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Advances in III-V semiconductor infrared absorbers and detectors
摘要： Advances in bulk III-V semiconductor material such as InGaAsSb and metamorphic InAsSb, as well as in a variety of type-II superlattices such as InGaAs/GaAsSb, InAs/GaSb, and InAs/InAsSb, have provided continuously adjustable cutoff wavelength coverage from the short to the very long wavelength infrared. We perform basic theoretical analysis to provide comparisons of different infrared materials. We also briefly report experimental results on a mid-wavelength InAs/InAsSb type-II superlattice unipolar barrier infrared detector and a focal plane array with significantly higher operating temperature than InSb.
关键词： unipolar barrier,MWIR,infrared detector,e-SWIR,LWIR,antimonide,type-II superlattice,nBn,effective mass
更新于2025-09-23 15:23:52
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Vibrational spectroscopic imaging and live cell video microscopy for studying differentiation of primary human alveolar epithelial cells
摘要： Alveolar type II(ATII) cells in the peripheral human lung spontaneously differentiate towards alveolar type I(ATI) cells, thus enabling air-blood barrier formation. Here, linear Raman and coherent anti-Stokes Raman scattering (CARS) microscopy are applied to study cell differentiation of freshly isolated ATII cells. The Raman spectra can successfully be correlated to gradual morphological and molecular changes during cell differentiation. Alveolar surfactant rich vesicles in ATII cells are identified based on phospholipid vibrations, while ATI-like cells are characterized by the absence of vesicular structures. Complementary, CARS microscopy allows for 3D visualization of lipid vesicles within ATII cells and their secretion, while hyperspectral CARS enables the distinction between cellular proteins and lipids according to their vibrational signatures. This study paves the path for further label-free investigations of lung cells and the role of the pulmonary surfactant, thus also providing a basis for rational development of future lung therapeutics.
关键词： confocal laser scanning microscopy,confocal Raman microscopy,pneumocyte type II differentiation,CARS microscopy,cell imaging
更新于2025-09-23 15:23:52
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Ultrathin 2D type-II p-n heterojunctions La2Ti2O7/In2S3 with efficient charge separations and photocatalytic hydrogen evolution under visible light illumination
摘要： In this work, novel 2D type-II p-n heterojunctions La2Ti2O7/In2S3 have been fabricated. The heterojunctions exhibit much improved photocatalytic activity over individual moieties and their physical mixtures in which 18-fold increment in hydrogen production has been achieved under visible light illumination (λ ≥ 400 nm). Their superior activities stem from intimate face-to-face contact between La2Ti2O7 and In2S3 in the heterojunctions which guarantee facile charge interchange. Photoelectrochemical analysis suggests that efficient charge separations occur at the interfaces of the heterojunctions and contributes to a prolonged charge lifetime as well as the much enhanced photocatalytic activities. Such a simple strategy by fabricating ultrathin type-II p-n heterojunctions also warrant promising applications in other areas such as optoelectronics, sensors etc. whereby efficient charge separations are needed.
关键词： charge separations,water splitting,type-II heterojunction,2D materials,photocatalyst
更新于2025-09-23 15:23:52
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WS <sub/>2</sub> /BSe van der Waals type-II heterostructure as a promising water splitting photocatalyst
摘要： The structure, electronic properties, charge transfer, band edge alignments and optical properties of WS2/BSe heterostructures are investigated by using first-principle calculations. Results imply that WS2/BSe heterostructures are semiconductor with an indirect energy gap (Egap) of 1.73 eV. Additionally, it has a feature of type-II band alignment, which contributes to spatial separation of photo-generated electron-hole pairs in WS2/BSe heterostructures. Charge transfer takes place from BSe to WS2 monolayers, which extends lifetime of the separated photo-induced charge carriers. Most importantly, band edges of the heterostructure are found to meet hydrogen evolution reaction (HER) in acid solutions (0 < pH < 7). Moreover, compared with only one for WS2 and BSe monolayers, the optical-absorption strength of the heterostructure is significantly enhanced and WS2/BSe heterostructures larges the range of absorption to 717 nm in the visible light region, improving the potential photocatalytic efficiency. These results explain the underlying mechanism of the enhanced photocatalytic activity of WS2/BSe heterostructures. Thus WS2/BSe heterostructures can be applied to 2D heterostructured photocatalysts.
关键词： type-II heterostructure,underlying mechanism,photocatalyst,WS2/BSe
更新于2025-09-23 15:23:52
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Design of InP Based High Speed Photodiode for 2 μm Wavelength Application
摘要： In this paper, we proposed and designed the high speed uni-traveling carrier photodiodes operating beyond 2 μm. InGaAs/GaAsSb type-II multiple quantum wells (MQWs) were used as the absorption region of uni-traveling carrier photodiode to have optical response beyond 2 μm. A rate equation model was developed to study the bandwidth characteristics of this photodiode. The carrier dynamics of the carrier sweeping out process was discussed, and the structure parameters of the quantum wells were optimized. Result shows a 3-dB bandwidth over 40 GHz can be achieved with the optimized design. We also studied the feasibility of dual depletion PIN (DD-PIN) photodiode with MQWs absorber. The optimized DD-PIN photodiode could achieve similar bandwidth under relatively high-bias condition.
关键词： high speed photodiodes,type-II quantum well,Carrier dynamic,uni-traveling carrier photodiode
更新于2025-09-23 15:22:29
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Electrical Properties of Midwave and Longwave InAs/GaSb Superlattices Grown on GaAs Substrates by Molecular Beam Epitaxy
摘要： In the present work, we report on the in-plane electrical transport properties of midwave (MWIR) and longwave infrared (LWIR) InAs/GaSb type-II superlattices (T2SLs) grown by molecular beam epitaxy (MBE) system on GaAs (001) substrate. The huge lattice mismatch between the T2SL and GaAs substrate is reduced by the growth of GaSb buffer layer based on interfacial misfit array (IMF) technique. In order to compensate the strain in the InAs/GaSb T2SL, we utilized a special shutters sequence to get InSb-like and GaAs-like interfaces. It is found that the MWIR InAs/GaSb T2SL exhibits a p- and n-type conduction at low and high temperatures, respectively. Interestingly, the conduction change temperature is observed to be dependent on the growth temperature. On the other hand, LWIR T2SL conduction is dominated only by electrons. It is important to note that the dominant scattering mechanism in LWIR T2SL at low temperatures is the interface roughness scattering mechanism.
关键词： Hall effect,High-resolution X-ray diffraction,Type-II superlattices,Molecular beam epitaxy
更新于2025-09-23 15:22:29
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Aneurysm Wall Enhancement Detected by Contrast Computed Tomography Scan Is Associated With Aneurysm Shrinkage After Endovascular Aneurysm Repair for Abdominal Aortic Aneurysm
摘要： Background: Aneurysm expansion, and consequent endoleaks, after endovascular aneurysm repair (EVAR) is a major problem. Accurate prediction of aneurysm expansion is demanding for surgeons and remains difficult. Methods and Results: We retrospectively analyzed 157 cases of EVAR for abdominal aortic aneurysm (AAA) using a bifurcated main-body stent-graft. There were 62 cases of aneurysm shrinkage after EVAR, 63 cases of stable aneurysm, and 32 cases of aneurysm expansion. Type I endoleaks were significantly increased in the aneurysm expansion group (EXP) compared with the stable (STB) and shrinkage (SHR) groups (EXP: 15.6% vs. STB: 4.8% vs. SHR: 0%, P=0.005). Type II endoleaks were also significantly increased in EXP (EXP: 65.6% vs. STB: 36.5% vs. SHR: 6.5%, P<0.001). Aneurysm wall enhancement (AWE) on imaging, however, was significantly decreased in the EXP group (EXP: 18.8% vs. STB: 23.8% vs. SHR: 53.2%, P<0.001). In multivariate analysis, the occurrence of type II endoleaks significantly decreased (P<0.001) and that of AWE significantly increased the likelihood of aneurysm shrinkage (P=0.032). Conclusions: AWE following EVAR may be associated with aneurysm shrinkage.
关键词： Endovascular aneurysm repair,Abdominal aortic aneurysm,Aneurysm wall enhancement,Type II endoleak,Retrospective cohort
更新于2025-09-23 15:22:29
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High-performance long-wavelength InAs/GaSb superlattice detectors grown by MOCVD
摘要： We demonstrate high-performance long-wavelength InAs/GaSb superlattice (SL) infrared photodetectors based on an Al-free single heterojunction grown by metalorganic chemical vapor deposition (MOCVD). The device structure consists of a mid-wavelength InAs/GaSb SL p-n junction (PN) and a long-wavelength InAs/GaSb SL n-type absorber (n), so-called PNn design, to reduce the dark current. In addition, a shallow etch technique was employed by exposing only mid-wavelength materials during pixel isolation to suppress surface leakage currents. At 77 K and a bias voltage of -0.1 V, the device exhibited a 50% cut-off wavelength at 8.0 μm, a dark current density of 2.4×10-5 A/cm2, and a peak responsivity of 2.1 A/W. Temperature dependent dark current measurement indicated diffusion-limited behavior down to 75 K. The specific detectivity was estimated to be 7.3×1011 cm·Hz1/2/W, which is comparable with that of detectors grown by molecular beam epitaxy (MBE) at similar cut-off wavelengths.
关键词： InAs/GaSb type-II superlattices,metalorganic chemical vapor deposition,heterostructure,long-wavelength infrared
更新于2025-09-23 15:22:29
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Nonlinear optical properties of core shell type II quantum dot structures
摘要： In this study, CdSe/CdTe Type-II quantum dots (QDs) were synthesized using dropwise method. The core/shell nanocrystals have been characterized by UV–Vis absorption and photoluminescence (PL) spectroscopies, transmission electron microscopy and z-scan technique. Nonlinear properties of each type of quantum dots were studied using femtosecond(fs) z-scan method at 800 nm wavelength with different laser intensities. Fs laser z-scan experimental set-up are used to determine two photon absorption coefficient (β ?10?12 cm/W) and nonlinear optical Kerr coefficient (n2 ? 10?20 cm2/W. The imaginary and real parts of third order susceptibility (X(3)) were calculated based on β and n2 under different laser intensities for seven different core/shell QDs. Third order susceptibility for CdSe/CdTe type II QDs was found to be about 10?12 esu.
关键词： Femtosecond Z-scan,CdSe/CdTe,Type-II quantum dots
更新于2025-09-23 15:21:01
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Highly Efficient Inorganic-Organic Heterojunction Solar Cells Based on Polymer and CdX (X=Se, Te) Quantum Dots: An Insight from a Theoretical Study
摘要： By using the density functional method, we explore the potentiality of recently synthesized CdX (X=Se, Te)QD/P3HT composites in solar energy conversion devices. Our study reveals that inorganic/organic hybrid CdXQD/P3HT nanocomposites with larger size of CdX QDs exhibit type-II band alignment, suggesting efficient charge separation upon photoexcitation. But for smaller size of QDs, the composites show type-I band alignment which are devoid of charge separation and thus are not suitable for solar cell applications. To remove this obstacle, we focus on chemical modification to polymer P3HT. The substitution of hydrogen at the beta position of each thiophene ring of polymer by electron withdrawing group (CN) results type-II band alignment and yield spatial charge separation even for smaller size of QDs. Finally, we calculated the powerconversion efficiency (PCE) of CdXQD and CN functionalized P3HT nanocomposites. The maximum calculated PCE value of 10.82% is achieved, which makes them immensely competitive with other reported heterojunction solar cells.
关键词： CdX (X=Se, Te)QD/P3HT composites,powerconversion efficiency,solar energy conversion,charge separation,type-II band alignment
更新于2025-09-23 15:21:01