We report focal plane array (FPA) results on a mid-wavelength InAs/InAsSb type-II strained layer superlattice (T2SLS) unipolar barrier infrared detector with a cutoff wavelength of 5.4 μm. For 300 K ...background in the 3-5-μm band, f/2 aperture, an FPA operating at 150 K exhibits a mean noise equivalent differential temperature (NEDT) of 18.5 mK, and an NEDT operability of 99.7%. The NEΔT distribution has a width of 8 mK, with no noticeable distribution tail, indicating excellent uniformity. The mean noise-equivalent irradiance is 9.1 × 10 11 photons/sec-cm 2 . The mean quantum efficiency is 49.1% without antireflection coating, and the mean specific detectivity (D * ) is 2.53 × 10 11 cm-Hz ½ /W. Benefitting from an absorber material with a much longer Shockley-Read-Hall minority carrier lifetime, and a device architecture that suppresses generation-recombination and surface-leakage dark current, the InAs/InAsSb T2SLS barrier infrared detector FPA has demonstrated a significantly higher operating temperature than the mid-wavelength infrared market-leading InSb.
The InAs/InAsSb (Gallium-free) type-II strained-layer superlattice (T2SLS) has emerged in the last decade as a viable infrared detector material with a continuously adjustable band gap capable of ...accommodating detector cutoff wavelengths ranging from 4 to 15 µm and beyond. When coupled with the unipolar barrier infrared detector architecture, the InAs/InAsSb T2SLS mid-wavelength infrared (MWIR) focal plane array (FPA) has demonstrated a significantly higher operating temperature than InSb FPA, a major incumbent technology. In this brief review paper, we describe the emergence of the InAs/InAsSb T2SLS infrared photodetector technology, point out its advantages and disadvantages, and survey its recent development.
Cushing’s disease (CD) is a rare and severe endocrine disease characterized by hypercortisolemia. Previous studies have found structural brain alterations in remitted CD patients compared to healthy ...controls, specifically in the anterior cingulate cortex (ACC). However, potential mechanisms through which these persistent alterations may have occurred are currently unknown.
Structural 3T MRI’s from 25 remitted CD patients were linked with gene expression data from neurotypical donors, derived from the Allen Human Brain Atlas. Differences in gene expression between the ACC and an unaffected control cortical region were examined, followed by a Gene Ontology (GO) enrichment analysis. A cell type enrichment analysis was conducted on the differentially expressed genes, and a disease association enrichment analysis was conducted to determine possible associations between differentially expressed genes and specific diseases. Subsequently, cortisol sensitivity of these genes in existing datasets was examined.
The gene expression analysis identified 300 differentially expressed genes in the ACC compared to the cortical control region. GO analyses found underexpressed genes to represent immune function. The cell type specificity analysis indicated that underexpressed genes were enriched for deactivated microglia and oligodendrocytes. Neither significant associations with diseases, nor evidence of cortisol sensitivity with the differentially expressed genes were found.
Underexpressed genes in the ACC, the area vulnerable to permanent changes in remitted CD patients, were often associated with immune functioning. The specific lack of deactivated microglia and oligodendrocytes implicates protective effects of these cell types against the long-term effects of cortisol overexposure.
•Underexpressed genes in the ACC of CD patients associated with immune functioning.•Fewer deactivated microglia and oligodendrocytes markers in the ACC of CD patients.•These cell types may protect against the effects of chronic cortisol overexposure.
Epitaxially grown self-assembled InAs-InGaAs-GaAs quantum dots (QDs) are exploited for the development of large-format long-wavelength infrared focal plane arrays (FPAs). The dot-in-a-well (DWELL) ...structures were experimentally shown to absorb both 45deg and normal incident light, therefore, a reflection grating structure was used to enhance the quantum efficiency. The devices exhibit peak responsivity out to 8.1 mum, with peak detectivity reaching ~1times10 super(10) Jones at 77 K. The devices were fabricated into the first long-wavelength 640times512 pixel QD infrared photodetector imaging FPA, which has produced excellent infrared imagery with noise equivalent temperature difference of 40 mK at 60-K operating temperature
A free space optical (FSO) link utilizing midinfrared (mid-IR) interband cascade lasers has been demonstrated in the 3- to 5-¿m atmospheric transmission window with data rates up to 70 Mb/s and ...bit-error rate (BER) less than 10 -8 . The performance of the mid-IR FSO link has been compared with the performance of a near-IR link under various fog conditions using an indoor communication testbed. These experiments demonstrated the lower attenuation and scintillation advantages of a mid-IR FSO link.
We describe the challenges for long- and very long-wavelength InAs/InAsSb type-II strained-layer superlattice infrared detectors, and provide an overview of progress in device architecture ...development for addressing them. Specifically, we have explored the complementary barrier infrared detector (CBIRD) that contains p-type InAs/InAsSb T2SLS absorbers for enhancing quantum efficiency, while also suppressing surface shunt current. We describe selected device results, and also provide references to additional results and more in-depth discussions.
Long-wavelength complementary barrier infrared detector (CBIRD) based on III-V material is hybridized to recently designed and fabricated 320 × 256 pixel format two-color read-out integrated circuit. ...The n-type CBIRD is characterized in terms of performance and thermal stability. This paper reports on the measured dark current density, noise equivalent difference temperature, quantum efficiency, responsivity, minimum resolvable difference temperature, and modulation transfer function.
A limitation to the advancement of the strained-layer superlattice technology for infrared detection is unwanted high dark currents and low
R
0
A values, especially at long-wavelengths. In this ...paper, we discuss dark current characteristics of LWIR InAs/GaSb type-II superlattice detectors. Comparing devices with different dominant mechanisms, a more thorough analysis at low temperatures is provided.
While the
n
-type InAs/InAsSb type-II strained layer superlattice (T2SLS) has demonstrated excellent detector and focal plane array performance in the mid-wavelength infrared, it is limited in its ...attainable quantum efficiency (QE) in the long and very long wavelength infrared due to short hole diffusion length and modest absorption coefficient. We explore InAs/InAsSb T2SLS unipolar barrier infrared detectors that contain
p
-type absorber layers in order to take advantage of the longer electron diffusion length for QE enhancement. We find that while they can achieve enhanced QE, their dark current characteristics are affected by the presence of metallurgical and surface
p
-
n
junctions, and are best operated under lower biasing conditions where the tunneling dark currents are less pronounced. We report results on complementary barrier infrared detector structures that use
n
-type absorbers, a combination of
p
- and
n
-type absorbers, and
p
-type absorbers, with cutoff wavelengths ranging from 10.0 µm to 15.3 µm.
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