Avalanche Photodiodes Research Articles

High-speed and low dark current InGaAs/InAlAs avalanche photodiodes with P-type absorption layers

High-speed and low dark current InGaAs/InAlAs avalanche photodiodes with P-type absorption layers

Research on infrared image guided GM-APD range image recovery algorithm under limited detections

Geiger-mode avalanche photodiode (GM-APD) focal plane array lidar has a high photon-sensitive detection ability and can acquire three-dimensional(3D) distance information. However, high noise intensity and limited detections can easily lead to the loss of target pixels in the range image, and excellent signal extraction and noise suppression technology become crucial. To solve this problem, we propose a guided image recovery (GIR) method which first uses the infrared image information to recover the GM-APD range image. Unlike image fusion technology, which sacrifices the true range value or the objectively existing 3D range image to get the complete image, it cannot only recover the complete image but also guarantee the 3D image is true. The main innovation of the proposed algorithm is to search the missing pixels of the range image based on the boundary information of infrared images and extracts the range values from their own original measurement data according to the adjacent pixels’ information. According to Monte Carlo simulation and experimental data analysis, the proposed method has excellent target recovery, noise suppression, and fidelity performance under limited detections and low SBRs conditions, which provides an important reference for GM-APD lidar real-time detection. It also provides a new research direction for GM-APD lidar range image reconstruction.

Prediction of the Number of Cumulative Pulses Based on the Photon Statistical Entropy Evaluation in Photon-Counting LiDAR.

Photon-counting LiDAR encounters interference from background noise in remote target detection, and the statistical detection of the accumulation of multiple pulses is necessary to eliminate the uncertainty of responses from the Geiger-mode avalanche photodiode (Gm-APD). The cumulative number of statistical detections is difficult to select due to the lack of effective evaluation of the influence of the background noise. In this work, a statistical detection signal evaluation method based on photon statistical entropy (PSE) is proposed by developing the detection process of the Gm-APD as an information transmission model. A prediction model for estimating the number of cumulative pulses required for high-accuracy ranging with the background noise is then established. The simulation analysis shows that the proposed PSE is more sensitive to the noise compared with the signal-to-noise ratio evaluation, and a minimum PSE exists to ensure all the range detections with background noise are close to the true range with a low and stable range error. The experiments demonstrate that the prediction model provides a reliable estimation of the number of required cumulative pulses in various noise conditions. With the estimated number of cumulative pulses, when the signal photons are less than 0.1 per pulse, the range accuracy of 4.1 cm and 5.3 cm are obtained under the background noise of 7.6 MHz and 5.1 MHz, respectively.

High-Speed Waveguide-Integrated Avalanche Photodiodes for Near-Infrared Wavelengths on SiN-on-SOI Photonic Platform

Recently, there have been efforts on developing monolithically integrated avalanche photodiodes (APDs) for visible and near-infrared (NIR) wavelengths. However, the fabrication of these detectors in commercial photonic foundries often requires custom integration flow due to many design rule violations in standard integration process. This increases the fabrication cost, hinders the use of highly robust integration platform, and prevents access to well-mature process design kits. Here, we report on waveguide-integrated APDs operating at 850 nm by utilizing a commercial silicon nitride-on-silicon-on-insulator (SiN-on-SOI) photonics platform with no process modifications. Our devices comprise a SiN waveguide for input light routing and an SOI layer underneath to form APDs. We examine the effect of different junction parameters and device length on DC and high-speed device performance. We demonstrate high gain-bandwidth product up to 120 GHz with low dark current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{&lt; }$</tex-math></inline-formula> 25 nA and high responsivity that can reach 0.71 A/W, and observe open eye diagrams at up to 40 Gbps for all device variations. The performance parameters are on-par or even superior when compared to other integrated APDs operating in the NIR wavelengths. Being compatible with the standard integration flow of a multi-project wafer service of a commercial foundry, our devices are readily accessible, and they expand the functionalities of well-mature SiN-on-SOI photonics platform for applications ranging from optical interconnects, LIDAR, visible light communication to biosensing and quantum applications.

Investigation of Ga2O3/diamond heterostructure solar-blind avalanche photodiode via TCAD simulation

A Ga2O3/diamond separate absorption and multiplication avalanche photodiode (SAM-APD) with mesa structure has been proposed and simulated. The simulation is based on an optimized Ga2O3/diamond heterostructure TCAD physical model, which is revised by repeated comparison with the experimental data from the literature. Since both Ga2O3 and diamond are ultra-wide bandgap semiconductor materials, the Ga2O3/diamond SAM-APD shows good solar-blind detection ability, and the corresponding cutoff wavelength is about 263 nm. The doping distribution and the electric field distribution of the SAM-APD are discussed, and the simulation results show that the gain of the designed device can reach 5 × 104 and the peak responsivity can reach a value as high as 78 A/W.

Infrared detector module for airborne hyperspectral LiDAR: design and demonstration.

Realizing the integrated acquisition and identification of the elevation information and spectral information of the observation target is at the frontier and a future trend of Earth observation technology. This study designs and develops a set of airborne hyperspectral imaging lidar optical receiving systems and investigates the detection of the infrared band echo signal of the lidar system. A set of avalanche photodiode (APD) detectors is independently designed to detect the weak echo signal of 800-900nm band. The actual radius of the photosensitive surface of the APD detector is 0.25mm. We design and demonstrate the optical focusing system of the APD detector in the laboratory and obtain that the image plane size of the optical fiber end faces of the APD detector from channel 47 to channel 56 is close to 0.3mm. Results show that the optical focusing system of the self-designed APD detector is reliable. On the basis of the focal plane splitting technology of the fiber array, we couple the echo signal of 800-900nm band to the corresponding APD detector through the fiber array and conduct a series of test experiments for the APD detector. Field test results of the ground-based platform show that the APD detectors in all channels can complete the remote sensing measurement of 500m. The development of this APD detector solves the problem of hyperspectral imaging under weak light signals and realizes the accurate detection of ground targets in the infrared band by airborne hyperspectral imaging lidar.

Research on Quantitative Correlation between Performance and Structure Parameters Fluctuation of InGaAs(P)/InP Gm-APD

A statistics method is proposed to research the quantitative correlation between device performance and structure parameters fluctuation of avalanche photodiode (APD), through theoretical simulation and setting varied structure parameters. The characteristics of InGaAsP/InP APD and InGaAs/InP APD with the same primary structure parameters are discussed, and the quantitative correlation between excess bias fluctuation and structure parameters fluctuation of the two species APDs is concluded. It is revealed that the excess bias of APD is strongly determined by the doping of charge layer, the width of charge layer and multiplication layer, and it is slightly determined by the doping and the width of absorption layer. Moreover, the two species APDs have close response uniformity and technical stability at the same condition of material manufacture and device process.

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

Micropatterned Heterojunction Photodiodes In article number 2200636, Yusuke Adachi and Taizo Kobayashi developed micropatterned photodiodes using selenium thin films which exhibit high optical absorption at visible wavelengths. Ga2O3/Se heterojunction avalanche photodiodes are miniaturized to square-shaped micropatterns at 100 μm2. Photocurrent density is increased with decreasing the active area, and the highest external quantum efficiency of 330% is observed at a bias voltage of 15 V at the active area of 100 μm2.

High-gain low-excess-noise MWIR detection with a 3.5-µm cutoff AlInAsSb-based separate absorption, charge, and multiplication avalanche photodiode

Mid-wavelength infrared (MWIR) detection is useful in a variety of scientific and military applications. Avalanche photodiodes can provide an advantage for detection as their internal gain mechanism can increase the system signal-to-noise ratio of a receiver. We demonstrate a separate absorption, charge, and multiplication avalanche photodiode using a digitally grown narrow-bandgap Al0.05InAsSb absorber for MWIR detection and a wide bandgap Al0.7InAsSb multiplier for low-excess-noise amplification. Under 2-µm illumination at 100 K, the device can reach gains over 850. The excess noise factor of the device scales with a low k-factor of ∼0.04. The unity-gain external quantum efficiency of the device attains a peak of 54% (1.02 A/W) at 2.35 µm and maintains an efficiency of 24% (0.58 A/W) at 3 µm before cutting off at ∼3.5 µm. At a gain of 850, the device has a gain-normalized dark current density of 0.05 mA/cm2. This device achieves gains more than double that of the state-of-the-art InAs detectors and achieves gain-normalized dark current densities over two orders of magnitude lower than that of a previously reported MWIR Al0.15InAsSb-based detector.

All-silicon microring avalanche photodiodes with a >65 A/W response.

We report an all-Si microring (MRR) avalanche photodiode (APD) with an ultrahigh responsivity (R) of 65 A/W, dark current of 6.5 µA, and record gain-bandwidth product (GBP) of 798 GHz at -7.36 V. The mechanisms for the high responsivity have been modelled and investigated. Furthermore, open eye diagrams up to 20 Gb/s are supported at 1310 nm at -7.36 V. The device is the first, to the best of our knowledge, low cost all-Si APD that has potential to compete with current commercial Ge- and III-V-based photodetectors (PDs). This shows the potential to make the all-Si APD a standard "black-box" component in Si photonics CMOS foundry platform component libraries.

Guard Ring Design to Prevent Edge Breakdown in Double-Diffused Planar InGaAs/InP Avalanche Photodiodes

We report on the design of an attached guard ring (AGR) and a floating guard ring (FGR) in a planar separate absorption, grading, charge, and multiplication In0.53Ga0.47As/InP avalanche photodiode to prevent premature edge breakdowns. The depths of the two Zn diffusions were utilized to manipulate the guard ring structures. Results from TCAD simulation indicate that the optimal AGR diffusion depth is right at the turning point where the breakdown current shifts from the edge of active region to the AGR region. The devices with optimal AGR depth contain significantly higher breakdown voltages than those of devices either with shallower-or without any- AGR. For the FGR design, a series of devices with different spacings between AGR and FGR and different FGR opening widths for diffusion were fabricated and characterized. We show that when the spacing is longer than the critical value, the breakdown voltage can increase ~1.5 V higher than those of the APD devices without FGR. In addition, the wider the FGR opening width, the higher the breakdown voltage. TCAD simulations were also performed to study the effect of FGR, but showed less pronounced improvements, which could be due the discrepancy between the calculated and experimental diffusion profile.

Ultra-narrowband interference circuits enable low-noise and high-rate photon counting for InGaAs/InP avalanche photodiodes.

Afterpulsing noise in InGaAs/InP single photon avalanche photodiodes (APDs) is caused by carrier trapping and can be suppressed successfully through limiting the avalanche charge via sub-nanosecond gating. Detection of faint avalanches requires an electronic circuit that is able to effectively remove the gate-induced capacitive response while keeping photon signals intact. Here we demonstrate a novel ultra-narrowband interference circuit (UNIC) that can reject the capacitive response by up to 80 dB per stage with little distortion to avalanche signals. Cascading two UNIC's in a readout circuit, we were able to enable a high count rate of up to 700 MC/s and a low afterpulsing of 0.5 % at a detection efficiency of 25.3 % for 1.25 GHz sinusoidally gated InGaAs/InP APDs. At a temperature of -30 ∘C, we measured an afterpulsing probability of 1 % at a detection efficiency of 21.2 %.

Free-Running Single-Photon Detection via GHz Gated InGaAs/InP APD for High Time Resolution and Count Rate up to 500 Mcount/s

Free-running InGaAs/InP single-photon avalanche photodiodes (SPADs) typically operate in the active-quenching mode, facing the problems of long dead time and large timing jitter. In this paper, we demonstrate a 1-GHz gated InGaAs/InP SPAD with the sinusoidal gating signals asynchronous to the incident pulsed laser, enabling free-running single-photon detection. The photon-induced avalanche signals are quenched within 1 ns, efficiently reducing the SPAD's dead time and achieving a count rate of up to 500 Mcount/s. However, the timing jitter is measured to be ~168 ps, much larger than that of the SPAD with synchronous gates. We adjust the delay between the gating signals and the incident pulsed laser to simulate the random arrival of the photons, and record the timing jitter, respectively, to figure out the cause of the jitter deterioration. In addition, the effects of the incident laser power and working temperature of the APD on the time resolution have been investigated, broadening the applications of the GHz gated free-running SPAD in laser ranging and imaging, fluorescence spectroscopy detection and optical time-domain reflectometry.

Review of Ge(GeSn) and InGaAs Avalanche Diodes Operating in the SWIR Spectral Region.

Among photodetectors, avalanche photodiodes (APDs) have an important place due to their excellent sensitivity to light. APDs transform photons into electrons and then multiply the electrons, leading to an amplified photocurrent. APDs are promising for faint light detection owing to this outstanding advantage, which will boost LiDAR applications. Although Si APDs have already been commercialized, their spectral region is very limited in many applications. Therefore, it is urgently demanded that the spectral region APDs be extended to the short-wavelength infrared (SWIR) region, which means better atmospheric transmission, a lower solar radiation background, a higher laser eye safety threshold, etc. Up until now, both Ge (GeSn) and InGaAs were employed as the SWIR absorbers. The aim of this review article is to provide a full understanding of Ge(GeSn) and InGaAs for PDs, with a focus on APD operation in the SWIR spectral region, which can be integrated onto the Si platform and is potentially compatible with CMOS technology.

Suppressing the influence of GM-APD coherent lidar saturation by signal modulation

Geiger-mode Avalanche Photo Diode (GM-APD) coherent lidar improves coherent detection sensitivity to single photon level, which is more suitable for remote target detection. However, due to the limited pixels, the photon count will be affected by the system saturation, resulting in low utilization of local oscillator (LO), reducing the system's signal-to-noise ratio (SNR). A GM-APD coherent lidar system based on signal modulation is proposed, the method uses an electro-optic modulator to modulate the slope of signal light, then GM-APD coherent detection. Firstly, the detection and optimal parameter model based on signal modulation are derived. Secondly, the effectiveness of this system is analyzed through simulation. Finally, GM-APD coherent detection experiment based on signal modulation is carried out to verify the effectiveness of the system. When the echo position is 2 μs, the pulse width is 200 ns, the number of signal photons is about 8000, LO photons is about 820, signal modulation improves the system SNR by more than two times. It is concluded that the greater influence of saturation on GM-APD coherent lidar, the better signal modulation effect. The proposed scheme improves the utilization rate of LO and SNR from equipment level, to further enhance system detection ability.

High-Performance Cascaded Surface-Illuminated Ge-on-Si APD Array

In this letter, we report a cascaded surface-illuminated Germanium-on-Silicon (Ge-on-Si) avalanche photodiode (APD) array with a low dark current. The photodetector array cascades seven Ge-on-Si APDs through interconnecting the charge regions to form photomultiplier tubesiPMTjC which increases the effective light absorption area compared to the single APD scheme. To the best of our knowledge, this is the first time that Ge-on-Si PMT has been reported. The optimum response of single-electrode (2 pixels) Ge-on-Si APD is 2.4 A/W with a dark current of 100 nA, and the optimum bandwidth is 52 MHz. PMT has a responsivity of approximately 3 times that of a single-electrode Ge-on-Si APD for the same dark current (100 nA). With low dark current, our PMT has a better optical amplification effect than the parallel Ge-on-Si PD. We have also further tested the current tuning properties of the Ge-on-Si APD arrays with different applied Ge voltages. The test demonstrates the feasibility of cascading three-electrode APD arrays. A cascaded Ge-on-Si APD array with good photodetection properties at low-light conditions has been demonstrated which provides guidance for the design of large-scale Ge-on-Si APD arrays for light detection and ranging application.

Characteristics Measurement in a Deep UV Single Photon Detector Based on a TE-cooled 4H-SiC APD

We report on the characteristics of a lab-assembled UV single photon detector based on a thermoelectrically cooled silicon carbide (4H-SiC) avalanche photodiode (APD). The SiC- APD in this experiment was fabricated with a beveled mesa structure, with electronics designed to achieve passive Geiger-mode operation and to convert the avalanche signal to a transistor–transistor logic signal by readout backend. We attached the SiC-APD to a 4-stage thermoelectric cooler to vary APD temperature from 25 °C to −30 °C, and investigated dark count rates according to applied bias voltage at different temperatures. Breakdown voltages applied to the SiC-APD were also measured while adjusting APD temperature. Finally, we evaluated afterpulse characteristics through the time-correlated single-photon counting method, and observed that afterpulsing probability increases with decreasing APD temperature.

Resonant InGaAs Detectors and Emitters for Passive and Active Imaging Application

In this work, we design an InGaAs avalanche photodiode (APD) with a higher photocurrent to dark current ratio than a conventional APD. The improvement is based on optical confinement in an optical resonator, which increases the optical intensity in the detector volume and thus its quantum efficiency. With optical confinement, the absorbing layer can be 20 times thinner than the conventional APD, reducing the intrinsic generation-recombination dark current by the same amount and still be able to produce 90.9% of the photocurrent. The photocurrent to intrinsic dark current ratio can thus be increased theoretically by 18.2 times in concomitant with a lower operating voltage. Higher photocurrent can also be obtained using a thicker absorber. Besides APDs, the optical resonator structure can also be applied to p-i-n photodiodes for similar improvement. To further increase the detection sensitivity, we design an efficient InGaAsP light emitting diode (LED) having a similar resonator geometry. The resonator geometry enables more collimated emission and increases the optical power theoretically by more than 36 times compared to a conventional LED. Integrating the resonant APD and LED together will yield a powerful SWIR transceiver for various low light, LIDAR, and 3-dimensional imaging applications.

SECALROC2: A Low-Noise, High-Speed, and Full Digital Outputs Front-End ASIC for STCF Electromagnetic Calorimeter With APD Detectors

In this work, a low-noise and high-rate front-end readout application-specific integrated circuit (ASIC) named SECALROC2 for the electromagnetic calorimeter (ECAL) in the super tau-charm factory (STCF) is presented. The chip is designed to process signals generated from avalanche photodiode detectors (APDs) for both energy and time measurement. The large detector capacitance and leakage current of the APD pose a great challenge to the noise and speed performance of the front-end readout circuit (ROC). A low-noise preamplifier and a fifth-order high-linearity shaper with adjustable peaking times are proposed to decrease noise induced by the 270-pF detector capacitance. A peak detect-and-hold circuit and a high-linearity differential analog buffer are adopted to convert each peak voltage of the shaper to differential voltages with sufficient driving capability. A fast shaper and a discriminator are implemented to produce trigger signals for the time of arrival (TOA) measurement. To reduce the complexity and power consumption of the ECAL system, a 12-bit 10-MS/s pipelined analog-to-digital converter (ADC) and a 16-bit three-stage time-to-digital converter (TDC) with 42-ps bin size TDC are integrated on-chip for full-digitalized outputs. This ASIC was designed and fabricated in a standard commercial 1P6M 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> mixed-signal CMOS process and the chip area occupancy is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.4\times1.6$ </tex-math></inline-formula> mm2. The experimental results show that the input charge of the ASIC ranges from 3.2 to 400 fC. The measured nonlinear error of the system is less than 2.5% with an event rate up to 400 kcps. The equivalent noise charge (ENC) is 1367 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{e}^{-}$ </tex-math></inline-formula> + 4.93 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{e}^{-}$ </tex-math></inline-formula> /pF at 800-ns peaking time. The timing resolution is better than 540 ps at an input charge of 160 fC. The measured ENC can achieve 3820 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{e}^{-}$ </tex-math></inline-formula> when the ASIC is connected to an APD detector. The effective number of bits (ENOB) of the ADC is 10.8-bit when operated at 10 MS/s.

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.