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.
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 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.
An imaging pixel unit-cell topology leveraging a photodetector in the forward-bias region is proposed. Connecting the anode of the photodiode to the gate of a NMOS device operating in the ...subthreshold region provides the basis for a new open-circuit voltage pixel (VocP) architecture. Theoretical analysis is presented to show the response and performance benefits of the VocP in comparison to a conventional pixel. Based on this analysis, the signal and noise relationships for both pixels are derived and leveraged to construct an end-to-end readout system model. The model results highlight potential performance benefits of the VocP over a conventional direct-injection pixel topology. To verify the analysis, the proposed VocP readout architecture is fabricated along with a conventional direct-injection pixel readout in a <inline-formula> <tex-math notation="LaTeX">0.18~\mathrm {\mu }\text{m} </tex-math></inline-formula> CMOS technology. The VocP performance is compared to a traditional reverse-bias current-mode photodetector configuration. Simulation, modeling, and measurements align with the proposed analytical model. Benefits in system sensitivity and dynamic range are demonstrated showing more than a <inline-formula> <tex-math notation="LaTeX">2\times </tex-math></inline-formula> improvement in noise-equivalent temperature difference and a 4 dB improvement in dynamic range.
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.
The increasing concentration of greenhouse gases, notably CH4 and CO2, has fueled global temperature increases, intensifying concerns regarding the prevailing climate crisis. Effectively monitoring ...these gases demands a detector spanning the extended short-wavelength infrared (~2.4 {\mu}m) range, covering wavelengths of CH4 (1.65 {\mu}m) and CO2 (2.05 {\mu}m). The state-of-the-art HgCdTe avalanche photodetectors (APDs) offer exceptional performance metrics, including high gain (M) and low excess noise (F). However, their widespread adoption is hindered by inherent challenges such as manufacturability, reproducibility, and cost factors. Moreover, their reliance on cryogenic cooling adds to the cost, size, weight, and power of the system. We have demonstrated a linear mode APD combining an InGaAs/GaAsSb type-II superlattice absorber and an AlGaAsSb multiplier lattice matched to InP substrates. This APD has demonstrated a room temperature M of 178, a maximum measurable external quantum efficiency of 3560 % at 2 {\mu}m, an extremely low excess noise (F < 2 at M < 20), and a small temperature coefficient of breakdown (7.58 mV/K {\mu}m). Such a high performance APD with manufacturable semiconductor materials could lead to a rapid transition to a commercial III-V foundry, holding the promise of revolutionizing high-sensitivity receivers for greenhouse gas monitoring.
We have demonstrated InGaAs/AlInAsSb separate absorption, charge, and multiplication avalanche photodiodes. The multiplication gain, excess noise, and temperature-dependent dark current have been ...characterized. InGaAs/AlInAsSb APDs were grown on semi-insulating InP substrates, which is beneficial for bandwidth improvement compared to AlInAsSb APDs grown on GaSb substrates.
This work demonstrates the use of aluminum oxide passivation on the mesa sidewall of long-wave infrared p-type superlattice photodetectors applied by atomic layer deposition. The surface leakage ...current of the passivated photodetectors was reduced by an order of magnitude over the unpassivated photodetectors.
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