Performance Of Avalanche Photodiodes Research Articles

Enhancing large-area Geiger-mode avalanche photodiode performance through dynamic memristor quenching: a study on improving count rate, reducing jitter and mitigating afterpulsing

While the larger photosensitive area of Geiger-mode avalanche photodiodes (GmAPDs) enhances their detection range and signal collection, improving their utility in weak light detection, their practicality is limited by a long recovery time, high afterpulsing probability (AP) and excessive jitter. Utilizing a dynamic memristor as a quenching resistor, this research improves the count rate of a large-size GmAPD by 100× at an overvoltage of 2.5 V, compared with a fixed resistor-quenched GmAPD. Furthermore, at a photon pulse frequency of 1 MHz jitter time is reduced from 3.60 ns to 0.48 ns, and the afterpulsing probability is effectively mitigated from 30.88% to 8.58%.

Window size dependence of gain and bandwidth in avalanche photodiodes with multiple multiplication layers under near Geiger-mode operation

We consider avalanche photodiodes (APDs) functioning under near Geiger-mode operation for extremely weak light (single or several photons) detection, such as in LiDAR receivers. To meet such demands, APDs which simultaneously have a large active window size, moderate bandwidth (∼GHz), and high internal gain (responsivity), are highly desired. However, it is difficult to design APDs capable of meeting the afore-mentioned performance requirements due to the intrinsic limitations of the gain-bandwidth product (GBP). In this work, we demonstrate that the GBP bottleneck in the APDs can be overcome by using multiple (3) In0.52Al0.48As based multiplication (M-) layers with a thick In0.53Ga0.47As absorber (2 µm). Moreover, the characteristic invariant 3-dB bandwidth in our APDs, from low to an extremely high operation gain, becomes more pronounced with an increase of its active window diameter (40 to 200 µm). This characteristic makes it very attractive for collecting weak light in free space as is required for LIDAR receiver applications. Comparison shows that the 200 µm APD exhibits a higher 0.9 Vbr responsivity (15 vs. 7 A/W), larger maximum gain (460 vs. 110), and higher GBP (468 vs. 131 GHz) than does the 40 µm reference sample and can sustain a constant 3-dB bandwidth (1.4 GHz) over a wide range of operation gains (10 to 460). The dependence of the APD performance on the window size can be attributed to the influence of the surface states on the edge of the etched mesa. Here, we further demonstrate a backside-illuminated structure with a flip-chip bonding package which minimizes this phenomenon in small APDs ensuring high-speed performance. Compared with the top-illuminated reference samples, the flip-chip bonding packaged device shows a further enhancement of the responsivity (10.7 vs. 7 A/W), 3-dB bandwidth (4.1 vs. 3.9 GHz), and saturation current (4.25 vs. 3.6 mA). The excellent static and dynamic performance of our flip-chip APD in turn leads to an unprecedented high velocity sensitivity (5 µm/sec) and superior quality 4-D FMCW LiDAR images compared to that obtainable with p-i-n-based or top-illuminated reference devices with the same small active window size (40 µm).

Photo-Electric response of 4H-SiC APDs at High-Level incident flux

In many applications, the highest and lowest detectable flux are both important for single photon avalanche photodiodes (APDs). The photocurrent and single-photon-counting performance of 4H-SiC APDs are investigated under a wide-range incident flux. Experimental results show that the photocurrent is sub-linearly with the incident photon rate at high-level incident flux. In addition, the ratio of photon count rate to dark count rate is non-monotonic when the incident flux increases. The highest detectable flux of the 4H-SiC APD can be extended from 3 × 103 photons/s·μm2 to more than 4 × 104 photons/s·μm2 by reducing the threshold voltage and increasing the reverse voltage.

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.

Study of HgCdTe (100) and HgCdTe (111)B Heterostructures Grown by MOCVD and Their Potential Application to APDs Operating in the IR Range up to 8 µm.

The trend related to reach the high operating temperature condition (HOT, temperature, T > 190 K) achieved by thermoelectric (TE) coolers has been observed in infrared (IR) technology recently. That is directly related to the attempts to reduce the IR detector size, weight, and power dissipation (SWaP) conditions. The room temperature avalanche photodiodes technology is well developed in short IR range (SWIR) while devices operating in mid-wavelength (MWIR) and long-wavelength (LWIR) require cooling to suppress dark current due to the low energy bandgap. The paper presents research on the potential application of the HgCdTe (100) oriented and HgCdTe (111)B heterostructures grown by metal-organic chemical vapor deposition (MOCVD) on GaAs substrates for the design of avalanche photodiodes (APDs) operating in the IR range up to 8 µm and under 2-stage TE cooling (T = 230 K). While HgCdTe band structure with molar composition xCd < 0.5 provides a very favorable hole-to-electron ionization coefficient ratio under avalanche conditions, resulting in increased gain without generating excess noise, the low level of background doping concentration and a low number of defects in the active layer is also required. HgCdTe (100) oriented layers exhibit better crystalline quality than HgCdTe (111)B grown on GaAs substrates, low dislocation density, and reduction of residual defects which contribute to a background doping within the range ~1014 cm–3. The fitting to the experimentally measured dark currents (at T = 230 K) of the N+-ν-p-P+ photodiodes commonly used as an APDs structure allowed to determine the material parameters. Experimentally extracted the mid-bandgap trap concentrations at the level of 2.5 × 1014 cm−3 and 1 × 1015 cm−3 for HgCdTe (100) and HgCdTe (111)B photodiode are reported respectively. HgCdTe (100) is better to provide high resistance, and consequently sufficient strength and uniform electric field distribution, as well as to avoid the tunneling current contribution at higher bias, which is a key issue in the proper operation of avalanche photodiodes. It was presented that HgCdTe (100) based N+-ν-p-P+ gain, M > 100 could be reached for reverse voltage > 5 V and excess noise factor F(M) assumes: 2.25 (active layer, xCd = 0.22, k = 0.04, M = 10) for λcut-off = 8 μm and T = 230 K. In addition the 4-TE cooled, 8 μm APDs performance was compared to the state-of-the-art for SWIR and MWIR APDs based mainly on III-V and HgCdTe materials (T = 77–300 K).

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 dB compression point can be improved from -9 dBm to -2.1 dBm 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 dB compression point from -8.6 dBm to 1.43 dBm at a gain of 10. Therefore, the absorption layer is very critical for the linearity of APDs.

Bit Error Performance of APD and SPAD Receivers in Optical Wireless Communication

This review concentrates on the state-of-the-art hardware-oriented receiver aspects for optical wireless communication (OWC), and points to the importance of BER performance analysis and modeling in presence of non-perpendicular light incidence. Receivers in OWC networks for 6G applications have to work for strongly different light incidence angles, to allow the formation of connections to locally separated transceivers without the need for rotation units and accurate adjustment. In turn, and in combination with fully integrated optical receivers, reduction of cost and increased comfort can be achieved. Fully integrated [bipolar] complementary metal-oxide-semiconductor ([Bi]CMOS) receivers with on-chip avalanche photodiodes (APDs) and single-photon avalanche diodes (SPADs) are presented and their performance in optical wireless communication is summarized. Impressive data rates up to 2 Gbit/s and free-space transmission distances up to 27 m at bit error ratios (BER) below 10−9 are reached with linear-mode APD receivers. The importance of optical interference in the isolation and passivation stack on top of the integrated photodiodes is illuminated. To be able to predict the dependence of the BER of single-photon avalanche diode (SPAD) receivers on the light incidence angle, a model, which includes a model for the photon detection probability and a standing-wave model for the isolation and passivation stack, is extended. The dependence of the BER on the light incidence angle onto the photodiodes is investigated by electromagnetic simulation for optical transmission of the layers on top of the photodiode, device simulation for the avalanche triggering probability and BER modeling with MATLAB. It is found that incidence angles up to 30° have moderate influence on the BER and that the BER degrades significantly for incidence angles larger than 50°.

Simulation of Extended Wavelength Avalanche Photodiode with the Type-II Superlattice Absorption Layer

The relationship between the performance of avalanche photodiode (APD) and structural parameters of the absorption, grading, and multiplication layers has been thoroughly simulated and discussed using the equivalent materials approach and Crosslight software. Based on separate absorption, grading, charge, and multiplication (SAGCM) structure, the absorption layer of APD was replaced with InGaAs/GaAsSb superlattice compared to conventional InGaAs/InP SAGCM APD. The results indicated that the breakdown voltage increased with the doping concentration of the absorption layer. When the thickness of the multiplication layer increased from 0.1 μm to 0.6 μm, the linear range of punchthrough voltage increased from 16 V to 48 V, and the breakdown voltage decreased at first and then increased when the multiplication layer reached the critical thickness at 0.35 μm. The grading layer could not only slow down the hole carrier, but also adjust the electric field. The dark current was reduced to about 10 nA and the gain was over 100 when the APD was cooled to 240 K. The response wavelength APD could be extended to 2.8 μm by fine tuning the superlattice parameters. The simulation results indicated that the APD using superlattice materials has potential to achieve a long wavelength response, a high gain, and a low dark current.

Evaluation and experimental comparisons of different photodetector receivers for visible light communication systems under typical scenarios

Positive-intrinsic-negative diode (PIN), avalanche photodiode (APD), and single photon avalanche diode (SPAD) are commonly used optoelectronic receivers with different characteristics in practical visible light communication system. To determine the most appropriate candidate, different signal and ambient light strength in the communication scenarios should be taken into account. APD and SPAD receivers have higher sensitivities than PIN, but there are still some defects that restrain their operation performance. APD receiver may generate excessive shot noise, whereas SPAD is limited by the dead time, afterpulsing, and smaller detection area. We initially analyze the noise characteristics of PIN, APD, and SPAD receivers. SNR models are established, and the main factors affecting the performance of APD and SPAD receivers are concluded. Then, the comparison experiments of three kinds of receivers in various transmission distances are conducted, respectively. Finally, the experimental results show that: short and mid distance conditions, PIN and APD are better choices, whereas SPAD performs better in long-distance communication. In addition, if a certain intensity of ambient light is introduced, APD is still better than SPAD even in long distance.

Avalanche photodetectors with photon trapping structures for biomedical imaging applications.

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 photon trapping nanostructures for photons with 450 nm and 850 nm wavelengths. At 850 nm wavelength, our photon trapping avalanche photodiodes showed 30 times higher gain, an increase from 16% to >60% enhanced absorption efficiency, and a 50% reduction in the full width at half maximum (FWHM) pulse response time close to the breakdown voltage. At 450 nm wavelength, the external quantum efficiency increased from 54% to 82%, while the gain was enhanced more than 20-fold. Therefore, silicon APDs with photon trapping structures exhibited a dramatic increase in absorption compared to control devices. Results suggest very thin devices with fast timing properties and high absorption between the near-ultraviolet and the near infrared region can be manufactured for high-speed applications in biomedical imaging. This study paves the way towards obtaining single photon detectors with photon trapping structures with gains above 106 for the entire visible range.

Mechanism of dark current dependence on reverse voltage in mid-wavelength infrared HgCdTe mesa PIN avalanche diode

Mid-wavelength infrared HgCdTe avalanche photodiodes (APDs) are becoming increasingly significant in research and practical applications for the high linear gain, low excess noise and high quantum efficiency. However, the performance of HgCdTe APDs is largely limited by the voltage dependence of dark current. It has been well known that the tunneling current is the main component of the dark current of the p-i-n diode. However, the current contribution of different physical mechanism still needs to be indicated in different reverse voltages. In this paper, we mainly study the mechanism of the relationship between dark current and reverse voltage of mid-wavelength infrared $${\text{Hg}}_{1 - x} {\text{Cd}}_{x} {\text{Te}}$$ (x = 0.3) mesa p-i-n avalanche diode. Several physical models are used for the dark current numerical simulation. The results show that for detection of $${\text{Hg}}_{1 - x} {\text{Cd}}_{x} {\text{Te}}$$ mesa p-i-n detector under low temperature, dark current is mainly caused by tunneling current. With the reverse voltage increasing, the main component of dark current turns from trap-assisted tunneling current to direct band-to-band tunneling. The transition voltage is positively related to the energy level difference between trap energy level and conduction band. The results may provide a guideline to improve the performance of the mid-wavelength infrared APD detector by ranking the importance of different structural parameters.

Impact of Resistance on the Performance of Ultraviolet 4H-SiC Avalanche Photodiodes

In this work, ultraviolet (UV) 4H-SiC avalanche photodiodes (APDs) with a diameter of $\mu \text{m}$ were fabricated and investigated. The impact of resistance on the performance of 4H-SiC APDs was analyzed both in linear and Geiger modes. The optical response time of the fabricated APD devices in linear mode was measured with various load resistances, whereas the single photon counting performance in Geiger mode was carried out based on the passive-quenching circuit with different quenching resistances. The results show that the response time and the single-photon counting performance are strongly dependent on the series resistances. The response time (i.e., rising time and falling time) in the linear mode increases almost linearly with the load resistance increasing. In the Geiger mode, the photon count rate (PCR) decreases with the increasing quenching resistance. However, at some reverse bias voltages, the ratio of single photon detection efficiency (SPDE) to dark count rate (DCR) is positively correlated to the quenching resistance. Therefore, in order to obtain the optimal performance of 4H-SiC APDs, the resistance in the circuit must be carefully adjusted for practical usage. The results in this work will be very useful and can provide a reference for researchers in the fields of 4H-SiC APD UV detectors.

Temperature effects on characteristics and performance of near-infrared wide bandwidth for different avalanche photodiodes structures

In this paper, the influences of thermal and spectral variations on various structures of avalanche photodiodes (APDs) have been deeply investigated. The characteristics and performance of Silicon (Si), Gallium Arsenide (GaAs) and Indium Gallium Arsenide (InGaAs) avalanche photodiodes have been evaluated under effects of different temperature degrees. The impacts of different temperature levels on the band gap energy, detector responsivity, noise equivalent power (NEP), cut-off wavelength, dark current and the photocurrent are studied and analyzed in details. The signal to noise ratio (SNR) and Bit Error Rate (BER) of these APDs are also computed and measured under the influences of different temperature levels and spectral variations. The aim of this paper is to determine the most efficient avalanche photodiode achieving the best performance according to the maximum SNR and minimum BER at high temperature environments. The analysis of the proposed model is performed by MATLAB. It was found that the experimental measured results endorse the analytical computed results. Further, it was observed that the APD (InGaAs) provides performance better than other APD structures in terms of larger SNR and less BER at higher temperature levels. Also, the temperature has a slight effect on the performance of APD (GaAs). So, it is seemed to be stable more than other APD structures and recommended to be used in warm environments and for high temperature applications.

Performance Modulation for Back-Illuminated AlGaN Ultraviolet Avalanche Photodiodes Based on Multiplication Scaling

Back-illuminated Al0.1Ga0.9N ultraviolet avalanche photodiodes (APDs) of various multiplication widths were fabricated on AlN templates with a separate absorption and multiplication structure. The impacts of an increased multiplication scale on a device performance were investigated. The avalanche breakdown voltage was found to increase as the multiplication layer thickness (MLT) increases. The APD with 230-nm-MLT achieved a superior maximum multiplication gain of 5.4 × 10 4 , higher than that obtained in devices with 150-nm- and 300-nm-MLT. Theoretical simulations demonstrated that the critical electric field intensity in an avalanche region would decrease as the rising of MLT, indicating the modulating ability of multiplication scaling on the AlGaN APD performance. In addition, APDs fabricated on different AlN templates were employed to study the effects of crystalline quality on device properties.

Analysis of Defect-Related Electrical Fatigue in 4H-SiC Avalanche Photodiodes

SiC-based avalanche photodiodes (APDs) are the preferred devices for use in high-sensitivity UV detectors. However, the defect densities on the surface or in the bulk of the SiC epitaxial layer limit the performance of APDs. In this study, the effect of defects resulting in electrical fatigue in 4H-SiC APDs on device performance was analyzed. Further, fast and efficient defect analysis and detection methods based on laser scanning confocal microscopy are proposed for high-performance APD fabrication. Experimental results show a correlation between the electrical transport and optical properties with respect to the defect behavior in the active and non-active area based on the physical morphology.

An excess noise measurement system for weak responsivity avalanche photodiodes

A system for measuring, with reduced photocurrent, the excess noise associated with the gain in avalanche photodiodes (APDs), using a transimpedance amplifier front-end and based on phase-sensitive detection is described. The system can reliably measure the excess noise power of devices, even when the un-multiplied photocurrent is low (~10 nA). This is more than one order of magnitude better than previously reported systems and represents a significantly better noise signal to noise ratio. This improvement in performance has been achieved by increasing the value of the feedback resistor and reducing the op-amp bandwidth. The ability to characterise APD performance with such low photocurrents enables the use of low power light sources such as light emitting diode rather than lasers to investigate the APD noise performance.

Noise Characterization of Geiger-Mode 4H-SiC Avalanche Photodiodes for Ultraviolet Single-Photon Detection

We present here the noise properties of the 4H-SiC avalanche photodiodes (APD) operated in Geiger mode. After-pulse events together with the dark count rate were measured at different temperatures. We found that at a certain bias voltage, the after-pulse probability of the 4H-SiC APD was dependent on the incident photon flux. This interesting observation may be useful to build a photon-number resolving detector for the UV regime. Moreover, the after-pulse and the dark counts noise decreased as the temperature dropped from room temperature to −;40 °C so that the single-photon detection performance of the 4H-SiC APD could be improved by decreasing the operation temperature.

Analysis of Dark Count Mechanisms of 4H-SiC Ultraviolet Avalanche Photodiodes Working in Geiger Mode

In this paper, the dark count mechanisms of 4H-SiC ultraviolet avalanche photodiodes (APDs) working in Geiger mode are studied by temperature-dependent characterizations. At temperatures above 260 K, the activation energy derived from the dark count characteristics is much less than half of the bandgap of 4H-SiC. Trap-assisted tunneling is determined as the dominant carrier transport mechanism in this temperature regime, which is supported by the observed capacitance frequency dispersion and low-temperature persistent photoconductivity effect. As temperature further decreases, the temperature dependence of dark count rate (DCR) becomes weaker, suggesting that band-to-band tunneling starts to play a role in the dark count generation process, which turns into the major mechanism below 120 K. As a consequence, one way to suppress dark counts for SiC APDs is to inhibit tunneling process, which can be realized by increasing the intrinsic layer thickness. In addition, it is found that when the single photon detection efficiency is in the range of 0%–30%, the DCR of the SiC APD can be reduced by an order of magnitude as temperature decreases from room temperature to 77 K, which is the first report of low-temperature performance of SiC APDs.

4H-SiC Ultraviolet Avalanche Photodiodes With Small Gain Slope and Enhanced Fill Factor

In this paper, 4H-SiC separated absorption charge and multiplication ultraviolet avalanche photodiodes (APDs) with small gain-voltage slope and enhanced fill factor are designed and fabricated. As a special reach-through structure, the absorption layer of the APD is fully depleted at breakdown voltage, which can share a considerable portion of reverse bias. As a result, the sensitivity of electric field within the multiplication layer as a function of overbias is reduced, leading to a small gain slope. Given the fact that the impact ionization coefficient of holes is less sensitive to electric field variation than that of electrons, the APD is also designed to be a hole-initiated ionization type, which can further reduce the gain slope. Meanwhile, three different top-electrode geometric patterns of SiC APDs are designed, and their impact on APD performance is investigated for the first time. Severe current crowding effect is observed in the forward current–voltage (I–V) characteristics of the APD with a traditional dot top-electrode, indicating inefficient current spreading across the top contact layer due to nonnegligible lateral resistance. In contrast, the forward I–V characteristics and photo-current at the avalanche regime of the APDs with optimized branch-shaped top-electrodes are apparently improved, owing to the improvement of electric field distribution and avalanche multiplication uniformity across the device active area. Furthermore, photon count rate increases by two to four times with larger voltage pulse height, suggesting enhanced effective avalanche multiplication area and fill factor.

Enhanced Carrier Multiplication in InAs Quantum Dots for Bulk Avalanche Photodetector Applications

Exploring the potentiality of enhancing the performance of avalanche photodiodes (APDs) using novel nanoscale structures is highly attractive for overcoming the bottleneck of avalanche probability. This work demonstrates, for the first time, multiplication enhancement of electron‐initiated photocurrent due to impact ionization in InAs quantum dots (QDs) within a GaAs APD structure. A five‐layer stacked 2.25 MLs InAs QD/50 nm GaAs spacer multiplication structure integrated into a separated absorption, charge, and multiplication GaAs homo APD results in up to six times higher multiplication factors in comparison to a reference device without QD over a temperature range of 77–300 K. In addition, extremely low excess noise factor in close proximity to that of silicon is also observed with an effective k eff factor below 0.1. This demonstration is of fundamental interest and relevant for future ultra efficient avalanche detector applications.