Madison E. Woodson

Low-noise AlInAsSb avalanche photodiode

We report low-noise avalanche gain from photodiodes composed of a previously uncharacterized alloy, Al0.7In0.3As0.3Sb0.7, grown on GaSb. The bandgap energy and thus the cutoff wavelength are similar to silicon; however, since the bandgap of Al0.7In0.3As0.3Sb0.7 is direct, its absorption depth is 5 to 10 times shorter than indirect-bandgap silicon, potentially enabling significantly higher operating bandwidths. In addition, unlike other III-V avalanche photodiodes that operate in the visible or near infrared, the excess noise factor is comparable to or below that of silicon, with a k-value of approximately 0.015. Furthermore, the wide array of absorber regions compatible with GaSb substrates enable cutoff wavelengths ranging from 1 μm to 12 μm.

AlInAsSb separate absorption, charge, and multiplication avalanche photodiodes

We report Al<inf>x</inf>In<inf>1−x</inf>Asj, Sb<inf>1−y</inf>-based separate absorption, charge, and multiplication avalanche photodiodes (APDs) that operate in the short-wavelength infrared spectrum. These APDs exhibit low excess noise factor, corresponding to k = 0.01, and low dark current.

AlInAsSb/GaSb staircase avalanche photodiode

Over 30 years ago, Capasso and co-workers [IEEE Trans. Electron Devices 30, 381 (1982)] proposed the staircase avalanche photodetector (APD) as a solid-state analog of the photomultiplier tube. In this structure, electron multiplication occurs deterministically at steps in the conduction band profile, which function as the dynodes of a photomultiplier tube, leading to low excess multiplication noise. Unlike traditional APDs, the origin of staircase gain is band engineering rather than large applied electric fields. Unfortunately, the materials available at the time, principally AlxGa1−xAs/GaAs, did not offer sufficiently large conduction band offsets and energy separations between the direct and indirect valleys to realize the full potential of the staircase gain mechanism. Here, we report a true staircase APD operation using alloys of a rather underexplored material, AlxIn1−xAsySb1−y, lattice-matched to GaSb. Single step “staircase” devices exhibited a constant gain of ∼2×, over a broad range of applied ...

Toward deterministic construction of low noise avalanche photodetector materials

Over the past 40+ years, III-V materials have been intensively studied for avalanche photodetectors, driven by applications including optical communications, imaging, quantum information processing, and autonomous vehicle navigation. Unfortunately, impact ionization is a stochastic process that introduces noise, thereby limiting sensitivity and achievable bandwidths, leading to intense effort to mitigate this noise through the identification of different materials and device structures. Exploration of these materials has seen limited success as it has proceeded in a largely ad hoc fashion due to little consensus regarding which fundamental properties are important. Here, we report an exciting step toward deterministic design of low-noise avalanche photodetector materials by alternating the composition at the monolayer scale; this represents a dramatic departure from previous approaches, which have concentrated on either unconventional compounds/alloys or nanoscale band-engineering. In particular, we demonstrate how to substantially improve upon the noise characteristics of the current state-of-the art telecom avalanche multipliers, In0.52Al0.48As grown on InP substrates, by growing the structure as a strain-balanced digital alloy of InAs and AlAs layers, each only a few atomic layers thick. The effective k-factor, which has historically been considered a fundamental material property, was reduced by 6–7× from k = 0.2 for bulk In0.52Al0.48As to k = 0.05 by using the digital alloy technique. We also demonstrate that these “digital alloys” can significantly extend the photodetector cutoff wavelength well beyond those of their random alloy counterparts.Over the past 40+ years, III-V materials have been intensively studied for avalanche photodetectors, driven by applications including optical communications, imaging, quantum information processing, and autonomous vehicle navigation. Unfortunately, impact ionization is a stochastic process that introduces noise, thereby limiting sensitivity and achievable bandwidths, leading to intense effort to mitigate this noise through the identification of different materials and device structures. Exploration of these materials has seen limited success as it has proceeded in a largely ad hoc fashion due to little consensus regarding which fundamental properties are important. Here, we report an exciting step toward deterministic design of low-noise avalanche photodetector materials by alternating the composition at the monolayer scale; this represents a dramatic departure from previous approaches, which have concentrated on either unconventional compounds/alloys or nanoscale band-engineering. In particular, we demon...

Al x in 1-x as y sb 1-y separate absorption, charge, and multiplication avalanche photodiodes

The authors report SACM APDs fabricated from AlxIn1-xAsySb1-y, grown on GaSb. The excess noise factor is characterized by a k value of 0.01, which is comparable to or below that of Si APDs. These APDs response to wavelength beyond 1600 nm and achieved gains >90x. These APDs combine the excellent gain/noise characteristics of Si with the low dark current and promising high speed of the III-V compound APDs.

Low-noise high-gain tunneling staircase photodetector

Avalanche photodiodes (APD) are important components in short-wave and mid-wave infrared detection systems (imaging, laser radar, communications, etc.) because their internal gain can improve receiver sensitivity and enable the detection of weak photon fluxes. However, gain originates from impact ionization, a stochastic process that results in excess noise and limits the gain-bandwidth product. The staircase APD was proposed as the solid-state analog of the photomultiplier tube where impact ionization events occur proximate to the sharp bandgap discontinuity of each step. As a result, the gain process is more deterministic, with concomitant reduction in gain fluctuations and, thus, lower excess noise. An additional advantage of the staircase structure is that the kinetic energy change required to initiate impact ionization events is supplied by band engineering and a modest applied field, rather than large bias, which is typically 10s of Volts for conventional APDs. Unfortunately, initial studies of staircase APDs used the AlxGai_xAs material system, which has inadequate band offsets and the projected noise characteristics were never achieved, We recently demonstrated the first staircase APDs, where a single step exhibits a constant gain of ~2x over a range of bias, temperature, and excitation wavelength, enabled by the digital alloy growth of high-quality AlInAsSb, lattice-matched to GaSb across the full range of direct bandgap compositions.

Recent progress in avalanche photodiodes for sensing in the IR spectrum

Abstract—We report low-noise avalanche gain from photodiodes composed of a previously uncharacterized alloy, AlxIn1-xAsySb1-y, grown lattice-matched on GaSb substrates. By varying the aluminum content the direct bandgap can be tuned from 0.25 eV (0% aluminum) to 1.24 eV (75% aluminum), corresponding to photon wavelengths from 5000 nm to 1000 nm, with the transition from direct-gap to indirect-gap occurring at ~1.18 eV (~72% aluminum), or 1050 nm. This has been used to fabricate separate absorption, charge, and multiplication (SACM) APDs using Al0.7In0.3As0.3Sb0.7 for the multiplication region and Al0.4In0.6As0.3Sb0.7 for the absorber. Gain values as high as 100 have been achieved and the excess noise factor is characterized by a k value of 0.01, which is comparable to or below that of Si. In addition, since the bandgap of the absorption region is direct, its absorption depth is 5 to 10 times shorter than indirect-bandgap silicon, potentially enabling significantly higher operating bandwidths.

Low excess noise AlInAsSb staircase avalanche photodiode

In conclusion, we report a one-stage staircase APD based on the AlInAsSb material system. Record low noise has been achieved for the first time and the results are consistent with Monte Carlo simulations.