADs) is dependent on the probability of photo-generated carriers to trigger an avalanche process, which is correlated to the depth where a photon is absorbed by the photodiode. For silicon photodiodes, most of the photons with wavelengths in the visible spectrum are absorbed near the surface in the highly doped contact regions where the recombination rate is high. Thus, they do not contribute significantly to the avalanche multiplication process. By integrating photon-trapping nanostructures, we facilitate deeper penetration of photons into the devices, enhancing light absorption to generate more carriers that can trigger the avalanche process. This improves the gain-bandwidth of silicon APDs and SPADs significantly. Photon-trapping nanoholes can reduce the thickness of silicon without compromising its quantum efficiency, while a perforated surface reduces the device capacitance improving the bandwidth. Therefore, the manipulation of light penetration depth using photon-trapping nanoholes leads to ultrafast high-gain photodetectors capable of detecting faint light signals particularly useful for low light applications such as fluorescent lifetime imaging microscopy and time-of-flight positron emission tomography.

Silicon photodetectors (PDs) operating at near‐IR wavelengths with high speed and high sensitivity are becoming critical for emerging applications, such as light detection and ranging (LIDAR) systems, quantum communications, and medical imaging. However, such PDs present a bandwidth‐absorption trade‐off at those wavelengths that have limited their implementation. Photon‐trapping (PT) structures address this trade‐off by enhancing the light–matter interactions, but maximizing their performance remains a challenge due to a multitude of factors influencing their design and fabrication. Herein, strategies to improve the PT effect while enhancing the speed of operation are investigated. By optimizing the design of PT structures and experimentally integrating them in high‐speed PDs, a simultaneous broadband absorption efficiency enhancement up to 1000% and a capacitance reduction of more than 50% are achieved. Empirical equations correlate the quantum efficiency of PDs with the physical properties of the PT structures, material characteristics, and limitations of the fabrication technologies. The results that are obtained open routes toward designing cost‐effective complementary metal–oxide‐semiconductor (CMOS)‐integrated receivers.

Due to relatively low responsivity at near infrared (NIR) wavelengths, surface-illuminated silicon (Si) photodiodes (PDs) are not attractive for ultra-fast data communication applications despite their CMOS-compatibility. Metal-semiconductor-metal (MSM) photodiodes are well-known for simplicity in fabrication compared to pin and pn junctions-based counterparts, but they usually work with lower efficiencies due to thin absorption layer that ensures high speed response. In this letter, we demonstrate a high efficiency and high-speed Si MSM PD with innovative photon-trapping surface structures. These wavelength-scale structures decrease the surface reflection and introduce laterally propagating waves parallel to the semiconductor surface. The responsivity of Si MSM PDs with the photon-trapping holes was measured to be ~0.59A/W, while the control devices without holes show ~0.08A/W. Such PDs with $50\mu \text{m}$ diameter and with 1 $\mu \text{m}$ finger spacing provide a pulse response of 60ps and 38ps full-width at half-maximum (FWHM) at 3V and 10V applied bias, respectively. Surface-illuminated PDs with these dimensions can offer easy optical coupling options for fiber optic links while offering complete CMOS compatibility.

In this paper, we present a rigorous coupled-wave analysis (RCWA) of absorption enhancement in all-silicon (Si) photodiodes with integrated hole arrays of different shapes and dimensions. The RCWA method is used to analyze the light propagation and trapping in the photodiodes on both Si-on-insulator (SOI) and bulk Si substrates for the datacom wavelength at about 850 nm. Our calculation and measurement results show that funnel-shaped holes with tapered sidewalls lead to low back-reflection. A beam of light undergoes a deflection subsequent to the diffraction in the hole array and generates laterally propagating waves. SOI substrates with oxide layers play an important role in reducing the transmission loss, especially for deflected light with higher-order diffraction from the hole array. Owing to laterally propagating modes and back-reflection on the SiO2 film, light is more confined in the thin Si layer on the SOI substrates compared to that on the bulk Si substrates. Experimental results based on fabricated devices support the predictions of the RCWA. Devices are designed with a 2-μm-thick intrinsic layer, which ensures ultrafast impulse response (full-width at half-maximum) of 30 ps. Measurements for integrated photodiodes with funnel-shaped holes indicate an enhanced external quantum efficiency of more than 55% on the SOI substrates. This represents more than 500% improvement compared to photodiodes without integrated phototrapping nanoholes.

Improving the time resolution and sensitivity of Silicon-based Single Photon Avalanche Photodetectors (Si-SPAD) across the entire visible spectrum is critical to improve image quality in biomedical imaging applications such as positron emission tomography or fluorescence lifetime imaging. This work reports on the feasibility of manipulating the penetration depth of photons with 450 nm wavelengths to enhance absorption in Si-SPAD by means of photon trapping structures. Optical-electrical simulations suggest light can be directed towards critical regions of the semiconductor increasing the absorption from 54 to 90% with only 1.2μm of silicon and enhancing the probability of avalanche by electrons that leads to higher multiplication gain and speed of operation.

Theory is proposed for nanohole silicon

This paper introduces an automated image processing method to analyze an architectural floor plan database. The floor plan information, such as the measurement of the rooms, dimension lines, and even the location of each room, can be automatically produced. This assists the real-estate agents to maximise the chances of the closure of deals by providing explicit insights to the prospective purchasers. With a clear idea about the layout of the place, customers can quickly make an analytical decision. Besides, it reduces the specialized training cost and increases the efficiency in business actions by understanding the property types with the greatest demand. Succinctly, this paper utilizes both the traditional image processing and convolutional neural networks (CNNs) to detect the bedrooms by undergoing the segmentation and classification processes. A thorough experiment, analysis, and evaluation had been performed to verify the effectiveness of the proposed framework. As a result, a three-class bedroom classification accuracy of ∼ 90% was achieved when validating on more than 500 image samples that consist of the different room numbers. In addition, qualitative findings were presented to manifest visually the feasibility of the algorithm developed.

Architecture is about evolution, there exist many types of architectural styles that depend on the geography, traditions, and culture of the particular regions. An architectural designer may have a similar preference in creating the new architectural building, which can be easily recognized from the physical attributes and characteristics. This paper performs an architect classification based on the outward appearance of the building. An architecture database with 100 images (ARC-100) that have balanced class distribution is constructed. Among the architectural buildings, the best performance is 71% for 5-class classification. Convolutional neural networks (CNNs) have demonstrated breakthrough performance on various classification tasks in recent studies, and even outperform human experts in specific tasks. Thus, for the baseline evaluation, multiple pretrained CNN models are employed with slight modifications. Prior to the feature extraction and classification processes, the removal of background noise is performed using two approaches: manually and automatically. The former approach requires high human intervention, while the latter utilizes the cutting-edge object segmentation technology, namely mask regional convolutional neural network (R-CNN). The illustration of the experiment training progress and the confusion matrix are reported, to allow further interpretation and analysis for the model trained. Notably, this is the first work that performs automatic classification based on architectural styles. This framework can be used to improve the cultural understanding and practices in providing education for holistic development and enhance the learning experience and progressions from an aesthetic perspective.

The article by Huang K-L et al. Effects of low-dose computed tomography (LDCT) screening on lung cancer contains a conclusion that is not consistent with the data presented. With reference to the National Lung Screening Trial (NLST) there are several flaws in the methodology overlooked. Also there is no significant reduction in deaths from all causes following the screening. Therefore any claim that the LDCT screening is superior to usual care is invalid.

We propose a novel spectral imaging technique with silicon photodiodes arrays having unique responsivity across a wide spectrum. Our method can detect random spectra with less than 2% standard deviation.

The ability to monolithically integrate high-speed photodetectors (PDs) with silicon (Si) can contribute to drastic reduction in cost. Such PDs are envisioned to be integral parts of high-speed optical interconnects in the future intrachip, chip-to-chip, board-to-board, rack-to-rack, and intra-/interdata center links. Si-based PDs are of special interest since they present the potential for monolithic integration with CMOS and BiCMOS very-large-scale integration and ultralarge-scale integration electronics. In the second part of this review, we present the efforts pursued by the researchers in engineering and integrating Si, SiGe alloys, and Ge PDs to CMOS and BiCMOS electronics and compare the performance of recently demonstrated CMOS-compatible ultrafast surface-illuminated Si PD with absorption-enhancing low-dimensional structures. We discuss the advantages and challenges of device design with micro-/nanostructures, and finally, we conclude with the future directions that low-dimensional structures can offer to potentially cause a paradigm shift in high-performance PD design for various applications such as extended-reach links, single-photon detection, light detection and ranging, and high-performance computing.

Research efforts have been devoted to glue-laminated bamboo (GLB) as an alternative to engineered timber. However, some research has shown that GLB exhibits brittle failure at smaller displacement when compared with Glulam. To address this issue and enhance the GLB mechanical performance, we propose to use Glass Fibre Reinforced Polymer (GFRP) to reinforce the GLB in the moment-resisting connections. A total of 24 GLB connections were tested to discuss the effectiveness of different reinforcement strategies. The test results showed that the connections reinforced by GFRP on both sides underwent significantly higher deformation before reaching the ultimate strength, which demonstrates the enhanced deformability of the connections. The ultimate moment-resisting strength could increase up to 37% compared to the unreinforced ones. Push-over analyses were carried out in this study to understand the effectiveness of different reinforcement strategies on the connections in portal frames, and this justifies the use of double-sided GFRP reinforcement.

Theory is proposed for nanohole silicon pin/nip photodetector (PD) physics, promising devices in the future data communications and lidar applications. Photons and carriers have wavelengths of 1 m and 5 nm, respectively. We propose vertical nanoholes having 2D periodicity with a feature size of 1 m will produce photons slower than those in bulk silicon, but carriers are unchanged. Close comparison to experiments validates this view. First, we study steady state nanohole PD current as a function of illumination power, and results are attributed to the voltage drop partitions in the PD and electrodes. Nanohole PD voltage drop depends on illumination, but series resistance voltage drop does not, and this explains experiments well. Next, we study transient characteristics for the sudden termination of light illumination. Nanohole PDs are much faster than flat PDs, and this is because the former produces much less slow diffusion minority carriers. In fact, most photons have already been absorbed in the i-layer in nanohole PDs, resulting in much less diffusion minority carriers at the bottom highly doped layer. Why diffusion in PDs is slow and that in bipolar junction transistors is quick is discussed in Appendix.

A surface-illuminated silicon photodiode with both high speed and usable external quantum efficiency from 900 to 1000 nm wavelength is highly desirable for intra/inter data center Ethernet communications, high performance computing, and laser radar application. Such Si photodiodes have the potential for monolithic integration to CMOS integrated circuits which can significantly reduce the cost of data transmission per gigabit below one US dollar. To overcome silicon’s intrinsic weakness of absorption in these wavelengths, photon-trapping microstructured hole arrays are etched into the silicon surface, and the operational wavelengths of a high-speed silicon PIN photodiode are extended to 1000 nm. In this paper, the design and fabrication of such photon-trapping structures integrated into all-silicon photodiodes with significantly reduced absorption layer thicknesses to achieve high external quantum efficiency and fast response are presented. Different designs and geometries of the submicron holes on the sil...

High-speed, high-efficiency photodetectors play an important role in optical communication links that are increasingly being used in data centres to handle higher volumes of data traffic and higher bandwidths, as big data and cloud computing continue to grow exponentially. Monolithic integration of optical components with signal-processing electronics on a single silicon chip is of paramount importance in the drive to reduce cost and improve performance. We report the first demonstration of micro- and nanoscale holes enabling light trapping in a silicon photodiode, which exhibits an ultrafast impulse response (full-width at half-maximum) of 30 ps and a high efficiency of more than 50%, for use in data-centre optical communications. The photodiode uses micro- and nanostructured holes to enhance, by an order of magnitude, the absorption efficiency of a thin intrinsic layer of less than 2 µm thickness and is designed for a data rate of 20 gigabits per second or higher at a wavelength of 850 nm. Further optimization can improve the efficiency to more than 70%. Light-trapping nanoscale holes are exploited to improve the speed and efficiency of silicon photodiodes with intrinsic layers less than 2 μm thick.

The photon trapping nano-structures help to enhance quantum efficiency in ultra-thin photodetectors that allows to design faster devices. The study shows simulations for light trapping and carriers transport in Si MSM photodetector with micro-hole structure at wavelength 800–950nm.

Light trapping nanostructures implemented in PIN silicon photodetectors demonstrates more than 500% improvement of quantum efficiency at 905nm wavelength, enabling their implementation for short range, high resolution and low-cost LIDAR systems, required in new data driven applications such as robotics, agriculture and manufacturing.