M. Saif Islam

• Ph.D.
• University of California, Davis

The applications of hyperspectral imaging across disciplines such as healthcare, automobiles, forensics, and astronomy are constrained by the requirement for intricate filters and dispersion lenses. By utilization of devices with engineered spectral responses and advanced signal processing techniques, the spectral imaging process can be made more a...

The study proposes an ultra-thin back side illuminated (BSI) and top-illuminated, Ge on Si photodetector (PD), for 1 to 1.4 microns wavelength range. The Ge thickness of 350 nm allows us to achieve high-speed performance at >60 GHz, while the nanostructure at the bottom of the Ge layer helps to increase the optical absorption efficiency to above 80...

We study the nano- and micro-structures that increase the optical efficiency of the CMOS image pixels in visible and infrared. We consider the difference between the micro-holes at the pixels’ bottom and the top and the holes that are composed of smaller holes. Those solutions can facilitate the fabrication. We study the crosstalk and the optical e...

3D simulations are conducted using Lumerical software to study the performance of surface illuminated silicon positive–intrinsic–negative photodiodes with microholes. Drift-diffusion equations are solved including the effects of carrier lifetime due to Shockley–Read–Hall and Auger recombination mechanisms, as well as high field mobility. Lumerical’...

Engineered spectral response in photodetectors combined with advanced signal processing and deep learning-based image reconstruction enables widespread applications of hyperspectral imaging. These advancements in spectral imaging eliminate the need for complex filters and dispersion lenses, benefiting various fields such as remote sensing, astronom...

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, surp...

Since the advent of impact ionization and its application in avalanche photodiodes (APD), numerous application goals have contributed to steady improvements over several decades. The characteristic high operating voltages and the need for thick absorber layers (π-layers) in the Si-APDs pose complicated design and operational challenges in complemen...

We study the nano- and micro-structures that increase the optical efficiency of the CMOS image pixels in visible and infrared. We consider the difference between the micro-holes at the pixels' bottom and the top and the holes that are composed of smaller holes. Those solutions can facilitate the fabrication. We study the crosstalk and the optical e...

We present a germanium “Ge-on-Si” CMOS image sensor with backside illumination for the near-infrared (NIR) electromagnetic waves (wavelength range 300 to 1700 nm) detection essential for optical sensor technology. The microholes help to enhance the optical efficiency and extend the range to the 1.7-μm wavelength. We demonstrate an optimization for...

Every bit of information that circulates the internet across the globe is a pulse of light, that at some point will need to be converted to an electric signal in order to be processed by the electronic circuitry in our data centers, computers, and cell phones. Photodetectors (PD’s) perform this conversion with ultra high speed and efficiency, in ad...

One-dimensional (1D) nanostructuresOne-dimensional (1D) nanostructures, including nanorodsNanorod, nanowiskers, nanowiresNanowire, nanotubes and nanobelts, have been receiving a great deal of research attention from industry and academia in recent years. Due to their special and outstanding many characteristics, such as effective light–trapping abi...

We present a Ge-on_Si CMOS image sensor with backside illumination for the near-infrared electromagnetic waves, wavelengths range 300-1700nm, detection essential for optical sensor technology. The micro-holes help to enhance the optical efficiency and extend the range to the 1.7 microns wavelength. We demonstrate an optimization for the width and d...

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...

Interest in the synthesis and fabrication of gallium oxide (Ga2O3) nanostructures as wide bandgap semiconductor-based ultraviolet (UV) photodetectors has recently increased due to their importance in cases of deep-UV photodetectors operating in high power/temperature conditions. Due to their unique properties, i.e., higher surface-to-volume ratio a...

Controlling light penetration depth in Avalanche Photodiodes (APDs) and Single Photon Avalanche Diodes (SPADs) play a major role in achieving high multiplication gain by delivering light near the multiplication region where the electric field is the strongest. Such control in the penetration depth for a particular wavelength of light has been previ...

Optical spectrometers are widely used scientific equipment with many applications involving material characterization, chemical analysis, disease diagnostics, surveillance, etc. Emerging applications in biomedical and communication fields have boosted the research in the miniaturization of spectrometers. Recently, reconstruction-based spectrometers...

The optimization of silicon photodiode-based CMOS sensors with backside-illumination for 300-1000 nm wavelength range was studied. It was demonstrated that a single hole on a photodiode increases the optical efficiency of the pixel in near-infrared wavelengths. A hole with optimal dimensions enhanced optical absorption by 60% for a 3 $\mu$m thick S...

The importance of Ga2O3-based material for harsh environmental applications has attracted the interest of researchers in exploring various fabrication and growth techniques of Ga2O3-based nanomaterials using effective and low-cost processes. Herein, a demonstration to improve the wettability of liquid gallium on a rough silicon surface is presented...

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 s...

Enhancing photon detection efficiency and time resolution in photodetectors in the entire visible range is critical to improve the image quality of time-of-flight (TOF)-based imaging systems and fluorescence lifetime imaging (FLIM). In this work, we evaluate the gain, detection efficiency, and timing performance of avalanche photodiodes (APD) with...

Enhancing photon detection efficiency and time resolution in photodetectors in the entire visible range is critical to improve the image quality of time-of-flight (TOF)-based imaging systems and fluorescence lifetime imaging (FLIM). In this work, we evaluate the gain, detection efficiency, and timing performance of avalanche photodiodes (APD) with...

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...

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 th...

Silicon photodetectors operating at near-infrared wavelengths with high-speed and high sensitivity are becoming critical for emerging applications, such as Light Detection and Ranging Systems (LIDAR), quantum communications, and medical imaging. However, such photodetectors present a bandwidth-absorption trade-off at those wavelengths that have lim...

In the last decade, interest in the use of beta gallium oxide (β-Ga2O3) as a semiconductor for high power/high temperature devices and deep-UV sensors has grown. Ga2O3 has an enormous band gap of 4.8eV, which makes it well suited for these applications. Compared to thin films, nanowires exhibit a higher surface-to-volume ratio, increasing their sen...

A simple and inexpensive thermal oxidation process was performed to synthesize gallium oxide (Ga2O3) nanowires using Ag thin film as a catalyst at 800 °C and 1000 °C to understand the effect of the silver catalyst on the nanowire growth. The effect of doping and orientation of the substrates on the growth of Ga2O3 nanowires on single-crystal galliu...

Silicon photodiode based CMOS sensors with backside-illumination for 300 to 1000 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 microns thick Si. It is 4x better than for the flat pixel. We comp...

Gallium oxide (Ga2O3) is a new wide bandgap semiconductor with remarkable properties that offers strong potential for applications in power electronics, optoelectronics, and devices for extreme conditions. In this work, we explore the morphology of Ga2O3 nanostructures on different substrates and temperatures. We used silver catalysts to enhance th...

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.

In recent years, interest in the use of gallium oxide (Ga2O3) in semiconductor devices has increased due to its wide bandgap that permits device operation at high temperatures and high voltages. As the size of these devices decrease, it becomes more important to be able to produce features on the micro and nanoscale. Traditional etching (both wet a...

Si Nanowires (NWs) are typically synthesized on limited substrates that lack essential characteristics, such as mechanical flexibility and optical transparency. Most of the synthesis processes are also costly and inhibit widespread applications enabled by NWs. Throughout this study, therefore, we have shown that ordered and disordered single crysta...

We investigated the effect of silver catalysts to enhance the growth of Ga2O3 nanowires. The growth of Ga2O3 nanowires on a P+-Si (100) substrate was demonstrated by using a thermal oxidation technique at high temperatures (~1000 ◦C) in the presence of a thin silver film that serves as a catalyst layer. We present the results of morphological, comp...

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.

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 wave...

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...

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 phot...

Single photon avalanche photodetectors (SPADs) can detect extremely low levels of light due to their improved signal-to-noise ratios compared to any other semiconductor photodetectors. This makes them attractive for applications such as long-range LIDAR that can ensure eye safety, biomedical imaging and other emerging applications. In this work, SP...

The performance of middle- and long-wavelength infrared (IR) detectors still limits to the dark current characteristics and associated noise behavior. In this work, we report reducing the noise caused by the dark current to ensure high operating temperature (HOT) of the IR detectors and improve the detector quantum efficiency (QE), by using a thin...

Light trapping in the near infrared wavelength (800-1800 nm) with nanohole array in silicon and germanium on silicon surface illuminated photodiodes (PD) , avalanche photodiodes (APD) and single photon avalanche photodiode (SPAD) enable absorption layers 5-10 times or more thinner than commercial Si PD/APD/SPAD. External quantum efficiency can be 1...

Etching in wide-bandgap semiconductors such as GaN aids applications including transistors, sensors, and radioisotope batteries. Plasma-based etching can induce surface damage and contamination that is detrimental to device performance. We present a photoelectrochemical approach to etching n-type GaN that is low-cost, simple, and environmentally be...

Magnetic quantum-dot cellular automata (MQCA) based computation started emerging as the Moore's law approaching towards its end. Number of nanomagnets and the area occupancy are major constraints in materializing this MQCA-based digital arithmetic circuit design. In this letter, we propose a design methodology and demonstrate the hybrid approach of...

Development of cost-effective and power-efficient optical interconnects is required to meet high demand of data transfer in the era of Internet of Things (IoT) that is expected to connect billions of sensors with different functionalities. The cost of optical links must be reduced for a wide adoption of optical interconnects in the fast data transm...

The implementation of ultra-thin and highly efficient photodetectors and photovoltaic devices is crucial to realize flexible and wearable products in the era of Internet of Things (IoT). CMOS-compatible processing and well-established manufacturing makes Silicon (Si) a great material of choice in many applications but thin crystalline-Si is not as...

The study proposes to use the photon trapping micro-structures to enhance quantum efficiency of the mid infrared photodetectors. The nanostructure that is consist of micro holes reduces reflection and bends the near normally incident light into the lateral modes in the absorbing layer.

The photon trapping nano-structures help to enhance quantum efficiency and reduce reflection for MSM photodetector that allows fast Si photodetectors at wavelength 800-950nm. The nanostructure consist of micro holes reduces reflection and bends normally incident light into the lateral modes in the absorbing layer.

We optimized micro-holes in a thin slab for fast Si photodetectors at wavelength 800-950nm. Lateral modes are shown to be responsible for the effective light trapping. Small disorder and cone hole shapes helped achieve uniform quantum efficiency in a wide wavelength range.

β-Ga2O3 thin films were grown on n-type GaN substrates using the sol–gel method. The forward-biased temperature dependent current–voltage (I–V–T) characteristics of Ni/β-Ga2O3/GaN structure have been investigated in the temperature range of 298–473 K. The apparent barrier height (\({\phi _{ap}}\)) increased while the ideality factor (n) decreased w...

In this paper, high-speed surface-illuminated Ge-on-Si pin photodiodes with improved efficiency are demonstrated. With photon-trapping microhole features, the external quantum efficiency (EQE) of the Ge-on-Si pin diode is >80% at 1300 nm and 73% at 1550 nm with an intrinsic Ge layer of only 2 μm thickness, showing much improvement compared to one w...

The papers included in this volume were part of the technical conference cited on the cover and title page. Papers were selected and subject to review by the editors and conference program committee. Some conference presentations may not be available for publication. The papers published in these proceedings reflect the work and thoughts of the aut...

In this paper, high speed surface-illuminated Ge-on-Si pin photodiodes with a broadband high efficiency are demonstrated. With photon-trapping microholes features, the external quantum efficiency (EQE) of the Ge-on-Si pin diode is >80% at 1300 nm and 73% at 1550 nm with only 2 µm thick intrinsic Ge layer, showing much improvement compared to the on...

Micro and nanoscale holes on the surfaces of indirect band gap semiconductors such as silicon can enable perpendicular light bending and trapping of photons to enhance the light material interactions and absorption by orders of magnitude. The ‘bending’ of a vertically oriented light beam at nearly 90 degrees can be visualized as radial waves genera...

Recently, a high-speed and high-efficiency silicon photodiode (PD) was demonstrated by enabling light trapping micro/nanostructured holes. While attractive for light manipulation, these high surface-to-volume-ratio nanostructures, which are created by top-down dry etching processes, can also bring other challenges, such as creating silicon surface...

In this study, indium-tin-zinc-oxide (ITZO) and Zn doped In2O3 nanowires were directly grown as bridged nanowires between two heavily doped silicon (Si) electrodes on an SOI wafer using single step vapor–solid–solid (VSS) growth method. SEM analysis showed highly dense and self aligned nanowire formation between the Si electrodes. Electrical and UV...

We demonstrate a silicon-based surface-illuminated CMOS-compatible broadband photodiode with ≤30ps FWHM and above 55% EQE at 850nm for up to 50Gb/s by using photontrapping micro/nano-structures. This is the fastest reported response for a Silicon photodiode.

Photo-electrochemical (PEC) etching can produce high-aspect ratio features, such as pillars and holes, with high anisotropy and selectivity, while avoiding the surface and sidewall damage caused by traditional deep reactive ion etching (DRIE) or inductively coupled plasma (ICP) RIE. Plasma-based techniques lead to the formation of dangling bonds, s...

A charge trap flash (CTF) memory based on AlGaN/GaN transistors has been proposed for memory development in high temperature environment. The proposed device is designed to have a positive threshold voltage for applying NAND or NOR arrays. In order to improve the electron storage ability at high temperature, various dielectrics have been applied. T...

We demonstrate a silicon-based surface-illuminated CMOS-compatible broadband photodiode with ≤30ps FWHM and above 55% EQE at 850nm for up to 50Gb/s by using photon-trapping micro/nano-structures. This is the fastest reported response for a Silicon photodiode.

Photodetectors (PDs) used in communication systems require ultrafast response, high efficiency, and low noise. PDs with such characteristics are increasingly in demand for data centers, metro data links, and long-haul optical networks. In a surface-illuminated PD, high speed and high efficiency are often a tradeoff, since a high-speed device needs...

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 in...

Micro- and nano scale pillars and holes with high aspect ratios for optoelectronic devices and sesnors can be fabricated by deep reactive ion etching (DRIE) or inductively coupled plasma (ICP) RIE. However, dry etching induced dam-ages to the sidewalls and the surfaces lead to the formation of dangling bonds, surface traps, car-rier leakage paths a...

The Si pin PDs at the short-reach multimode datacom wavelengths of 840–860 nm and at a short wavelength division multiplexing (SWDM) band of 850–950 nm could facilitate the integration [1] and reduce the cost. Our recent study [2] showed experimentally that a microstructure can increase the Si PDs quantum efficiency (QE) so that less than 2 micron...

The p-type Si nanowires were synthesized via deep reactive ion etching (DRIE). Al-doped ZnO films were coated on a p-Si nanowires substrate using the sol-gel method. Al-doped ZnO/p-Si NWs were characterized using current-voltage (I-V) and capacitance-voltage (C-V) measurements in the dark and under illumination at room temperature. Electrical param...

Surface-illuminated photodiodes (PDs) for ultra-fast data transmission are typically GaAs-based non-CMOS compatible detectors. Silicon (Si) has long been ignored for being a material of choice in ultra-fast communication links due to its poor responsivity for the wavelengths >800 nm at data rates 10 Gb/s or higher. Recent demonstration of CMOS comp...

Here (article No. 201700102), large-scale, thin films of β-Ga2O3 are prepared via the thermal oxidation of GaAs and removed via spontaneous delamination. These films have lateral dimensions at the centimeter scale, four orders of magnitude larger than previously reported literature results, and may be transferred to new substrates to overcome the l...

The Si pin PDs at the short-reach multimode datacom wavelengths of 840–860 nm and at a short wavelength division multiplexing (SWDM) band of 850–950 nm could facilitate the integration [1] and reduce the cost. Our recent study [2] showed experimentally that a microstructure can increase the Si PDs quantum efficiency (QE) so that less than 2 micron...

A very simple and inexpensive method for growing β-Ga2O3 films by heating GaAs wafers at high temperature in a furnace was found to contribute to large-area, high-quality β-Ga2O3 nanoscale thin films as well as nanowires depending on the growth conditions. We present the material characterization results including the optical band gap, Schottky bar...

We present a CMOS compatible fabrication technique to create micro/nanostructures on silicon and germanium surfaces for effective photon trapping and enhanced absorption. We achieved many times of absorption enhancement enabled by these photon trapping micro/nanostructures compared to bulk silicon and germanium counterparts. This method can lead to...