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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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Nitrogen mapping from ADF imaging analysis in quaternary dilute nitride superlattices
摘要： A method for the determination of N distribution in dilute nitride GaAsSbN superlattices (SLs) by using different STEM imaging settings is proposed. The method combines the simultaneous acquisition under Low Angle (LA-) and High Angle (HA-) Annular Dark Field (ADF) conditions by exploiting two different dedicated angle intervals. On one hand, HAADF technique gives information that principally depends on the atomic number (Sb sensitive) and on the other hand, N atoms produce high static atomic displacements affecting the image intensity especially under LAADF conditions. However, the simultaneous presence of Sb and N supposes an important handicap to differentiate both elements. N distribution maps could be obtained from suitable normalization and the separation of the intensity ratios in regions with/without Sb. Semi-quantitative maps are also available by combination of the results from high-resolution X-ray diffraction and energy dispersive X-Ray spectroscopy techniques. Type-I (GaAsSbN/GaAs) and type-II (GaAsSb/GaAsN) SL structures are evaluated using the proposed methodology. Differences in the N distribution between both samples such as inhomogeneities and cluster formation are discussed. Specifically, we have found a greater number of N-rich regions in type-I structure as compared to their type-II counterparts, which could have an influence on the optical response of each design.
关键词： STEM,Dilute nitride,Compositional distribution,Superlattice structures
更新于2025-09-23 15:22:29
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From Lead Iodide to Radical Form Lead-Iodide Superlattice: High Conductance Gain and Broader Band for Photoconductive Response
摘要： Superlattice materials offer new opportunities to modify optical and electrical properties of the recently emerging 2D materials. The insertion of tetraethylbenzidine into interlamination of the known 2D PbI2 semiconductor through a mild solution method yielded lead-iodide superlattice, EtDAB·4PbI2 (EtDAB = tetraethylbenzidine), with radical and non-radical forms. The non-radical form has a nonionic structure that differs from the common ionic structures for inorganic–organic hybrid lead halides. The radical form shows five orders of magnitude of conductance gain and broader photoconductive response range (UV–Vis → UV–Vis–IR), compared with pure PbI2 and the non-radical form.
关键词： Inorganic-organic hybrid,Photoconductive,Semiconductive,Lead halide,Superlattice
更新于2025-09-23 15:22:29
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From Lead Iodide to Radical Form Lead-Iodide Superlattice: High Conductance Gain and Broader Band for Photoconductive Response
摘要： Superlattice materials offer new opportunities to modify optical and electrical properties of the recently emerging 2D materials. The insertion of tetraethylbenzidine into interlamination of the known 2D PbI2 semiconductor through a mild solution method yielded lead-iodide superlattice, EtDAB·4PbI2 (EtDAB = tetraethylbenzidine), with radical and non-radical forms. The non-radical form has a nonionic structure that differs from the common ionic structures for inorganic–organic hybrid lead halides. The radical form shows five orders of magnitude of conductance gain and broader photoconductive response range (UV–Vis → UV–Vis–IR), compared with pure PbI2 and the non-radical form.
关键词： Inorganic-organic hybrid,Photoconductive,Semiconductive,Lead halide,Superlattice
更新于2025-09-23 15:22:29
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Interface intermixing and interdiffusion characteristics in MOVPE grown spontaneous AlxGa1-xAs/GaAs (100) superlattice structures using high resolution X-ray diffraction
摘要： Thermal diffusion characteristics in naturally grown ultra-nanoscale superlattice structures have been studied. In absence of any suitable direct experimental tool due to the physical resolution limit, here we rely on the theoretical analysis of x-ray rocking curve simulations coupled with the diffusion equation to arrive at the diffusion characteristics across the interfaces of spontaneously grown AlGaAs/AlGaAs superlattice structures. The simulation approach presented here is a combination of a virtual interdiffusion code and a code on x-ray diffraction. We have obtained the variation in the actual diffusion coefficient as a function of time at different temperatures from the decay rates of the integrated satellite peak intensities. We have also found the diffusion coefficient to be highly nonlinear across the interface with time. The satellite decay equation could fit the experimental data taking the maximum Al composition alone at each time step. The pre exponential factor and the activation enthalpy values for interdiffusion are found out to be 0.17-0.25 cm2 /s and 0.5-0.6 eV for Al diffusion whereas 0.01-0.11 cm2/s and 3.45-3.5 eV for Ga diffusion, respectively in the studied temperature range of 500 oC to 700 oC. The interdiffusivity increases with temperature from 500 oC to 625 oC and decreases for further rise in temperature as the compositional contrast between the two layers decreases significantly at higher temperatures.
关键词： MOVPE,Interdiffusion,HTXRD,AlxGa1-xAs,Spontaneous superlattice
更新于2025-09-23 15:22:29
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Accurate Gap Determination in Monolayer and Bilayer Graphene/h-BN Moiré Superlattices
摘要： High mobility single and few-layer graphene sheets are in many ways attractive as nanoelectronic circuit hosts but lack energy gaps, which are essential to the operation of field-effect transistors. One of the methods used to create gaps in the spectrum of graphene systems is to form long period moiré patterns by aligning the graphene and hexagonal boron nitride (h-BN) substrate lattices. Here, we use planar tunneling devices with thin h-BN barriers to obtain direct and accurate tunneling spectroscopy measurements of the energy gaps in single- and bi-layer graphene-h-BN superlattice structures at charge neutrality (first Dirac point) and at integer moiré band occupancies (second Dirac point, SDP) as a function of external electric and magnetic fields and the interface twist angle. In single-layer graphene we find, in agreement with previous work, that gaps are formed at neutrality and at the hole-doped SDP, but not at the electron-doped SDP. Both primary and secondary gaps can be determined accurately by extrapolating Landau fan patterns to zero magnetic field and are as large as ≈ 17 meV for devices in near perfect alignment. For bilayer graphene, we find that gaps occur only at charge neutrality where they can be modified by an external electric field.
关键词： graphene-h-BN moiré superlattice,Landau level tunneling spectroscopy,bilayer graphene-h-BN superstructure,high-precision measurement,graphene energy gap
更新于2025-09-23 15:21:21
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Minority carrier lifetime and diffusion length in type II superlattice barrier devices
摘要： The minority carrier lifetime in p-type InAs/GaSb type II superlattices (T2SLs) is quite short, typically in the region of tens of nanoseconds. In spite of this, T2SLs are becoming a viable alternative to Mercury Cadmium Telluride as the sensing material of choice for high end MWIR and LWIR infrared detectors. For example, SCD now manufactures a 640 × 512 format, 15 μm pitch LWIR focal plane array detector, with a quantum e?ciency close to 50%, a pixel operability of > 99.5%, and a dark current only about one order of magnitude larger than the state of the art Rule 07 value. A key to the very high performance of this detector is the use of an XBp barrier architecture that both suppresses the G-R current and allows stable passivation to all steps of the fabrication process. Since both the dark-current and photo-current in the XBp structure are di?usion limited, measurements of these quantities as a function of the device dimension provide an excellent vehicle for estimating the minority carrier lifetime and di?usion length, when performed in conjunction with k?p calculations of the T2SL density of states. Typical lifetime results are presented, which are consistent with values found by others using direct measurements. Di?usion lengths are reported in the range 3–7 μm, although these are not necessary limiting values.
关键词： Type II superlattice,Infrared detector,XBp detector,Di?usion length,InAs/GaSb superlattice,K?p model,Lifetime,Bariode
更新于2025-09-23 15:21:01
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The coupled dynamics of colloidal nanoparticle spreading and self-assembly at a fluid-fluid interface
摘要： We investigated the physicochemical and transport phenomena governing the self-assembly of colloidal nanoparticles at the interface of two immiscible fluids. By combining in-situ grazing incidence small-angle X-ray scattering (GISAXS) with a temporal resolution of 200 ms and electron microscopy measurements we gained new insights into the coupled effects of solvent spreading, nanoparticle assembly and recession of the vapor-liquid interface on the morphology of the self-assembled thin films. We focus on oleate-passivated PbSe nanoparticles dispersed across an ethylene glycol subphase as a model system and demonstrate how solvent parameters such as surface tension, nanoparticle solubility, aromaticity and polarity influence the mesoscale morphology of the nanoparticle superlattice. We discovered that a nanoparticle precursor monolayer film spreads in front of the bulk solution and influences the fluid spreading across the subphase. Improved understanding of the impact of kinetic phenomena (i.e., solvent spreading and evaporation) on superlattice morphology is important to describe the formation mechanism and ultimately enable assembly of high-quality superlattices with long range order.
关键词： self-assembly,interfacial phenomena,in-situ GISAXS,nanoparticle superlattice,spreading dynamics
更新于2025-09-23 15:21:01
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Binary Superlattices of Infrared Plasmonic and Excitonic Nanocrystals
摘要： Self-assembled superlattices of nanocrystals offer exceptional control over the coupling between nanocrystals, similar to how solid-state crystals tailor the bonding between atoms. By assembling nanocrystals of different properties (e.g., plasmonic, excitonic, dielectric, or magnetic), we can form a wealth of binary superlattice metamaterials with new functionalities. Here, we introduce infrared plasmonic Cu2?xS nanocrystals to the limited library of materials that have been successfully incorporated into binary superlattices. We are the first to create a variety of binary superlattices with large excitonic (PbS) nanocrystals and small plasmonic (Cu2?xS) nanocrystals, both resonant in the infrared. Then, by controlling the surface chemistry of large Cu2?xS nanocrystals, we produced structurally analogous superlattices of large Cu2?xS and small PbS nanocrystals. Transmission electron microscopy (TEM) and grazing-incidence small-angle X-ray scattering (GISAXS) were used to characterize both types of superlattices. Furthermore, our unique surface modification of the large Cu2?xS nanocrystals also prevented them from chemically quenching the photoluminescence of the PbS nanocrystals, which occurred when the PbS nanocrystals were mixed with unmodified Cu2?xS nanocrystals. These synthetic achievements create a set of binary superlattices that can be used to understand how infrared plasmonic and excitonic nanocrystals couple in a variety of symmetries and stoichiometries.
关键词： infrared quantum dots,nanocrystals,self-assembly,supracrystal,metamaterial,binary superlattice,grazing-incidence small-angle X-ray scattering (GISAXS)
更新于2025-09-23 15:21:01
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AlInGaN-based superlattice p-region for improvement of performance of deep UV LEDs
摘要： A deep ultraviolet light-emitting diode (DUV LED) consisting of a specifically designed intermediate p-type region involving a superlattice quaternary nitride alloy has been proposed. The light output power of the proposed structure has been found significantly large; around 28.30 times high in comparison to the conventional structure, at the current density of 200 A/cm2. The maximum internal quantum efficiency of the proposed structure is 153.63% higher compared to the conventional one. Moreover, the efficiency droop has been reduced by 99.08%. Absence of abrupt potential barrier owing to the strain compensation provided by the superlattice p-AlInGaN layer offers an attractive solution for enhancing the hole injection into the active region leading to the improvement in performance of DUV LED.
关键词： Efficiency droop,Superlattice-AlInGaN,Strain compensation,DUV LED
更新于2025-09-23 15:21:01