Avalanche Photodiode Device Research Articles

Integrated Encapsulation and Implementation of a Linear-Mode APD Detector for Single-Pixel Imaging Lidar

Single-pixel imaging lidar is a novel technology that leverages single-pixel detectors without spatial resolution and spatial light modulators to capture images by reconstruction. This technique has potential imaging capability in non-visible wavelengths compared with surface array detectors. An avalanche photodiode (APD) is a device in which the internal photoelectric effect and the avalanche multiplication effect are exploited to detect and amplify optical signals. An encapsulated APD detector, with an APD device as the core, is the preferred photodetector for lidar due to its high quantum efficiency in the near-infrared waveband. However, research into APD detectors in China is still in the exploratory period, when most of the work focuses on theoretical analysis and experimental verification. This is a far cry from foreign research levels in key technologies, and the required near-infrared APD detectors with high sensitivity and low noise have to be imported at a high price. In this present study, an encapsulated APD detector was designed in a linear mode by integrating a bare APD tube, a bias power circuit, a temperature control circuit and a signal processing circuit, and the corresponding theoretical analysis, circuit design, circuit simulation and experimental tests were carried out. Then, the APD detector was applied in the single-pixel imaging lidar system. The study showed that the bias power circuit could provide the APD with an operating voltage of DC 1.6 V to 300 V and a ripple voltage of less than 4.2 mV. Not only that, the temperature control circuit quickly changed the operating state of the Thermo Electric Cooler (TEC) to stabilize the ambient temperature of the APD and maintain it at 25 ± 0.3 °C within 5 h. The signal processing circuit was designed with a multi-stage amplification cascade structure, effectively raising the gain of signal amplification. By comparison, the trial also suggested that the encapsulated APD detector and the commercial Licel detector had a good agreement on the scattered signal, such as a repetition rate and pulse width response under the same lidar environment. Therefore, target objects in real atmospheric environments could be imaged by applying the encapsulated APD detector to the near-infrared single-pixel imaging lidar system.

GaAs/GaAsSb Core–Shell Configured Nanowire-Based Avalanche Photodiodes up to 1.3 μm Light Detection

We report the first study on a GaAs/GaAsSb core–shell (CS)-configured nanowire (NW)-based separate absorption, charge control, and multiplication region avalanche photodiode (APD) operating in the near-infrared (NIR) region. Heterostructure NWs consisted of GaAs and tunable band gap GaAs1–xSbx serving as the multiplication and absorption layers, respectively. A doping compensation of absorber material to boost material absorption, segment-wise annealing to suppress trap-assisted tunneling, and an intrinsic i-type and n-type combination of the hybrid axial core to suppress axial electric field are successfully adopted in this work to realize a room-temperature (RT) avalanche photodetection extending up to 1.3 μm. In an APD device operating at RT with a unity-gain responsivity of 0.2–0.25 A/W at ∼5 V, the peak gain of 160 @ 1064 nm and 18 V reverse bias, gain >50 @ 1.3 μm, are demonstrated. Thus, this work provides a foundation and prospects for exploiting greater freedom in NW photodiode design using hybrid axial and CS heterostructures.

High-Performance Lateral Avalanche Photodiode Based on Silicon-on-Insulator Structure

In this work, a silicon-on-insulator (SOI)-based lateral avalanche photodiode (APD) is proposed and fabricated. The device features lateral separate-absorption-multiplication (SAM) and electron-only injection. The bandwidth is optimized with the effective blocking of the deep photogenerated carriers by SOI structure. The device stability is also improved by additional shallow P-well region near the N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -region which can eliminate the edge breakdown induced by the curvature effect. Simulation results demonstrate that avalanche region (high electric field zone) is confined at the lateral PN <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> junction. Experimental fabrication and characterizations are further realized, and this SOI-based lateral APD device exhibits high responsivity (1.92 A/W at 7.8 V for 300 nm), low dark current (below 5 V), large bandwidth (12.4 GHz at 8.2 V), and low breakdown voltage (~7.8 V). The demonstrated device performance as well as the simple structure and good process compatibility can be attractive in future photo-detecting and advanced sensing applications.

Breakdown characteristics of deep-ultraviolet Al0.6Ga0.4N p-i-n avalanche photodiodes

A top-illuminated deep-ultraviolet Al0.6Ga0.4N p-i-n avalanche photodiode (APD) structure was designed and grown by metalorganic chemical vapor deposition on an AlN bulk substrate and on two different quality AlN/sapphire templates, and APDs were fabricated and tested. The APD devices with a circular diameter of 20 μm have demonstrated a distinctive reverse-bias breakdown behavior. The reverse breakdown voltage of the APDs is approximately −140 V, which corresponds to a breakdown electric field of 6–6.2 MV/cm for the Al0.6Ga0.4N material as estimated by Silvaco TCAD simulation. The APDs grown on the AlN bulk substrate show the lowest leakage current density of &amp;lt;1 × 10−8 A/cm2 (at low reverse bias) compared to that of the devices grown on the AlN templates. From the photocurrent measurement, a maximum gain (current limited) of 1.2 × 104 is calculated. The average temperature coefficients of the breakdown voltage are negative for APD devices fabricated from both the AlN bulk substrate and the AlN templates, but these data show that the coefficient is the least negative for the APD devices grown on the low-dislocation-density AlN bulk substrate.

A speed-optimized, low-noise APD with 0.18 μm CMOS technology for the VLC applications

A new avalanche photodiode device applied to a visible light communication (VLC) system is designed using a standard 0.18 [Formula: see text]m complementary metal oxide semiconductor process. Compared to regular CMOS APD devices, the proposed device adds a [Formula: see text]-well layer above the deep [Formula: see text]-well/[Formula: see text]-substrate structure, and an [Formula: see text]/[Formula: see text] layer is deposited upon it. The [Formula: see text]/[Formula: see text] layer acts as an avalanche breakdown layer of the device, and an STI structure is used to prevent the edge break prematurely. The simulation results shows that the avalanche breakdown voltage is as low as 9.9 V, dark current is below [Formula: see text] A under −9.5 V bias voltage, and the 3 dB bandwidth is of 5.9 GHz. It is due to the use of the 0.18 [Formula: see text]m CMOS process-specific STI protection ring and short-circuits the connection of the deep [Formula: see text]-well/[Formula: see text]-substrate, and the dark current is reduced to be lower than two orders of magnitude compared to regular CMOS APD. Gain and noise characteristics are accurately calculated from Hayat dead-space model applied to this CMOS APD. So, this device’s gain and excess noise factor are 20 and 2.5, respectively.

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.

Design and evaluation of a high-sensitivity digital receiver with the finite impulse response filter algorithm for free-space laser communication

We discuss the design of a digital laser communication receiver and its sensitivity test process. Laser communication is especially suitable for long-distance low-power micro–nano satellite links due to its narrow beam width, but the electro-optical noise situation of the micro–nano satellite platform is complicated and bad. Hence, it is necessary to introduce a digital laser communication receiver to flexibly suppress interference and noise to improve communication sensitivity. A digital laser communication receiver based on the avalanche photodiode (APD) is designed. Based on the principle of digital communication error probability, a high-sensitivity APD device is selected, and a digital receiving channel based on field programmable gate array is designed. The finite impulse response, the dynamic threshold, the baseband median, and other filtering algorithms are used to optimize the signal-to-noise ratio and enhance the detection sensitivity. At the same time, an 800-nm laser communication receiver sensitivity test experimental architecture is designed and the detection sensitivity experiment is carried out. The experiment indicates that the APD receiver achieves detection sensitivity at an Mbps rate better than −60 dBm. The digital filtering algorithm provides a filtering signal-to-noise ratio improvement of about 15 dB, which supplies a reference for the receiver design of micro–nano satellite laser communication.

Top-Illuminated In0.52Al0.48As-Based Avalanche Photodiode With Dual Charge Layers for High-Speed and Low Dark Current Performances

A novel type of top-illuminated, etch-mesa In0.52Al0.48As-based avalanche photodiode (APD) with high-speed (>25 Gb/s), low dark current performance has been demonstrated. The 25G APD device is composed of n-side down design with the In0.52Al0.48As multiplication (M) layer buried at the bottom to avoid the issues of surface breakdown and complex guard ring structure. In addition, we demonstrate that the new structure with two charge layers and triple mesas can effectively confine the electric-field within the center of M-layer and minimize the edge breakdown around the periphery of mesa. In contrast to the costly flip-chip bonding package with backside illumination, our demonstrated device is based on a simple top-illuminated structure that includes a large active diameter of 30 μm for easy optical alignment, a reasonable punch-through responsivity (0.7 A/W at 1.31 μm wavelength), and a good 3-dB optical-to-electrical (O-E) bandwidth (22.5 GHz) under low gain operations (MG = ∼3). Furthermore, it can sustain the 3-dB bandwidth of 15 GHz over a wide range of launched optical power (−17 to +4.6 dBm) under a moderate gain (MG = ∼5) operation at 1.31 μm wavelength. High-sensitivity (−16 dBm) for error-free 28 Gb/s operation can also be achieved at 1.55 μm wavelength.

4H–SiC Avalanche Photodiode Linear Array Operating in Geiger Mode

In this study, a 50-pixel linear array of 4H–SiC ultraviolet avalanche photodiodes operating in Geiger mode is reported for the first time. The 50 pixels within the linear array are all capable of detecting single photons but with a small number of them suffering from extra leakage current near avalanche breakdown. The enhanced leakage is likely correlated with structural defects existing within the epitaxial structure, which would lead to higher dark count rate (DCR) at the same single photon detection efficiency (SPDE) in Geiger mode. For a low-leakage avalanche photodiode device within the linear array, a room temperature SPDE of 15.4% at 280 nm is obtained with a corresponding DCR of 2.5 Hz/μm2.

Single-step metal-organic vapor-phase diffusion for low-dark-current planar-type avalanche photodiodes

In this paper, a p-type diffusion process based literally on single-step metal-organic vapor-phase diffusion (MOVPD) employing diethyl zinc as the diffusion source in combination with the recessetching technique is developed to improve the dark-current characteristics of planar-type avalanche photodiodes (APDs). The developed single-step MOVPD process exhibits on excellent linear relationship between the diffusion depth and the square root of the diffusion time, which mainly results from maintaining constant source diffusion. The single-step MOVPD process without any additional thermal activation process achieves a surface doping concentration of 1.9 × 1018 cm -3, which is sufficient to form ohmic contact. The measured diffusion profiles of the APDs clearly reveal the presence of a two-dimensional diffusion front formed by the recess-etched and guard-ring regions. The impact of this p-type diffusion process on the performance of the APD devices has also been demonstrated by exhibiting improved dark-current characteristics for the fabricated APDs.

Development of ZnSe‐based organic–inorganic hybrid UV‐APDs array

AbstractRecently, we have developed organic (PEDOT:PSS)–inorganic (ZnSSe) hybrid avalanche photodiode (APD) with long life time and its array. In this article, we review the development of the organic–inorganic hybrid‐type ZnSe‐based UV‐APDs array. We used PEDOT:PSS as UV transparent hole‐transport conducting polymer window layers formed by inkjet printing technique. We have successfully fabricated low dark current ultraviolet hybrid APDs. The hybrid APD device has exhibited very low voltage APD operation at 29 V and extremely low dark current of 10‐11 A/mm2 in the avalanche breakdownregion. The hybrid APD also has shown maximum multiplication factor of 45 and high sensitivity ∼ 3 A/W at the ultraviolet region (∼ 300 nm). A stable device operation is established using polyimide passivation and sealed package with N2 atmosphere. We also demonstrated integrated devices operation in APD mode with very small photosignal cross‐talk of ‐50 dB. The tail of current‐profile was determined as 8 μm by using in‐plane electron‐beam induced current (EBIC) measurement. (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Low dark current and stable ultraviolet avalanche photodiode of organic (PEDOT:PSS)‐inorganic (ZnSSe) hybrid junction structure

AbstractWe have developed organic‐inorganic hybrid avalanche photodiode (APD) with conducting polymer as a window layer on ZnSSe/n‐GaAs wafers. APD wafers used in this study were grown by molecular beam epitaxy (MBE). We used PEDOT:PSS as hole‐transport conducting polymer window layers formed by inkjet method. We have succeeded in fabrication of low dark current and stable ultraviolet hybrid APDs. The present device has exhibited very low voltage APD operation at 29 V and extremely low dark current of 10–11 A/mm2 in the avalanche breakdown region. The APD device also has shown maximum multiplication factor of 45 and high sensitivity ∼ 3 A/W at the ultraviolet region (∼ 300 nm). A stable device operation is established using polyimide passivation and sealed into package with N2 atmosphere. We also demonstrated integrated devices operation in PIN mode. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

High-Gain AlGaN Solar-Blind Avalanche Photodiodes

This letter reports high performance AlGaN solar-blind avalanche photodiodes (APDs) with separate absorption and multiplication structure grown by metal-organic chemical vapor deposition on AlN templates. In fabricating APD devices, we applied a photo-electrochemical treatment process after mesa etching to reduce damage induced by etching. After introducing this process, the leakage current of the fabricated devices was reduced obviously and a record-high gain of 1.2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> at the reverse bias of 84 V was achieved under the measurement condition with the protection current constrained to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> A.

Electrical modeling of InSb PiN photodiode for avalanche operation

Current density-voltage (J-V) characteristics at 77 K of InSb pin photodiodes, in dark condition and under illumination, were simulated in view to design an avalanche photodiode (APD). Theoretical J-V results were compared with experimental results, performed on InSb diode fabricated by molecular beam epitaxy, in order to validate the parameter values used for the modeling. Then, with the assumption of multiplication induced by the electrons, an optimized separate absorption and multiplication APD structure was defined by theoretically studying the absorber doping level and the multiplication layer thickness. Calculated gain value higher than 10 was achieved at V = −4.5 V. This result shows the potentiality of InSb material as APD device.

Proton radiation damage effects on the response of high speed communication avalanche photodiodes (notice of removal)

Subsequent to its publication in Optical Engineering, SPIE learned that a significant portion of this paper was previously published as “Harmful Proton Radiation Damage and Induced Bit Error Effects on the Performance of Avalanche Photodiode Devices,” in International Journal of Multidisciplinary Sciences and Engineering, Vol. 2, No. 4 (July 2011). Double publication violates SPIE Code of Ethics and consequently the paper has been removed from Optical Engineering by the publisher. The Authors

Design of a high sensitivity emitter-detector avalanche photodiode imager using very high transmittance, back-illuminated, silicon-on-sapphire

We present a detailed design study for a novel solid-state focal plane array of silicon avalanche photodiodes (APDs) using an advanced silicon-on-sapphire substrate incorporating an antireflective bilayer consisting of crystalline aluminum nitride (AlN) and amorphous, non-stoichiometric, silicon rich, silicon nitride (a-SiNX<1.33) between the silicon and sapphire. The substrate supports electrical and optical integration of a nearly 100% quantum efficiency, silicon APD capable of operating with wide dynamic range in dual linear or Geiger-mode, with a gallium nitride (GaN) laser diode in each pixel. The APD device and epitaxially grown GaN laser are fabricated within a crystallographically etched silicon mesa. The high resolution 27 μm emitter-detector pixel design enables single photon sensitive, solid-state focal plane arrays (FPAs), with passive and active imaging capability in a single FPA. The square 27 μm emitter-detector pixel achieves SNR>10 in active detection mode for Lambert surfaces at 20,000 m.

Investigation of a clinical PET detector module design that employs large-area avalanche photodetectors

We investigated the feasibility of designing an Anger-logic PET detector module using large-area high-gain avalanche photodiodes (APDs) for a brain-dedicated PET/MRI system. Using Monte Carlo simulations, we systematically optimized the detector design with regard to the scintillation crystal, optical diffuser, surface treatment, layout of large-area APDs, and signal-to-noise ratio (SNR, defined as the 511 keV photopeak position divided by the standard deviation of noise floor in an energy spectrum) of the APD devices. A detector prototype was built comprising an 8 × 8 array of 2.75 × 3.00 × 20.0 mm3 LYSO (lutetium-yttrium-oxyorthosilicate) crystals and a 22.0 × 24.0 × 9.0 mm3 optical diffuser. From the four designs of the optical diffuser tested, two designs employing a slotted diffuser are able to resolve all 64 crystals within the block with good uniformity and peak-to-valley ratio. Good agreement was found between the simulation and experimental results. For the detector employing a slotted optical diffuser, the energy resolution of the global energy spectrum after normalization is 13.4 ± 0.4%. The energy resolution of individual crystals varies between 11.3 ± 0.3% and 17.3 ± 0.4%. The time resolution varies between 4.85 ± 0.04 (center crystal), 5.17 ± 0.06 (edge crystal), and 5.18 ± 0.07 ns (corner crystal). The generalized framework proposed in this work helps to guide the design of detector modules for selected PET system configurations, including scaling the design down to a preclinical PET system, scaling up to a whole-body clinical scanner, as well as replacing APDs with other novel photodetectors that have higher gain or SNR such as silicon photomultipliers.

The development and performance of UV-enhanced APD-arrays for high resolution PET imaging coupled with pixelized Pr:LuAG crystal

The development of high-resolution, UV-enhanced avalanche photodiode (APD) arrays usable in high-resolution PET imaging is underway. These APD arrays were specifically designed as photosensors capable of direct coupling with pixelized Pr-doped Lu 3Al 5O 12 (Pr:LuAG) scintillators. An excellent quantum efficiency (QE) of 55% was achieved at the peak emission of Pr:LuAG (310 nm), namely, a substantial improvement from the QE ≤ 5 % as measured with the conventional Hamamatsu reverse-type APDs (S8664 series). Each APD device has 8×8 (TYP1) and 12×12 (TYP2) pixel structures with active areas of 3×3 mm 2 and 2×2 mm 2 in each pixel, respectively. A gain uniformity of ±8% and low dark noise of ≤ 2 nA / pixel have been achieved, measured at +25 °C. We also report on the large size single crystal growth of improved Pr:LuAG scintillators and the preliminary performance test of the same. An energy resolution of 4.2% (FWHM) was obtained for 662 keV gamma-rays for 10×10×10 mm 3 crystal, measured with a PMT employing a super-bialkali photocathode. We made a test module consisting of a UV-enhanced APD-array (either TYP1 or TYP2) optically coupled with an 8×8 (or 12×12) pixel Pr:LuAG matrix. The linearity between the output signals and incident gamma-ray energy of TYP1 and TYP2 gamma-ray detectors were only 0.27 and 0.33%, as measured at +25 °C for various gamma-ray sources, respectively. Energy resolutions of 7.0±0.2% (FWHM) and 9.0±0.6% (FWHM) were, respectively, obtained for TYP1 and TYP2 detector arrays for 662 keV gamma-rays. The uniformity of the pulse height distributions was also measured at less than 8% for both detectors. Finally, we measured the coincidence timing resolution of these gamma-ray detectors and obtained 4.0±0.1 ns (FWHM) for the 511 keV annihilation quanta from a 22Na source. These results suggest that UV-enhanced APD-arrays coupled with Pr:LuAG scintillators could be a promising device for future application in nuclear medicine.

Study of Wasted Space Effect in Avalanche Photodiodes: A New Look at the Size-Dependent Impact Ionization Properties under Submicron Scale

Impact ionization is one of the most important behaviors for carrier transport in high-field region. In this paper, we study the size-dependent impact ionization coefficients induced by the distance that the carriers have to travel to leave out of the terminal of the multiplication layer after the last impact ionization event, which is defined as the “wasted space”. Monte Carlo method is carried out to calculate the size-dependent impact ionization coefficients under submicron scale, and to investigate the effect of wasted space. The conventional model of mean multiplication gain in avalanche photodiodes (APDs) is revised with the adoption of size-dependent impact ionization coefficients, and a good agreement is achieved in the device characteristics of multiplication gain of InP-based APD devices.

Monte Carlo study of device characteristics of GaN-based avalanche photodiode devices

In this article, Monte Carlo method is used to study the characteristics of gallium nitride (GaN). Impact ionization is treated as an additional scattering mechanism, which is described by the Keldysh formula with the parameters determined by fitting the simulated results to the numerical calculation results. Based on simplified model, results of velocity overshoot and impact ionization rate of both carriers are calculated and analyzed. In addition, we get the device characteristics associated with impact ionization, i.e., gain, noise, and bandwidth (both electron- and hole-injected cases), which is compared to the reported experimental data and conventional theories. Moreover, we contrast the simulated device characteristics of GaN and the performance of several conventional materials.