We developed an x-ray diffraction (XRD) method that uses relative satellite peak intensities to assess the width of the alloy interfaces in InAs/InAsSb Type 2 superlattices (T2SLs). Specifically, our ...method simulates XRD patterns for T2SLs based on a model of alloy cross-incorporation and fits the simulated pattern to experimental data through a small set of model parameters. We model the Sb distribution function with two forms (i) a Gaussian function, or (ii) two error functions. We compared the model with experimental data extracted from the literature. The first example is a T2SL with 50 periods of 7.0 nm thick InAs and 2.3 nm thick InAs
1-x
Sb
x
with the targeted alloy composition of x = 0.23. The second example is a T2SL with 100 periods of 4.6 nm thick InAs and 1.7 nm thick InAs
1-x
Sb
x
with the targeted composition of x = 33.3%. The width of the alloy interface is about 2.54 nm for the first example with the Gaussian model, and with the error function model is 2.8 nm. In the second example, we observed a lower width of the alloy interface of about 0.48 nm with the Gaussian model, and 0.5 nm with the error function model.
We report a novel dual-band barrier infrared detector (DBIRD) design using InAs/GaSb type-II superlattices (T2SLs). The DBIRD structure consists of back-to-back barrier diodes: a “blue channel” (BC) ...diode which has an nBp architecture, an n-type layer of a larger bandgap for absorbing the blue band infrared/barrier/p-type layer, and a “red channel” (RC) diode which has a pBn architecture, a p-type layer of a smaller bandgap for absorbing the red band infrared/barrier/n-type layer. Each has a unipolar barrier using a T2SL lattice matched to a GaSb substrate to impede the flow of majority carriers from the absorbing layer. Each channel in the DBIRD can be independently accessed with a low bias voltage as is preferable for high-speed thermal imaging. The device modeling of DBIRDs and simulation results of the current–voltage characteristics under dark and illuminated conditions are also presented. They predict that the dual-band operation of the DBIRD will produce low dark currents and 45–56% quantum efficiencies for the in-band photons in the BC with λc = 5.58 μm, and a nearly constant 32% in the RC with λc = 8.05 μm. The spectral quantum efficiency of the BC for 500 K blackbody radiation is approximately 50% over the range of λ = 3–4.7 μm, while that of the RC has a peak of 42% at 5.9 μm. The DBIRD may provide improved high-speed dual-band imaging in comparison with NBn dual-band detectors.
In this study, a plausible separate absorption and multiplication infrared avalanche photodiode (SAM IR APD) with HgCdTe heterojunctions was investigated, including a design method and a comparative ...study of multiplication layer (ML) designs. The selection of wavelength to be detected determines the energy bandgap of the absorption layer (AL). After this, there are two choices of the ML to make a SAM IR APD, one a larger bandgap material and the other smaller. In this study, electrostatic analysis, dark current modeling and simulation were performed on MWIR detecting HgCdTe APDs with three choices of the MLs. It is shown that the SAM IR APD with the larger band gap ML could provide great advantages in terms of extremely low dark current and high sensitivity. Hence, a SAM IR APD with larger bandgap ML can be used to realize high sensitivity and extremely low power IR APDs that are preferred for future applications.
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.
HgTe-based colloidal quantum dots (CQDs) fabricated between 10 nm and 20 nm in size readily lead to infrared cutoff wavelengths between 3
μ
m and 12
μ
m, due to their quantum confinement. In ...previous work, infrared photodetection using these films has been demonstrated to detect radiation out to a wavelength of 12
μ
m, and imaging in the mid-wave infrared region. In this work, a complete focal plane array and imager was fabricated and its performance measured for detecting radiation out to 12
μ
m. The photoconductive and optical properties of these HgTe CQD films are described, along with recent advancements in CQD detector technology. Anticipated improvements in the CQD synthesis and film deposition chemistries and techniques can raise the specific detectivity of these CQD films, bringing them closer to room-temperature operation.
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.
Type-II strained layer superlattices (SLSs) offer a broad range of design degrees of freedom to help optimize their properties as absorber layers of infrared photon detectors. We theoretically ...examine a new class of mid-wavelength infrared (2-5 μm bandpass) Type-II structures with two-layer InGaSb/InPSb and four-layer InAs/GaSb/InAs/InPSb SLS periods. Phosphorous-containing SLSs are a promising approach to improving infrared photon detector performance due to providing a new set of material properties, including favorable valence band offsets. P-based SLSs of four-layer type InAs/GaSb/InAs/InPSb were found to be among the best 5-μm gap SLSs that we have modeled. Among the studied designs, the lowest dark current in an ideal structure is predicted for a four-layer 23.6 Å InAs/20 Å GaSb/23.6 Å InAs/60 Å InP 0.62 Sb 0.38 SLS. Its predicted ideal dark current is about 35 times lower than an n-type HgCdTe-based photodiode absorber and six times lower than a p-type HgCdTe one for the same bandgap, temperature, and dopant concentration. We also discuss a defect mitigation strategy that involves positioning the SLS gap in an energy range that avoids defect levels and show how this applies to the aforementioned P-containing SLS.
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