Abstract
Al
0.85
Ga
0.15
As
0.56
Sb
0.44
has recently attracted significant research interest as a material for 1550 nm low-noise short-wave infrared (SWIR) avalanche photodiodes (APDs) due to the ...very wide ratio between its electron and hole ionization coefficients. This work reports new experimental excess noise data for thick Al
0.85
Ga
0.15
As
0.56
Sb
0.44
PIN and NIP structures, measuring low noise at significantly higher multiplication values than previously reported (
F
= 2.2 at
M
= 38). These results disagree with the classical McIntyre excess noise theory, which overestimates the expected noise based on the ionization coefficients reported for this alloy. Even the addition of ‘dead space’ effects cannot account for these discrepancies. The only way to explain the low excess noise observed is to conclude that the spatial probability distributions for impact ionization of electrons and holes in this material follows a Weibull–Fréchet distribution function even at relatively low electric-fields. Knowledge of the ionization coefficients alone is no longer sufficient to predict the excess noise properties of this material system and consequently the electric-field dependent electron and hole ionization probability distributions are extracted for this alloy.
High-sensitivity avalanche photodiodes (APDs) are used to amplify weak optical signals in a wide range of applications, including telecommunications, data centers, spectroscopy, imaging, light ...detection and ranging, medical diagnostics, and quantum applications. This paper reports antimony-based separate absorption, charge, and multiplication structure APDs on InP substrates. Al0.7In0.3As0.79Sb0.21 is used for the multiplier region, and InGaAs is used as the absorber. The excess noise is comparable to that of silicon APDs; the k-value is more than one order of magnitude lower than that of APDs that use InP or InAlAs for the gain region. The external quantum efficiency without an anti-reflection coating at 1550 nm is 57%. The gradient of the temperature coefficient of avalanche breakdown voltage is 6.7 mV/K/μm, which is less than one-sixth that of InP APDs, presenting the potential to reduce the cost and complexity of receiver circuits. Semi-insulating InP substrates make high-speed operation practical for widely reported AlxIn1−xAsySb1−y-based APDs.
We report high-gain, low-noise-figure, and high linearity analog photonic links at 1064 nm using InP/InGaAs modified uni-traveling-carrier (MUTC) photodiodes. Balanced photodiodes reach output powers ...of 17.7 dBm, 19.8 dBm, 20.7 dBm, and 22 dBm at 38 GHz, 29 GHz, 27 GHz, and 24.5 GHz, respectively. High common-mode rejection ratio (CMRR) of 25 dB and good linearity with a third-order intercept point (OIP3) of up to 34 dBm were measured at 38 GHz for 10-μm-diameter balanced photodiodes. We demonstrate two analog photonic links with different noise reduction techniques without electronic amplification. In the first link, we use balanced detection with a quadrature-biased Mach-Zehnder modulator (MZM) for noise cancellation. Link gain of 6.8 dB, noise figure (NF) of 25.8 dB and spurious free dynamic range (SFDR 3 ) of 114 dB·Hz 2/3 at 38 GHz were achieved. The second link works at low bias modulation for improved signal-to-noise ratio with a single photodetector. Record-high gain (19.3 dB at 26 GHz and 17 dB at 38 GHz) and low noise figure (14.5 dB at 26 GHz and 17 dB at 38 GHz) were demonstrated.
Abstract
The fast development of mid-wave infrared photonics has increased the demand for high-performance photodetectors that operate in this spectral range. However, the signal-to-noise ratio, ...regarded as a primary figure of merit for mid-wave infrared detection, is strongly limited by the high dark current in narrow-bandgap materials. Therefore, conventional mid-wave infrared photodetectors such as HgCdTe require cryogenic temperatures to avoid excessively high dark current. To address this challenge, we report an avalanche photodiode design using photon-trapping structures to enhance the quantum efficiency and minimize the absorber thickness to suppress the dark current. The device exhibits high quantum efficiency and dark current density that is nearly three orders of magnitude lower than that of the state-of-the-art HgCdTe avalanche photodiodes and nearly two orders lower than that of previously reported AlInAsSb avalanche photodiodes that operate at 2 µm. Additionally, the bandwidth of these avalanche photodiodes reaches ~7 GHz, and the gain–bandwidth product is over 200 GHz; both are more than four times those of previously reported 2 µm avalanche photodiodes.
The InGaAs lattice-matched to InP has been widely deployed as the absorption material in short-wavelength infrared photodetection applications such as imaging and optical communications. Here, a ...series of digital alloy (DA)-grown InAs/GaAs short-period superlattices were investigated to extend the absorption spectral range. The scanning transmission electron microscopy, high-resolution X-ray diffraction, and atomic force microscopy measurements exhibit good material quality, while the photoluminescence (PL) spectra demonstrate a wide band gap tunability for the InGaAs obtained via the DA growth technique. The photoluminescence peak can be effectively shifted from 1690 nm (0.734 eV) for conventional random alloy (RA) InGaAs to 1950 nm (0.636 eV) for 8 monolayer (ML) DA InGaAs at room temperature. The complete set of optical constants of DA InGaAs has been extracted via the ellipsometry technique, showing the absorption coefficients of 398, 831, and 1230 cm–1 at 2 μm for 6, 8, and 10 ML DA InGaAs, respectively. As the period thickness increases for DA InGaAs, a red shift at the absorption edge can be observed. Furthermore, the simulated band structures of DA InGaAs via an environment-dependent tight binding model agree well with the measured photoluminescence peaks, which is advantageous for a physical understanding of band structure engineering via the DA growth technique. These investigations and results pave the way for the future utilization of the DA-grown InAs/GaAs short-period superlattices as a promising absorption material choice to extend the photodetector response beyond the cutoff wavelength of random alloy InGaAs.
We report the frequency response of Al
0.3
InAsSb/Al
0.7
InAsSb nBn photodetectors. The 3-dB bandwidth of the devices varies from ∼ 150 MHz to ∼ 700 MHz with different device diameters and saturates ...with bias voltage immediately after the device turn on. A new equivalent circuit model is developed to explain the frequency behavior of nBn photodetectors. The simulated bandwidth based on the new equivalent circuit model agrees well with the bandwidth and the microwave scattering parameter measurements. The analysis reveals that the limiting factor of the bandwidth of the nBn photodetector is the large diffusion capacitance caused by the minority carrier lifetime and the device area. Additionally, the bandwidth of the nBn photodetector is barely affected by the photocurrent, which is found to be caused by the barrier structure in the nBn photodetector.
Lithium niobate on insulator (LNOI) has become an intriguing platform for integrated photonics for applications in communications, microwave photonics, and computing. Whereas, integrated devices ...including modulators, resonators, and lasers with high performance have been recently realized on the LNOI platform, high-speed photodetectors, an essential building block in photonic integrated circuits, have not been demonstrated on LNOI yet. Here, we demonstrate for the first time, heterogeneously integrated modified uni-traveling carrier photodiodes on LNOI with a record-high bandwidth of 80 GHz and a responsivity of 0.6 A/W at a 1550-nm wavelength. The photodiodes are based on an n-down InGaAs/InP epitaxial layer structure that was optimized for high carrier transit time-limited bandwidth. Photodiode integration was achieved using a scalable wafer die bonding approach that is fully compatible with the LNOI platform.
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.
Digital alloy and random alloy Al 0.85 Ga 0.15 As 0.56 Sb 0.44 avalanche photodiodes (APDs) exhibit low excess noise, comparable to Si APDs. Consequently, this material is a promising multiplication ...layer candidate for separate absorption, charge, and multiplication structure APDs with high gain-bandwidth product. Characterization of the impact ionization coefficients of electrons ( α ) and holes ( β ) plays an important role in the simulation of avalanche photodiodes. The multiplication gain curves of eight p + -i-n + and n + -i-p + APDs covering a wide range of avalanche widths have been used to determine the electric field dependence of the impact ionization coefficients of Al 0.85 Ga 0.15 As 0.56 Sb 0.44 . A large impact ionization coefficient ratio between that of electrons to holes was seen across a wide electric field range. Simulations of the avalanche multiplication in these structures using a random path length (RPL) model gave good agreement with experimental results over almost three orders of magnitude, and a mixed injection method was employed to verify the extracted impact ionization coefficients. Interestingly, no difference in the impact ionization coefficients was seen between digital alloy and random alloy Al 0.85 Ga 0.15 As 0.56 Sb 0.44 . This knowledge of impact ionization coefficients is beneficial for the future utilization of the Al x Ga 1-x As y Sb 1-y material system.
Digital alloy Al 0.85 Ga 0.15 As 0.56 Sb 0.44 , random alloy Al 0.85 Ga 0.15 As 0.56 Sb 0.44 , and random alloy Al 0.79 In 0.21 As 0.74 Sb 0.26 are promising candidates for the multiplication regions ...of avalanche photodiodes (APDs) due to their low excess noise, which is comparable to that of Si APDs. The temperature dependence of avalanche breakdown in these materials has been investigated by measuring the multiplication gain. A weak temperature dependence of the breakdown voltage is observed, which is desirable to reduce the complexity of temperature or reverse bias control circuits in the optical receiver. Calculations of the alloy disorder potentials and alloy scattering rates indicate that the temperature dependence of the avalanche breakdown in these quaternary alloys is attributable to the dominance of large mass variations and high alloy scattering over phonon scattering. Impact ionization can also be impacted by the temperature dependence of the bandgap energy which affects the ionization threshold energy. Therefore, the temperature dependence of the bandgap energy has been investigated by temperature-dependent photoluminescence and external quantum efficiency measurements to further explain the temperature dependent breakdown characteristics of these materials.
