Separate Absorption , Charge And Multiplication Research Articles

Spatial Nonuniformity of Photoresponse in SiC UV Avalanche Photodiodes Operating in Linear and Geiger Mode

Silicon Carbide's intrinsic material properties, along with the availability of low-defect density, 6" substrates, make it an attractive material system for visible-blind ultraviolet (UV) detectors. Avalanche photodiodes (APDs) made from SiC have been shown to operate both as linear mode detectors with high gain (>10⁷) and as single-photon avalanche detectors (SPADs) with competitive photon detection efficiency. However, reported spatial non-uniformities in photoresponse of these devices will reduce sensitivity [1,2].In this paper, we examine the impact of device geometry, epitaxial variations, and crystal anisotropy on the spatial uniformity of photoresponse in SiC APDs. Photoresponse maps are generated using a fast 285 nm pulsed LED source that is tightly focused to a ~10 µm spot. Response maps are measured for devices with different geometries fabricated on the same chip in both linear-mode and Geiger-mode. Measurements on standard pin diodes will be presented, along with separate absorption, charge, and multiplication (SACM) structures.Experimental results indicate that all devices exhibit localized regions of high photoresponse at gain > 1000 and that the spreading of the photoresponse is highly directional. Finger diodes with 120 μm x 30 μm mesas exhibit good response uniformity with a variation < 30% across the device. In contrast, diodes with 60 and 90 μm square-shaped mesas exhibit similar uniform response spreading along one edge that is bounded by the size of the mesa, but a >10x drop in relative response over ~30-40 μm in the orthogonal direction which is much shorter than the extent of the mesa. Devices with 100 μm circular mesas exhibit somewhat similar results to the square diodes, but with the presence of multiple hot spots in response.Experimental results are analyzed through 3D numerical modeling of devices which accounts for the effects of doping and thickness variations across the substrate as well as the anisotropy of impact ionization. Modeling indicates that small variations in the thickness in the drift regions of a diode can yield meaningful variations in avalanche gain across the mesa. The impact of anisotropic impact ionization will be considered using full-band 3D Monte Carlo calculations. X. Bai, H.-D. Liu, D. C. McIntosh and J. C. Campbell, "High-Detectivity and High-Single-Photon-Detection-Efficiency 4H-SiC Avalanche Photodiodes," IEEE J. Quantum Electron. 45 300-303 (2009). DOI: 10.1109/JQE.2009.2013093.L. Su et al, "Recent progress of SiC UV single photon counting avalanche photodiodes," J. Semicond. 40 121802 (2019). DOI: 10.1088/1674-4926/40/12/121802. Figure 1

A peak enhancement of frequency response of waveguide integrated silicon-based germanium avalanche photodetector

Avalanche photodetectors (APDs) featuring an avalanche multiplication region are vital for reaching high sensitivity and responsivity in optical transceivers. Waveguide-coupled Ge-on-Si separate absorption, charge, and multiplication (SACM) APDs are popular due to their straightforward fabrication process, low optical propagation loss, and high detection sensitivity in optical communications. This paper introduces a lateral SACM Ge-on-Si APD on a silicon-on-insulator (SOI) wafer, featuring a 10 μm-long, 0.5 μm-wide Ge layer at 1310 nm on a standard 8-inch silicon photonics platform. The dark current measures approximately 38.6 μA at −21 V, indicating a breakdown voltage greater than −21 V for the device. The APDs exhibit a unit-gain responsivity of 0.5 A/W at −10 V. At −15 V, their responsivity reaches 2.98 and 2.91 A/W with input powers of −10 and −25 dBm, respectively. The device's 3-dB bandwidth is 15 GHz with an input power of −15 dBm and a gain is 11.68. Experimental results show a peak in impedance at high bias voltages, attributed to inductor and capacitor (LC) circuit resonance, enhancing frequency response. Furthermore, 20 Gbps eye diagrams at −21 V and −9 dBm input power reveal signal to noise ratio (SNRs) of 5.30. This lateral SACM APD, compatible with the stand complementary metal oxide semiconductor (CMOS) process, shows that utilizing the peaking effect at low optical power increases bandwidth.

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 guardring-free 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 0.9V br, and the unit responsivity is 0.4 A/W. The maximum 3 dB bandwidth of 24 GHz and a GB product of 360 GHz are achieved for the fabricated APD operating at 1.55 μm.

High electric field characteristics of GaAsSb photodiodes on InP substrates

Low noise avalanche photodiodes (APDs) detecting 1550 nm wavelength play a crucial role in optical communication and LiDAR systems. These APDs utilize a separate absorption, charge, and multiplication (SACM) architecture with an absorber for 1400–1650 nm detection and a low noise, high gain multiplier that can be independently optimized for a high signal-to-noise ratio. Recently, GaAs0.5Sb0.5/Al0.85Ga0.15As0.56Sb0.44 SACM APDs have demonstrated ultra-high gain and extremely low noise, possibly improving sensitivity over Si and InGaAs/InP commercial APDs. This accomplishment was achieved using a GaAsSb absorber instead of a conventional InGaAs absorber, mitigating band discontinuities between the absorber and the multiplier. However, further optimization is required to reduce noise due to tunneling and impact ionization from the GaAsSb absorber, which occurs at a high electric field region. This paper focuses on the study of the high-field characteristics of GaAsSb photodiodes (PDs). The tunneling phenomenon is analyzed through current density-voltage measurements, and the impact ionization behavior is evaluated by measuring the multiplication of p-i-n GaAsSb PDs. The result suggests that when designing a SACM APD with a GaAsSb absorber, the electric field in the absorber can be increased to 175 kV/cm without the detrimental effects of ionization occurring in the absorber. The findings from this investigation will assist in optimizing GaAsSb-based SACM APDs and promoting further advancements in the 1550 nm APD technology.

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 &lt; 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.

Linear Mode Avalanche Photodiodes With Antimonide Multipliers on InP Substrates

We provide an overview of our progress on the development of linear mode avalanche photodiodes (LmAPDs) on InP substrates using antimony (Sb)-based multipliers for short-wavelength infrared (SWIR) spectral region. We identify the key figures of merit of LmAPDs to provide higher sensitivity and speed for applications like light detection and ranging (LiDAR) and remote sensing. We discuss the design of separate absorption, charge, and multiplication (SACM) APDs that are used for narrow gap absorption. We summarize our results on the impact ionization, multiplication gain, dark current, and excess noise of AlGaAsSb and AlInAsSb multipliers lattice-matched to InP substrates. Finally, we identify the key technical challenges associated with the development of SACM APDs on InP substrates.

High-Performance Waveguide-Integrated Ge/Si Avalanche Photodetector with Lateral Multiplication Region

High-performance waveguide-integrated Ge/Si APDs in separate absorption, charge, and multiplication (SACM) schemes have been exploited to facilitate energy-efficient optical communication and interconnects. However, the charge layer design is complex and time-consuming. A waveguide-integrated Ge/Si avalanche photodetector (APD) is proposed in a separate absorption and multiplication (SAM) configuration. The device can work at low voltage and high speed with a lateral multiplication region without complexity of the charge layer. The proposed device is implemented by the complementary metal-oxide-semiconductor (CMOS) process in the 8-inch Si photonics platform. The device has a low breakdown voltage of 12 V and shows high responsivity of 15.1 A/W at 1550 nm wavelength under optical power of −22.49 dBm, corresponding to a multiplication gain of 18.1. Moreover, an opto-electrical bandwidth of 20.7 GHz is measured at 10.6 V. The high-speed performance at low voltage shows a great potential to implement high-energy-efficient Si optical communications and interconnections.

Ensemble GaAsSb/GaAs axial configured nanowire-based separate absorption, charge, and multiplication avalanche near-infrared photodetectors.

In this study, molecular beam epitaxially grown axially configured ensemble GaAsSb/GaAs separate absorption, charge, and multiplication (SACM) region-based nanowire avalanche photodetector device on non-patterned Si substrate is presented. Our device exhibits a low breakdown voltage (VBR) of ∼ −10 ± 2.5 V under dark, photocurrent gain (M) varying from 20 in linear mode to avalanche gain of 700 at VBR at a 1.064 μm wavelength. Positive temperature dependence of breakdown voltage ∼ 12.6 mV K−1 further affirms avalanche breakdown as the gain mechanism in our SACM NW APDs. Capacitance–voltage (C–V) and temperature-dependent noise characteristics also validated punch-through voltage ascertained from I–V measurements, and avalanche being the dominant gain mechanism in the APDs. The ensemble SACM NW APD device demonstrated a broad spectral room temperature response with a cut-off wavelength of ∼1.2 μm with a responsivity of ∼0.17–0.38 A W−1 at −3 V. This work offers a potential pathway toward realizing tunable nanowire-based avalanche photodetectors compatible with traditional Si technology.

AlxIn1-xAsySb1-y photodiodes with low avalanche breakdown temperature dependence.

We report AlxIn1-xAsySb1-y PIN and Separate Absorption, Charge and Multiplication (SACM) avalanche photodiodes (APDs) with high temperature stability. This work is based on measurements of avalanche breakdown voltage of these devices for temperatures between 223 K and 363 K. Breakdown voltage temperature coefficients are shown to be lower than those of APDs fabricated with other materials with comparable multiplication layer thicknesses.

Frequency response and modeling of resonant-cavity separate absorption, charge, and multiplication avalanche photodiodes

A theoretical model incorporating the mechanism of resonant absorption of the multiple reflected lightwaves is presented for the frequency response of resonant-cavity (RC) separate absorption, charge, and multiplication (SACM) avalanche photodiodes (APDs). The derived theoretical expressions are general and can be readily applied to many other RC and non-RC APDs. These analytical expressions also allow for fast computation of the frequency response and bandwidth characteristics. Combining this frequency response theory with expressions of multiplication gain and ionization coefficients, an efficient approach is proposed for modeling the general performance characteristics of RC APDs. The modeling approach is applied to an InGaAs-AlGaAs RC SACM APD. The computed results are demonstrated, and the results of -3 dB bandwidth are comparable to experimental work. The validity of the modeling parameters is also discussed. It is further found that the normalized frequency response is unaffected when the value of the absorption coefficient is changed, suggesting that the standing-wave effect within the RC structure may not influence the bandwidth characteristics.