Analysis of high-temperature performance of 4H-SiC avalanche photodiodes in both linear and Geiger modes

The high-temperature performance of 4H-SiC ultraviolet avalanche photodiodes(APDs)in both linear and Geiger modes is extensively investigated.During the temperature-dependent measurements,a fixed bias voltage is adopted for the device samples,which is much more practical and important for high-temperature applications.The results show that the fabricated 4H-SiC APDs are very stable and reliable at high temperatures.As the temperature increases from room temperature to 425 K,the dark current at 95%of the breakdown voltage increases slightly and remains lower than40 pA.In Geiger mode,our 4H-SiC APDs can be self-quenched in a passive-quenching circuit,which is expected for highspeed detection systems.Moreover,an interesting phenomenon is observed for the first time:the single-photon detection efficiency shows a non-monotonic variation as a function of temperature.The physical mechanism of the variation in hightemperature performance is further analyzed.The results in this work can provide a fundamental reference for researchers in the field of 4H-SiC APD ultraviolet detectors.

Planar InAlAs/InGaAs avalanche photodiode with 360 GHz gain×bandwidth product

This paper describes a guardring-free planar InAlAs/InGaAs avalanche photodiode(APD)by computational simulations and experimental results.The APD adopts the structure of separate absorption,charge,and multiplication(SACM)with top-illuminated.Computational simulations demonstrate how edge breakdown effect is suppressed in the guardringfree structure.The fabricated APD experiment results show that it can obtain a very low dark current while achieving a high gain×bandwidth(GB)product.The dark current is 3 nA at 0.9Vb r,and the unit responsivity is 0.4 A/W.The maximum3 dB bandwidth of 24 GHz and a GB product of 360 GHz are achieved for the fabricated APD operating at 1.55μm.

Investigation of Ga_(2)O_(3)/diamond heterostructure solar-blind avalanche photodiode via TCAD simulation

A Ga_(2)O_(3)/diamond separate absorption and multiplication avalanche photodiode(SAM-APD)with mesa structure has been proposed and simulated.The simulation is based on an optimized Ga_(2)O_(3)/diamond heterostructure TCAD physical model,which is revised by repeated comparison with the experimental data from the literature.Since both Ga_(2)O_(3)and diamond are ultra-wide bandgap semiconductor materials,the Ga_(2)O_(3)/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 5×10^(4)and the peak responsivity can reach a value as high as 78 A/W.

Recent progress of SiC UV single photon counting avalanche photodiodes

4H-SiC single photon counting avalanche photodiodes(SPADs)are prior devices for weak ultraviolet(UV)signal detection with the advantages of small size,low leakage current,high avalanche multiplication gain,and high quantum efficiency,which benefit from the large bandgap energy,high carrier drift velocity and excellent physical stability of 4 H-SiC semiconductor material.UV detectors are widely used in many key applications,such as missile plume detection,corona discharge,UV astronomy,and biological and chemical agent detection.In this paper,we will describe basic concepts and review recent results on device design,process development,and basic characterizations of 4 H-SiC avalanche photodiodes.Several promising device structures and uniformity of avalanche multiplication are discussed,which are important for achieving high performance of 4 HSiC UV SPADs.

Avalanche photodiodes on silicon photonics

Silicon photonics technology has drawn significant interest due to its potential for compact and high-performance photonic integrated circuits.The Ge-or III-V material-based avalanche photodiodes integrated on silicon photonics provide ideal high sensitivity optical receivers for telecommunication wavelengths.Herein,the last advances of monolithic and hetero-geneous avalanche photodiodes on silicon are reviewed,including different device structures and semiconductor systems.

Short-wavelength infrared InAs/GaSb superlattice hole avalanche photodiode

We demonstrate two short-wavelength infrared avalanche photodiodes based on InAs/GaSb superlattice grown by metal-organic chemical vapor deposition.The difference between the two devices,namely,p+n-n+and p+nn-n+,is that the p+nn-n+device possesses an additional middle-doped layer to separate the multiplication region from the absorption region.By properly controlling the electric field distribution in the p+nn-n+device,an electric field of 906 kV/cm has been achieved,which is 2.6 times higher than that in the p+n-n+device.At a reverse bias of-0.1 V at 77 K,both devices show a 100%cut-off wavelength of 2.25μm.The p+n-n+and p+nn-n+show a dark current density of 1.5×10^-7 A/cm^2 and 1.8×10^-8 A/cm^2,and a peak responsivity about 0.35 A/W and 0.40 A/W at 1.5μm,respectively.A maximum multiplication gain of 55 is achieved in the p+nn-n+device while the value is only less than 2 in the p+n-n+device.Exponential nature of the gain characteristic as a function of reverse bias confirms a single carrier hole dominated impact ionization.

Bias-dependent timing jitter of 1-GHz sinusoidally gated InGaAs/InP avalanche photodiode

We characterized the dependence of the timing jitter of an InGaAs/InP single-photon avalanche diode on the excess bias voltage(V_(ex)) when operated in 1-GHz sinusoidally gated mode.The single-photon avalanche diode was cooled to-30 degrees Celsius.When the V_(ex) is too low(0.2 V-0.8 V) or too high(3 V-4.2 V),the timing jitter is increased with the V_(ex),particularly at high V_(ex).While at middle V_(ex)(1 V-2.8 V),the timing jitter is reduced.Measurements of the timing jitter of the same avalanche diode with pulsed gating show that this effect is likely related to the increase of both the amplitude of the V_(ex) and the width of the gate-on time.For the 1-GHz sinusoidally gated detector,the best jitter of 93 ps is achieved with a photon detection efficiency of 21.4%and a dark count rate of ~2.08×10^(-5) per gate at the V_(ex) of 2.8 V.To evaluate the whole performance of the detector,we calculated the noise equivalent power(NEP) and the afterpulse probability(P_(ap)).It is found that both NEP and P_(ap) increase quickly when the V_(ex) is above 2.8 V.At ~2.8-V V_(ex),the NEP and P_(ap) are ~2.06×10^(16)W/Hz^(1/2) and 7.11%,respectively.Therefore,the detector should be operated with V_(ex) of 2.8 V to exploit the fast time response,low NEP and low P_(ap).

Theoretical analysis for AlGaN avalanche photodiodes with mesa and field plate structure

To suppress the electric field crowding at sidewall and improve the detection sensitivity of the AlGaN separate absorption and multiplication(SAM)avalanche photodiodes(APDs),we propose the new AlGaN APDs structure combining a large-area mesa with a field plate(FP).The simulated results show that the proposed AlGaN APDs exhibit a significant increase in avalanche gain,about two orders of magnitude,compared to their counterparts without FP structure,which is attributed to the suppression of electric field crowding at sidewall of multiplication layer and the reduction of the maximum electric field at the p-type GaN sidewall in p-n depletion region.Meanwhile,the APDs can produce an obviously enhanced photocurrent due to the increase in cross sectional area of multiplication region.

Zener Phenomena in InGaAs/InAlAs/InP Avalanche Photodiodes

Avalanche photodiodes are widely utilized in research, military and commercial applications which make them attractive for further development. In this paper the results of numerical simulations of uncooled InGaAs/InAlAs/InP based photodiodes are presented. The devices were optimized for 1.55 μm wavelength detection. For device modeling the APSYS Crosslight software was used. Simulated structure consists of separate absorption, charge and multiplication layers with undepleted absorption region and thin charge layer. Based on numerical calculations, the device characteristics like band diagram, dark current, photo current, gain, breakdown voltage and gain bandwidth product were evaluated. The simulation results highlight importance of Zener effect in avalanche photodiode operation.

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.

InGaAs/InAlAs SAGCMCT avalanche photodiode with high linearity and wide dynamic range

Linearity is a very important parameter to measure the performance of avalanche photodiodes(APDs) under high input optical power. In this paper, the influence of the absorption layer on the linearity of APDs is carefully studied by using bandgap engineering with the structure model of separated absorption, grading, charge, multiplication, charge, and transit(SAGCMCT). The simulated results show that in the hybrid absorption layer device structure the 1 d B compression point can be improved from-9 d Bm to-2.1 d Bm by increasing the proportion of the p-type absorption layer. In the device structure with only one absorption layer, increasing the doping level of the absorption layer can also improve the 1 d B compression point from-8.6 d Bm to 1.43 d Bm at a gain of 10. Therefore, the absorption layer is very critical for the linearity of APDs.

Avalanche mechanism analysis of 4H-SiC n-i-p and p-i-n avalanche photodiodes working in Geiger mode

Understanding detailed avalanche mechanisms is critical for design optimization of avalanche photodiodes(APDs).In this work,avalanche characteristics and single photon counting performance of 4H-SiC n-i-p and p-i-n APDs are compared.By studying the evolution of breakdown voltage as a function of incident light wavelength,it is confirmed that at the deep ultraviolet(UV)wavelength region the avalanche events in 4H-SiC n-i-p APDs are mainly induced by hole-initiated ionization,while electron-initiated ionization is the main cause of avalanche breakdown in 4H-SiC p-i-n APDs.Meanwhile,at the same dark count rate,the single photon counting efficiency of n-i-p APDs is considerably higher than that of p-i-n APDs.The higher performance of n-i-p APDs can be explained by the larger impact ionization coefficient of holes in 4H-SiC.In addition,this is the first time,to the best of our knowledge,to report single photon detection performance of vertical 4H-SiC n-i-p-n APDs.

Background-Free Optical Sampling System Using Si Avalanche Photodiode as Two-Photon Absorber

The introduction of a double-chopping scheme eliminates the background level in the optical sampling system, where a Si avalanche photodiode acts as a two-photon absorber. We successfully demonstrate background-free optical sampling of 40-GHz and 160-GHz pulse trains.

Germanium-on-silicon avalanche photodiode for 1550 nm weak light signal detection at room temperature

To optimize the dark current characteristic and detection efficiency of the 1550 nm weak light signal at room temperature,this work proposes a Ge-on-Si avalanche photodiode[APD]in Geiger mode,which could operate at 300 K.This lateral separate absorption charge multiplication APD shows a low breakdown voltage[V_(br)]in Geiger mode of-7.42 V and low dark current of 0.096 n A at unity gain voltage[V_(Gain)=1=-7.03 V].Combined with an RF amplifier module and counter,the detection system demonstrates a low dark count rate[DCR]of 1.1×10^(6) counts per second and high detection efficiencyηof 7.8%for 1550 nm weak coherent pulse detection at 300 K.The APD reported in this work weakens the dependence of the weak optical signal recognition on the low environment temperature and makes single-chip integration of the single-photon level detection system possible.

Ultra-low detection delay drift caused by the temperature variation in a Si-avalanche-photodiode-based single-photon detector

We report a method to reduce the detection delay temperature drift for a single-photon detector based on the avalanche photodiode(SPAD). Both the SPAD and the comparator were temperature stabilized, resulting in an ultra-low temperature drift at 0.01 ps/°C. A stable time deviation as 0.15 ps over 1000 s was realized, while the ambient temperature fluctuated rapidly from 24°C to 44°C. To the best of our knowledge, this is the first report on the ultra-stable delay SPAD detector in the case of rapid increase or decrease of ambient temperature. It is helpful to improve the stability of onboard detectors for optical laser time transfer between ground and space.

Spatially modulated scene illumination for intensity-compensated two-dimensional array photon-counting LiDAR imaging

Photon-counting LiDAR using a two-dimensional(2D)array detector has the advantages of high lateral resolution and fast acquisition speed.The non-uniform intensity profile of the illumination beam and non-uniform quantum efficiency of the detectors in the 2D array deteriorate the imaging quality.Herein,we propose a photon-counting LiDAR system that uses a spatial light modulator to control the spatial intensity to compensate for both the non-uniform intensity profile of the illumination beam,and the variation in the quantum efficiency of the detectors in the 2D array.By using a 635 nm peak wavelength and 4 mW average power semiconductor laser,lab-based experiments at a 4.27 m stand-off distance are performed to verify the effectiveness of the proposed method.Compared with the unmodulated method,the standard deviation of the intensity image of the proposed method is reduced from 0.109 to 0.089 for a whiteboard target,with an average signal photon number of 0.006 per pixel.

Photoluminescence in wide band gap corundum Mg4Ta2O9 single crystals

As is well known,the basic intrinsic properties of materials can be significant for their practical applications.In this work,the room-temperature absorption,transmittance,reflectance spectra,and relative photoelectricities parameters of the Mg4Ta2O9 crystals are demonstrated.Meanwhile,the polarized Raman spectra of Mg4Ta2O9 crystals are also described.The room-temperature photoluminescence(PL)and the temperature-dependent PL for Mg4Ta2O9 crystals are obtained.Significantly,we observe a phonon-participated PL process in Mg4Ta2O9.

Adaptive Performance Improvement of Fiber Bragg Grating in Radio over Fiber System

The combination of Radio Frequency and Optical Fiber has resulted high capacity transmission at lower costs components and makes Radio over Fiber as a current trend of large broadband communication. In Fiber optics field, the use of Fiber Bragg Grating (FBG) was been proposed in recent research with different purpose of uses. However, the compensation of dispersion method of Fiber Bragg Grating (FBG) can boost significantly the system performance. This paper investigates the performance capacity improvement of adaptive Radio over Fiber system. The system design was performed using OptiSystem 7.0 software, which 10 Gb/s Non Return to Zero (NRZ) signal was launched into 50 Km Universal Mode Fiber and Fiber Bragg Grating was used as a compensator of dispersion before frequency up conversion. Therefore, the system performances were investigated by comparing the Bit Error Rate (BER) and Q-factors of Positive Intrinsic Negative (PIN) and Ultrafast Avalanche Photodiode (APD) as optical receivers. The Eye diagram analyzer showed acceptable improvement due to use of Fiber Bragg Grating as a compensator of dispersion.

Advances in near-infrared avalanche diode single-photon detectors

Avalanche-photodiode-based near-infrared single-photon detectors have seen rapid development in the last two decades because of their enormous internal gain,high sensitivity,fast response,small vol-ume,and ease of integration.The InGaAs/InP near-infrared single-photon detector is the most widely used avalanche diode at present.Its device performance is still being continuously improved through the optimization of device structure and external quenching circuits.This paper analyzes the latest development and application of these InGaAs/InP photodiodes,then briefly re views other near-infrared single-photon detection technologies based on new materials and new mechanisms.

Avalanche photodetectors based on two-dimensional layered materials

The past decade has witnessed a dramatic increase in interest in emerging photodetectors built from two-dimensional(2D)layered materials.A major driver of this trend is the growing demands for lightweight,uncooled,and even flexible photodetection technology.However,2D layered materials always suffer from low light absorption coefficients due to their atomically thin nature.Impact ionization,which can achieve carrier multiplication,is a promising strategy to design 2D photodetectors with high detection efficiency.In this review,typical types of photodetection mechanisms in 2D photodetectors are first summarized.We then discuss the avalanche mechanism induced by impact ionization and avalanche photodetectors based on conventional silicon and III–V compound semiconductors.Finally,a host of emerging avalanche photodetectors based on 2D materials and their van der Waals heterostructures,and their potential applications in the field of photon-counting technologies are detailed.By reviewing the recent progress and discussing challenges faced by 2D avalanche photodetectors,this review aims to provide perspectives on future research directions of 2D material-based ultrasensitive photodetectors such as single-photon detectors.