Avalanche Photodiodes Research Articles

Mechanisms of enhanced sub-bandgap absorption in high-speed all-silicon avalanche photodiodes

All-silicon (Si) photodiodes have drawn significant interest due to their single and simple material system and perfect compatibility with complementary metal-oxide semiconductor photonics. With the help from a cavity enhancement effect, many of these photodiodes have shown considerably high responsivity at telecommunication wavelengths such as 1310 nm, yet the mechanisms for such high responsivity remain unexplained. In this work, an all-Si microring is studied systematically as a photodiode to unfold the various absorption mechanisms. At − 6.4 V , the microring exhibits responsivity up to ∼ 0.53 A / W with avalanche gain, a 3 dB bandwidth of ∼ 25.5 GHz , and open-eye diagrams up to 100 Gb/s. The measured results reveal the hybrid absorption mechanisms inside the device. A comprehensive model is reported to describe its working principle, which can guide future designs and make the all-Si microring photodiode a promising building block in Si photonics.

Radiation hardness of a wide spectral range SiPM with quasi-spherical junction

New pixel geometries are on the rise to achieve high sensitivity in near-infrared wavelengths with silicon photomultipliers (SiPMs). We test prototypes of the tip avalanche photo-diodes, which feature a quasi-spherical p-n junction and a high photodetection efficiency over a wide spectral range, and analyze the performance after neutron irradiation. The observed increase in dark count rate is significantly smaller than for a SiPM with a conventional design, indicating a good radiation hardness of the pixel geometry.

Simultaneous single-particle tracking and fluorescence lifetime measurement with a single-photon detector array.

Fluorescence single-particle tracking (SPT) techniques are a fundamental tool for providing information on the complex functions and interactions of individual particles in biological environments. The main concern about following single particles resides mostly in how to make registered photons informative and the solution is usually optimized only to better extrapolate either the temporal or the spatial information. This tradeoff ultimately reflects into the contraposition of wide-field camera-based techniques and real-time SMT, with the latter representing the state of the art, but at the cost of high technical complexity. Furthermore, fluorescence lifetime information, despite being accessible in many cases, has yet to be measured consistently. Within the context of the BrightEyes ERC-2018-COG project, we present a real-time three-dimensional SPT implementation based on a confocal laser-scanning microscope featuring a 5×5 single-photon avalanche photodiode (SPAD) array detector capable of overcoming the above limitations due to an hybrid approach. Briefly, each sensitive element of the detector acts as a confocal pinhole, and the recorded intensity distribution mirrors the position of the particle with respect to the center of the excitation volume. The estimation is then used as input for a real-time feedback tracking system. Notably, each pixel is an independent photon counting detector, allowing for concurrent measurement of the fluorescence lifetime. The system is capable of experimentally tracking single particles with localization precision up to 30 nm with 100 photons and microsecond time resolution. The same photon stream is used to perform fluorescence lifetime measurements. The technique has been validated by tracking 20 nm fluorescent beads moved along a predetermined path and by measuring the diffusion coefficient when freely diffusing in water-glycerol solutions. As application, the movement of lysosomes in living cells has been investigated while assessing the lifetime of the GFP marker.

Extremely low excess noise avalanche photodiode with GaAsSb absorption region and AlGaAsSb avalanche region

An extremely low noise Separate Absorption and Multiplication Avalanche Photodiode (SAM-APD), consisting of a GaAs0.52Sb0.48 absorption region and an Al0.85Ga0.15As0.56Sb0.44 avalanche region, is reported. The device incorporated an appropriate doping profile to suppress tunneling current from the absorption region, achieving a large avalanche gain, ∼130 at room temperature. It exhibits extremely low excess noise factors of 1.52 and 2.48 at the gain of 10 and 20, respectively. At the gain of 20, our measured excess noise factor of 2.48 is more than three times lower than that in the commercial InGaAs/InP SAM-APD. These results are corroborated by a Simple Monte Carlo simulation. Our results demonstrate the potential of low excess noise performance from GaAs0.52Sb0.48/Al0.85Ga0.15As0.56Sb0.44 avalanche photodiodes.

Formation of Micro‐Patterned Ga2O3/Se Heterojunction and its Application to Highly Sensitive Avalanche Photodiode

Herein, the formation of square‐shaped micropatterns of a Ga2O3/Se heterojunction avalanche photodiode (APD) at an active area of 10 μm × 10 μm and its application to a visible light sensor with high sensitivity by amplification of photocurrent density for the first time are reported. The miniaturization of the Ga2O3/Se APD improves its signal‐to‐noise ratio (SNR) by 10 dB as compared to the expected SNR. This is possible because of the improvement in thermal radiation and reduction in resistance loss. The effects of scaling on the photovoltaic conversion characteristics of Ga2O3/Se and TiO2/Se are investigated by varying the active area from 100 μm × 100 μm to 10 μm × 10 μm using photolithography and etching. A remarkable increase in the external quantum efficiency is observed for miniaturized Ga2O3/Se heterojunction APD at widths smaller than 50 μm × 50 μm by a combination of avalanche amplification and the micro‐scaling effect at a bias voltage of 15 V.

High gain, low noise 1550 nm GaAsSb/AlGaAsSb avalanche photodiodes

High sensitivity avalanche photodiodes (APDs) operating at eye-safe infrared wavelengths (1400–1650 nm) are essential components in many communications and sensing systems. We report the demonstration of a room temperature, ultrahigh gain ( M = 278 , λ = 1550 n m , V = 69.5 V , T = 296 K ) linear mode APD on an InP substrate using a G a A s 0.5 S b 0.5 / A l 0.85 G a 0.15 A s 0.56 S b 0.44 separate absorption, charge, and multiplication (SACM) heterostructure. This represents ∼ 10 × gain improvement ( M = 278 ) over commercial, state-of-the-art InGaAs/InP-based APDs ( M ∼ 30 ) operating at 1550 nm. The excess noise factor is extremely low ( F < 3 ) at M = 70 , which is even lower than Si APDs. This design gives a quantum efficiency of 5935.3% at maximum gain. This SACM APD also shows an extremely low temperature breakdown sensitivity ( C b d ) of ∼ 11.83 m V / K , which is ∼ 10 × lower than equivalent InGaAs/InP commercial APDs. These major improvements in APD performance are likely to lead to their wide adoption in many photon-starved applications.

Avalanche photodiode detection system enables X-ray communication up to 10 Mbps

As the core part of the X-ray communication (XCOM) system, the X-ray detector directly affects the data rate and bit error ratio (BER) performance. An avalanche photodiode (APD) with fast response time and high intern gain is chosen as the detector sensor to improve the data rate of XCOM. A three-stage fast preamplifier using radio frequency amplifier chips is designed to amplify the weak signal from the APD sensor. The bit synchronization signal acquisition and signal judgment modules are established to demodulate the detected pulse X-ray signals. The single photon pulse response and signal-to-noise ratio characteristic of the APD detector are tested. The pulse response width is only 25 ns. The BER characteristic with 211,709-bit pseudo-random sequence and the eye diagram of the XCOM system based on the developed APD detector are evaluated. Results show that the BER is zero at the data rate lower than 6 Mbps and reaches 1.98 × 10−4 at 10 Mbps under 55 kV anode voltage, 1.58 A filament current, and a 10 cm air channel. The designed APD detector increases the data rate of XCOM from the level of 1 Mbps to 10 Mbps, indicating its potential application for a higher data rate.

3D reconstruction of the dynamic scene with high-speed targets for GM-APD LiDAR

With the advantages of high distance resolution, long detection distance, small size, and low power consumption, Geiger-mode avalanche photodiode (GM-APD) light detection and ranging (LiDAR) has excellent potential for applications such as three-dimensional earth mapping and autonomous driving. The reconstruction for GM-APD LiDAR is based on the statistics of multiple-laser-pulse data, leading to a long imaging time. There are problems such as blurring when the targets are high-speed, which limits its application scope. A reconstruction algorithm of the dynamic scene for GM-APD LiDAR is proposed in this paper to address this problem. Firstly, the motion features (such as velocity and position) of the targets in the scene are extracted by applying the Hough transform and used as a basis to isolate the targets’ echo from the background noise, significantly reducing the noise interference. With these features, the data are corrected for the spatial location to attenuate or eliminate the effects caused by the targets’ motion. Finally, the reconstruction is completed utilizing parameter estimation. Also, we discuss the super-resolution reconstruction capability of this algorithm with sufficient data. Reconstruction results of the scene with targets moving at 100–300 m/s are demonstrated at last. Compared to the conventional algorithms, the peak signal-to-noise ratio (PSNR) is improved by 3–4 dB, and the root-mean-square error (RMSE) of distance is improved by 6–10 times. In addition to a super-resolution reconstruction of the dynamic scene, this method also enables the detection, motion feature extraction, and position prediction of high-speed moving targets in the scene, significantly expanding the application scope of GM-APD LiDAR and having good practical application value.

Structural design of dual carrier multiplication avalanche photodiodes on InP substrate

Avalanche photodiodes are widely used in various fields, such as optical communication and laser radar, because of their high multiplication. In order to adapt to very weak signal detection applications, devices are required to have higher gain values. The existing avalanche photodiodes generally use single carrier multiplication mode of operation, its multiplication effect is limited. In this paper is designed an InP/In<sub>0.53</sub>Ga<sub>0.47</sub>As/In<sub>0.52</sub>Al<sub>0.48</sub>As avalanche photodiode structure with electrons and holes jointly involved in multiplication. In this structure, In<sub>0.53</sub>Ga<sub>0.47</sub>As material is used for the absorption layer, InP material is used for the hole multiplication layer, In<sub>0.52</sub>Al<sub>0.48</sub>As is used for the electron multiplication layer, and the two multiplication layers are distributed on the upper side and lower side of the absorber layer. Under the reverse bias, the photogenerated electrons and the absorber-layer generated holes can enter into the respective multiplier layers in different directions and create the avalanche multiplication effect, so that the carriers are fully utilized. This structure and the conventional single multiplication layer structure are simulated by Silvaco TCAD software. Comparing the single InP multiplication layer structure with the single In<sub>0.52</sub>Al<sub>0.48</sub>As multiplication layer structure, the gain value of the double multiplication layer structure at 95% breakdown voltage is about 2.3 times and about 2 times of the former two, respectively, and the device has a larger gain value because both carriers are involved in multiplication in both multiplication layers at the same time. The structure has a dark current of 1.5 nA at 95% breakdown voltage, which does not increase in comparison with the single multiplication layer structure, owing to the effective control of the electric field inside the structure by multiple charge layers. Therefore, this structure is expected to improve the detection sensitivity of the system.

Waving Effect Characterization for Water-to-Air Optical Wireless Communication

In this paper, we establish and experimentally verify a water-to-air (W2A) visible light communication (VLC) system through dynamic air-water interface. Considering the complexity of waves in real environments, we divide waves into largescale wave and small-scale wave. Monte Carlo simulation and experimental results show that small-scale wave mainly affects the energy distribution of the light spot on the receiving plane and the variation frequency of link gain, while largescale wave mainly affects the coverage of the light spot. In the W2A-VLC system based on light-emitting diode (LED), the statistical characteristics of variation time and link gain are mainly related to the small-scale wave, and the effect of large-scale wave can be treated as slow fading. In order to design a reliable communication system, a large-divergence-angle LED array and avalanche photodiode (APD) array are used under dynamic water surface. We investigate three cases, namely single-input multiple-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO). In the SIMO or MISO systems, the correlation coefficient of channel gain decreases with the inter-receiver or inter-transmitter distance. A significant transmission performance enhancement can be achieved by deploying more transmitters or receivers and increasing the distance between the transmitters or receivers. A MIMO structure can effectively increase the achievable rate. We further establish a W2A-VLC link in a deep wave pool to verify our research in the real environment. The results show that more intensive small-scale wave yields higher bit error rate (BER), and the diversity scheme can improve the transmission stability and decrease BER.

Compact InGaAs/InP Single-Photon Detector Module with Ultra-Narrowband Interference Circuits

Gated InGaAs/InP avalanche photodiodes are the most practical device for detection of telecom single photons arriving at regular intervals. Here, we report the development of a compact single-photon detector (SPD) module measured just 8.8 × 6 × 2 cm 3 in size and fully integrated with driving signal generation, faint avalanche readout, and discrimination circuits as well as temperature regulation and compensation. The readout circuit employs our previously reported ultra-narrowband interference circuits (UNICs) to eliminate the capacitive response to the gating signal. We characterize a UNIC-SPD module with a 1.25-GHz clock input and find its performance comparable to its counterpart built upon discrete functional blocks. Setting its detection efficiency to 30% for 1,550-nm photons, we obtain an afterpulsing probability of 2.4% and a dark count probability of 8 × 10 −7 per gate under 3-ns hold-off time. We believe that UNIC-SPDs will be useful in important applications such as quantum key distribution.

Error Analysis of Free Space Communication System Using Machine Learning

Free space optical (FSO) communication offers huge bandwidth, license-free spectrum and a more secure channel. PIN diodes are normally used for detection, but avalanche photodiodes (APD) are preferred for detecting high-speed FSO signals in many applications. In the case of APD, the noise distribution is input-dependent Gaussian noise (IDGN) rather than input-independent Gaussian noise (IIGN). We investigate the error analysis using on-off keying (OOK) for various detection approaches. This paper proposes a machine learning approach and compares its performance with soft and hard decisions. Soft values in the case of IDGN and IIGN are derived, and the optimum and sub-optimum detection thresholds are evaluated. The proposed novel ML approach shows better performance gains than the other approaches. It is also demonstrated that the IDGN model should have an optimum detection and achieve a gain of 2.5[dB] and about 1[dB] at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> = 0[dB] and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> = 10[dB], respectively. Experimental results are plotted for the FSO channel data, and a model fit curve is plotted using the ML approach.

High-uniformity 2 × 64 silicon avalanche photodiode arrays with silicon multiple epitaxy technology

In this paper, high-uniformity 2×64 silicon avalanche photodiode (APD) arrays are reported. Silicon multiple epitaxy technology was used, and the high performance APD arrays based on double-layer epiwafers are achieved for the first time, to the best of our knowledge. A high-uniformity breakdown voltage with a fluctuation of smaller than 3.5 V is obtained for the fabricated APD arrays. The dark currents are below 90 pA for all 128 pixels at unity gain voltage. The pixels in the APD arrays show a gain factor of larger than 300 and a peak responsivity of 0.53 A/W@M = 1 at 850 nm (corresponding to maximum external quantum efficiency of 81%) at room temperature. Quick optical pulse response time was measured, and a corresponding cutoff frequency up to 100 MHz was obtained.

High-stability 4H-SiC avalanche photodiodes for UV detection at high temperatures

In this work, high-stability 4H-SiC avalanche photodiodes (APDs) for ultraviolet (UV) detection at high temperatures are fabricated and investigated. With the temperature increasing from room temperature to 150°C, a very small temperature coefficient of 7.4 mV/°C is achieved for the avalanche breakdown voltage of devices. For the first time, the stability of 4H-SiC APDs is verified based on an accelerated aging test with harsh stress conditions. Three different stress conditions are selected with the temperatures and reverse currents of 175°C/100 µA, 200°C/100 µA, and 200°C/500 µA, respectively. The results show that our 4H-SiC APD exhibits robust high-temperature performance and can even endure more than 120 hours at the harsh aging condition of 200°C/500 µA, which indicates that 4H-SiC APDs are very stable and reliable for applications at high temperatures.

MOEMS-based Lens-Assisted Beam Steering for Free-Space Optical Communications

Free-space optical communication (FSOC) systems require precise pointing, acquisition, and tracking to send and receive optical beams for effective operation. In a lens-assisted beam steering (LABS) system, light is steered by controlling the emission location in a focal plane. The emitted light is directed into the scene by a lens, like a camera but operating in reverse. In this paper, we demonstrate a novel free-space optical communication link using a micro-opto-electro-mechanical-system (MOEMS) based photonic integrated circuit (PIC) for LABS between multiple receive locations. The MOEMS PIC operates via selective electrical actuation of an array of small grating switches (30 µm x 30 µm footprint, 100 µm pitch). Data rates up to 10 Gbps and a 3 dB optical bandwidth covering the infrared C and L bands (1530 nm to 1625 nm) are measured over a 1 m free-space link distance. Eye diagrams indicate a quality communication link for data rates up to 10 Gbps and bit-error-rates < 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> are measured for on-off keying (OOK) modulation. A measured beam profile is propagated into the far-field via simulation, and used to calculate link budgets for example CubeSat crosslink and downlink scenarios. Link budget calculations indicate potential > 1 Gbps CubeSat FSOC crosslinks for link lengths > 1000 km and 1 W of input optical power, using identical 90 mm transmit and receive apertures and a commercially-available fiber-coupled InGaAs avalanche photodiode (APD) receive detector.

SiC UV Avalanche Photodiode with High Voltage Withstanding Capability and Low Dark Count Rate

SiC UV Avalanche Photodiode with High Voltage Withstanding Capability and Low Dark Count Rate

Linear-mode HgCdTe avalanche photodiode detectors for photon-counting applications (invited)

Linear-mode HgCdTe avalanche photodiode detectors for photon-counting applications (invited)

Highly Sensitive InGaAs/InAlAs X-Ray Avalanche Photodiodes With Fast Time Response

Highly sensitive and fast responsive X-ray detectors are crucial for safety, accuracy, and stability in medical diagnosis. To achieve high sensitivity, the thick absorption layer is used to guarantee efficient X-ray photon absorption. However, there is a significant issue that the time response of photodetectors is sacrificed for a thick absorption layer. Herein, we demonstrate the possibility to use InGaAs/InAlAs separate absorption, grading, charge, and multiplication avalanche photodiodes (SAGCM APDs) for highly sensitive X-ray detection with fast time response. Thanks to the internal multiplication, the sensitivity of the optimized device is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.1\times 10^{5}\,\,\mu $ </tex-math></inline-formula> CGy−1 cm−2 under 50 keV hard X-ray radiation, which is 14000 times higher than commercial <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> -Se detectors. The 3-dB bandwidth of the APDs is 2.93 GHz, corresponding to a time response of 0.34 ns. To overcome the trade-off between sensitivity and time response, we propose a parameter named sensitivity-bandwidth product (SBP) to assess the system performance of the X-ray detector. The device exhibits a higher SBP ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.08\times 10^{5}\,\,\mu \text{C}\,\,\cdot $ </tex-math></inline-formula> GHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> Gy <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-1}\,\,\cdot $ </tex-math></inline-formula> cm−2) than any other reported X-ray detector. Our results may provide new strategies to develop a high-performance X-ray detector in medical diagnosis.

InGaAs/InAlAs single photon avalanche photodiodes for X-ray detection

InGaAs/InAlAs single photon avalanche photodiodes for X-ray detection

Accuracy of Tissue Oxygen Saturation Measurements of a Textile-Based NIRS Sensor.

Pressure injuries (PI) are dangerous tissue lesions that heal very slowly and pose a high risk of serious infections. They are caused by pressure applied to the tissue, which stops blood circulation and therefore induces hypoxia, i.e., low tissue oxygen saturation (StO2). PI cause severe suffering and are expensive to treat. Hence it is essential to prevent them with a device that detects a dangerous situation, e.g., by measuring StO2 using near-infrared spectroscopy (NIRS). For such a device to be wearable without causing PI, it must not introduce pressure points itself. This can be achieved by integrating optical fibers into a textile to transport light to and from the tissue.The aim of this paper is to investigate the accuracy of StO2 measurements using a NIRS device based only on textile-integrated optical fibers.Bundles of fibers were stitched into a textile in such a way that loops of <1 mm diameters were formed at the stitching locations. Detection points (DPs) on the fabric consisted of 8 fibers with 3 loops each. Emission points (EPs) were made from 4 fibers with 3 loops each. All fiber ends of a DP were connected to an avalanche photodiode. One end of each fiber belonging to an EP was connected to an LED (740nm, 810nm, or 880nm; 290, 560, or 610mW).To verify the accuracy of this textile-based sensor, we placed it on a subject's forearm and compared the derived StO2 during arterial occlusion to the values of a gold-standard NIRS device (ISS Imagent), which was placed on the forearm too.We found that our textile-based sensor repeatedly measured StO2 values over a range of 40% with a deviation of <10% from the reference device.By showing the ability to measure StO2 using textile-integrated optical fibers accurately, we have reached a significant milestone on our way to building a wearable device to monitor tissue health and prevent PI.