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Diluted nitride type-II superlattices: Overcoming the difficulties of bulk GaAsSbN in solar cells
摘要： We demonstrate type-II GaAsSb/GaAsN superlattices (SL) as a suitable structure to form the lattice-matched 1.0–1.15 eV subcell that would allow the implementation of the optimum monolithic multi-junction solar cell design. The separation of Sb and N atoms during growth leads to an improved composition homogeneity and a lower defect density than in the bulk GaAsSbN counterparts. The type-II band alignment SLs provide long radiative lifetimes that facilitate carrier collection as compared to equivalent type-I SLs. Moreover, the radiative lifetime can be controllably tuned through the period thickness, which is not possible in type-I SLs. A reduced period thickness results in enhanced absorption due to increased wavefunction overlap, as well as in a change in the transport regime from diffusive to quasiballistic, providing improved carrier extraction efficiency. As a result, the short period SL single-junction solar cells show an enhanced power conversion efficiency of 134% over the equivalent bulk devices.
关键词： Strain-balanced,GaAsSbN,Type-II band Alignment,Multi-junction solar cells,Superlattices,1 eV bandgap
更新于2025-09-23 15:19:57
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Tailoring the photovoltaic effect in (1a??1a??1) oriented BiFeO <sub/>3</sub> /LaFeO <sub/>3</sub> superlattices
摘要： Ferroelectric and photovoltaic properties of (BiFeO3)(1?x)Λ/(LaFeO3)xΛ superlattices grown by pulsed laser deposition have been investigated (Λ being the bilayer thickness). For a high concentration of BiFeO3 a ferroelectric state is observed simultaneously with a switchable photovoltaic response. In contrast for certain concentration of LaFeO3 a non-switchable photovoltaic effect is evidenced. Such modulation of the PV response in the superlattices is attributed to the ferroelectric to paraelectric phase transition which is controlled with the increase of x. Remarkably, concomitant to this change of PV mechanism, a change of the conduction mechanism also seems to take place from a bulk-limited to an interface-limited transport as x increases.
关键词： photovoltaic effect,ferroelectrics,complex oxides,superlattices,multiferroics
更新于2025-09-23 15:19:57
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van der Waals heterostructures combining graphene and hexagonal boron nitride
摘要： As the first in a large family of 2D van der Waals (vdW) materials, graphene has attracted enormous attention owing to its remarkable properties. The recent development of simple experimental techniques for combining graphene with other atomically thin vdW crystals to form heterostructures has enabled the exploration of the properties of these so-called vdW heterostructures. Hexagonal boron nitride is the second most popular vdW material after graphene, owing to the new physics and device properties of vdW heterostructures combining the two. Hexagonal boron nitride can act as a featureless dielectric substrate for graphene, enabling devices with ultralow disorder that allow access to the intrinsic physics of graphene, such as the integer and fractional quantum Hall effects. Additionally, under certain circumstances, hexagonal boron nitride can modify the optical and electronic properties of graphene in new ways, inducing the appearance of secondary Dirac points or driving new plasmonic states. Integrating other vdW materials into these heterostructures and tuning their new degrees of freedom, such as the relative rotation between crystals and their interlayer spacing, provide a path for engineering and manipulating nearly limitless new physics and device properties.
关键词： quantum Hall effect,graphene,moiré superlattices,polaritons,hexagonal boron nitride,van der Waals heterostructures
更新于2025-09-19 17:15:36
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Efficient Algorithms for Optical Properties of Short Period Semiconductor Superlattices
摘要： This talk will deliver a review of a set of analytical equations for both luminescence and absorption of semiconductors, which have proven useful to describe dilute semiconductors. The algorithms can be a useful tool for superlattices and other effective three dimensional materials treated with the anisotropic medium approach.
关键词： luminescence,semiconductor superlattices,TERA-MIR
更新于2025-09-19 17:15:36
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Integral monolayer-scale featured digital-alloyed AlN/GaN superlattices using hierarchical growth units
摘要： Acquiring AlN/GaN digital alloys with matching coherent lattices, atomically sharp interfaces, and negligible compositional fluctuations remains a challenge. In this work, the nature and formation mechanism of the constituent elements of AlN and GaN atomic layers growth was examined by first-principle calculations and experimental demonstration. Basing on the calculated formation enthalpies, we developed a hierarchical growth method wherein AlN and GaN growth units are digitally stacked layer by layer through metal organic vapor-phase epitaxy, which involves the growth sequence instantaneously to control chemical potentials of the hierarchical growth units under different atmospheres. High-resolution X-ray diffraction and transmission electron microscopy confirmed that the hierarchical GaN and AlN growth units of digital-alloyed AlN/GaN structures had coherent lattices, abrupt interfaces, and integral monolayers at the atomic scale. The cathodoluminescence properties featured with single emission, combining with theoretical results, demonstrated that the capability of electronic energies via the digital-alloyed AlN/GaN superlattices. These results provide a basis toward the realization of other digital-alloyed nitride semiconductors.
关键词： digital-alloyed AlN/GaN superlattices,integral monolayer-scale,hierarchical growth units
更新于2025-09-19 17:15:36
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Superlattices are Greener on the Other Side: How Light Transforms Self-Assembled Mixed Halide Perovskite Nanocrystals
摘要： Perovskite nanocrystal superlattices (NC SLs) are the nearest real-world approximations to monodisperse NC ensembles. NC SLs thus represent ideal model systems for evaluating the optical and structural stability of CsPb(I1?xBrx)3 NCs at a macroscopic level. Here, photoinduced changes to CsPb(I1?xBrx)3 NC SLs (0 < x < 1.0) are probed via in situ photoluminescence, X-ray di?raction, and electron microscopy. We ?nd that prolonged (～10?20 h) ultraviolet?visible irradiation causes irreversible PL blueshifts, photobrightening, and crystal structure contractions. These changes stem from gradual photoinduced I2 sublimation, which transforms CsPb(I1?xBrx)3 into CsPbBr3. Despite eliminating half of the initial halides from individual CsPb(I0.53Br0.47)3 particles, NCs within SLs remarkably preserve their initial crystallinity, cuboidal shapes, edge lengths, and size distributions. This work illustrates compositional control toward generating precisely engineered perovskite NC SLs. It also highlights iodide photo-oxidation as a hurdle that must be overcome if mixed halide perovskite nanomaterials are to be applied beyond fundamental studies.
关键词： optical and structural stability,I2 sublimation,photoinduced changes,CsPb(I1?xBrx)3,Perovskite nanocrystal superlattices
更新于2025-09-19 17:13:59
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Spectral Shift of Quantum-Cascade Laser Emission under the Action of Control Voltage
摘要： Spectral redistribution of the intensity of short- and long-wavelength emission components within gain bandwidth of a 7- to 8-μ m quantum-cascade laser under the action of control voltage is demonstrated. As the voltage was increased from 10.5 to 18.2 V, the wavelength of maximum laser emission intensity shifted by approximately 200 nm. The maximum bandwidth of laser gain was about 300 nm (at a temperature of 80 K). The quantum-cascade laser heterostructure was grown by molecular beam epitaxy. The laser active region design was based on double-phonon depopulation of the lower level as implemented on In0.53Ga0.47As/In0.52Al0.48As heteropair of solid alloys lattice-matched with an InP substrate.
关键词： indium phosphide,quantum-cascade lasers,superlattices,epitaxy
更新于2025-09-16 10:30:52
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Design and Demonstration of High-Efficiency Quantum Well Solar Cells Employing Thin Strained Superlattices
摘要： Nanostructured quantum well and quantum dot III–V solar cells provide a pathway to implement advanced single-junction photovoltaic device designs that can capture energy typically lost in traditional solar cells. To realize such high-efficiency single-junction devices, nanostructured device designs must be developed that maximize the open circuit voltage by minimizing both non-radiative and radiative components of the diode dark current. In this work, a study of the impact of barrier thickness in strained multiple quantum well solar cell structures suggests that apparent radiative efficiency is suppressed, and the collection efficiency is enhanced, at a quantum well barrier thickness of 4 nm or less. The observed changes in measured infrared external quantum efficiency and relative luminescence intensity in these thin barrier structures is attributed to increased wavefunction coupling and enhanced carrier transport across the quantum well region typically associated with the formation of a superlattice under a built-in field. In describing these effects, a high efficiency (>26% AM1.5) single-junction quantum well solar cell is demonstrated in a device structure employing both a strained superlattice and a heterojunction emitter.
关键词： quantum well solar cells,III–V solar cells,strained superlattices,photovoltaic devices,high-efficiency
更新于2025-09-16 10:30:52
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Type-II superlattice photodetectors versus HgCdTe photodiodes
摘要： The development of the HgCdTe alloy as the most important intrinsic semiconductor for infrared (IR) technology is well established and recognized. In spite of the achievements in material and device quality, the drawbacks still exist due to bulk and surface instability, lower yields and higher costs particularly in fabrication of long wavelength infrared arrays. The dif?culties with this material encouraged to research on other compounds to improve device performance. Since the ?rst paper published by Sakaki and Esaki in 1978 it is well known that InAs and GaSb constitute a nearly lattice-matched material system offering great ?exibility in the design of IR optoelectronic devices. After four decades, the III-V type-II superlattice (T2SL) detector technology is under strong development as a possible alternative to HgCdTe. The novel ideas coming in design of detectors have enhanced the position of T2SLs in IR materials detector technology. It appears that T2SLs are especially helpful in the design of unipolar barriers. In this paper fundamental physical properties of two material systems, HgCdTe and T2SLs, are compared together with their in?uence on detector performance: dark current density, RA product, quantum ef?ciency, and noise equivalent different temperature. In comparison with HgCdTe, fundamental properties of T2SLs are inferior. On the other hand, T2SL and barrier detectors have several advantages to include lower tunnelling and surface leakage currents, and suppressed Auger recombination mechanism. Up to date, the promise of superior performance of these detectors has not been realized yet. In the paper we present that the performance of T2SL detectors (dark current, current responsivity, and noise equivalent difference temperature) is lower than bulk HgCdTe photodiodes. Due to stronger, less ionic chemical bonding of III-V semiconductors, these materials are attractive due to manufacturability and stability. It is also predicted that the interband T2SL quantum cascade devices will outperform the performance of the high operating temperature HgCdTe detectors.
关键词： Type-II superlattices,Responsivity,HgCdTe,Operability,Dark current,Interband cascade infrared detectors,Carrier lifetime
更新于2025-09-16 10:30:52
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Comparison of the Features of Electron Transport and Subterahertz Generation in Diodes Based on 6-, 18-, 70-, and 120-Period GaAs/AlAs Superlattices
摘要： A comparison of the features of electron transport in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a similar design is performed. However, the number of periods and diode areas are different. The values of the parasitic resistances of the near-contact diode regions are correlated, and the specific voltage drop across one superlattice period is determined for all special points in the current–voltage characteristics of the diodes. The mechanism of the appearance of stable current oscillations in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a high doping level is investigated.
关键词： diodes,THz generation,electron transport,superlattices
更新于2025-09-11 14:15:04