Journal articles: 'Superlattices'

1

Fullerton, Eric E., Ivan K. Schuller, and Y. Bruynseraede. "Quantitative X-Ray Diffraction From Superlattices." MRS Bulletin 17, no. 12 (December 1992): 33–38. http://dx.doi.org/10.1557/s0883769400046935.

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The physical properties of superlattices have been the subject of considerable interest because a wide range of phenomena associated with very thin films, interfaces, and coupling effects can be studied. Recent areas of activity in metallic superlattices include antiferromagnetic coupling of ferromagnetic layers across nonmagnetic spacer layers, giant magnetoresistance, magnetic surface anisotropy, low-dimensional superconductivity, and anomalous mechanical properties. All of these phenomena are strongly affected by the chemical and physical properties of the individual layers and by the superlattice structure. Therefore, a detailed understanding of the properties of superlattices requires a nondestructive, quantitative determination of the superlattice structure.Because superlattices are not in thermodynamic equilibrium, their structure is sensitive to preparation methods and growth conditions. A dramatic example of superlattice structural dependence on growth conditions is shown in Figure 1, for sputtered Nb/Si superlattices. Increasing the Ar pressure during sputtering decreases the kinetic energy of the deposited atoms, thereby changing their surface mobility, and thus altering growth dynamics. Figure 1 shows the low-angle x-ray diffraction and cross-sectional transmission electron microscopy (TEM) images of [Nb(35 Å)/Si(25 Å)]40, superlattices sputtered in, respectively, 3 and 15 mTorr of Ar. The TEM image of the 3 mTorr superlattice clearly shows the smooth and continuous layering across the entire cross section of the image (≈5 μm). This is characteristic of sputtered metal/semiconductor superlattices used for x-ray optics.

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2

Hansen, Monica, Amber C. Abare, Peter Kozodoy, Thomas M. Katona, Michael D. Craven, Jim S. Speck, Umesh K. Mishra, Larry A. Coldren, and Steven P. DenBaars. "Effect Of AlGaN/GaN Strained Layer Superlattice Period On InGaN MQW Laser Diodes." MRS Internet Journal of Nitride Semiconductor Research 5, S1 (2000): 14–19. http://dx.doi.org/10.1557/s1092578300004026.

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AlGaN/GaN strained layer superlattices have been employed in the cladding layers of InGaN multi-quantum well laser diodes grown by metalorganic chemical vapor deposition (MOCVD). Superlattices have been investigated for strain relief of the cladding layer, as well as an enhanced hole concentration, which is more than ten times the value obtained for bulk AlGaN films. Laser diodes with strained layer superlattices as cladding layers were shown to have superior structural and electrical properties compared to laser diodes with bulk AlGaN cladding layers. As the period of the strained layer superlattices is decreased, the threshold voltage, as well as the threshold current density, is decreased. The resistance to vertical conduction through p-type superlattices with increasing superlattice period is not offset by the increase in hole concentration for increasing superlattice spacing, resulting in higher voltages.

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3

Weng, Hsu Kai, Akira Nagakubo, Hideyuki Watanabe, and Hirotsugu Ogi. "Lattice thermal conductivity in isotope diamond asymmetric superlattices." Japanese Journal of Applied Physics 61, SG (March 10, 2022): SG1004. http://dx.doi.org/10.35848/1347-4065/ac4304.

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Abstract We study the lattice thermal conductivity of isotope diamond superlattices consisting of 12C and 13C diamond layers at various superlattice periods. It is found that the thermal conductivity of a superlattice is significantly deduced from that of pure diamond because of the reduction of the phonon group velocity near the folded Brillouin zone. The results show that asymmetric superlattices with a different number of layers of 12C and 13C diamonds exhibit higher thermal conductivity than symmetric superlattices even with the same superlattice period, and we find that this can be explained by the trade-off between the effects of phonon specific heat and phonon group velocity. Furthermore, impurities and imperfect superlattice structures are also found to significantly reduce the thermal conductivity, suggesting that these effects can be exploited to control the thermal conductivity over a wide range.

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Antropov, N. О., and Е. А. Kravtsov. "Neutron Reflectometry in Superlattices with Strongly Absorbing Rare-Earth Metals (Gd, Dy)." Поверхность. Рентгеновские, синхротронные и нейтронные исследования, no. 8 (August 1, 2023): 11–15. http://dx.doi.org/10.31857/s1028096023070038.

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Polarized neutron reflectometry was used to study Dy/Gd superlattices with different ratios of Dy and Gd layer thicknesses: 1 : 1, 2 : 1, 3 : 1. It has been experimentally shown that the formation of helical magnetic ordering in Dy layers with a period incommensurate with the period of the superlattice appears as a magnetic superlattice reflection, which is forbidden for structural reasons at a ratio of the thicknesses of the Dy and Gd layers 1 : 1. Otherwise, the formation of helical magnetic ordering has little effect on the shape of the neutron reflectometry curves. Thus, the optimization of the structure of rare-earth superlattices for the neutron reflectometry experiment makes it possible to detect helical magnetic ordering in superlattices with a period incommensurate with the structural superlattice ordering.

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Yu, Yixuan, Avni Jain, Adrien Guillaussier, Vikas Reddy Voggu, Thomas M. Truskett, Detlef-M. Smilgies, and Brian A. Korgel. "Nanocrystal superlattices that exhibit improved order on heating: an example of inverse melting?" Faraday Discussions 181 (2015): 181–92. http://dx.doi.org/10.1039/c5fd00006h.

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Grazing incidence small angle X-ray scattering (GISAXS) measurements reveal that superlattices of 1.7 nm diameter, gold (Au) nanocrystals capped with octadecanethiol become significantly more ordered when heated to moderate temperatures (50–60 °C). This enhancement in order is reversible and the superlattice returns to its initially disordered structure when cooled back to room temperature. Disorder–order transition temperatures were estimated from the GISAXS data using the Hansen–Verlet criterion. Differential scanning calorimetry (DSC) measurements of the superlattices exhibited exotherms (associated with disordering during cooling) and endotherms (associated with ordering during heating) near the transition temperatures. The superlattice transition temperatures also correspond approximately to the melting and solidification points of octadecanethiol. Therefore, it appears that a change in capping ligand packing that occurs upon ligand melting underlies the structural transition of the superlattices. We liken the heat-induced ordering of the superlattices to an inverse melting transition.

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Kabalan, Amal A., and Pritpal Singh. "CdTe/PbTe Superlattice Modeling and Fabrication for Solar Cells Applications." Journal of Nano Research 48 (July 2017): 125–37. http://dx.doi.org/10.4028/www.scientific.net/jnanor.48.125.

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Tuning the bandgap of superlattice structures creates devices with unique optical, electronic and mechanical properties. Designing solar cells with superlattice structures increases the range of light energy absorbed from the solar spectrum in the device. A superlattice is a nanostructure composed of alternating thin layers of two materials. The thickness of the constituent materials alters the optical bandgap of the superlattice. This paper discusses a mathematical model which computes the effective bandgap of a CdTe/PbTe superlattice based on a given thickness of the CdTe and PbTe films. The output of this model is verified by fabricating superlattices with different thickness and measuring their effective bandgaps. The electrochemical atomic layer deposition method is used to fabricate the superlattice structures. The advantage of this method over other vacuum techniques is that it is inexpensive and operates at room temperature. This paper also discusses a method to mitigate the lattice mismatch between the substrate and the superlattice. The optical bandgaps, crystallinity, grain size and chemical composition of the structures are measured using a spectrometer, diffractometer, transmission electron microscope and scanning electron microscope, respectively. The bandgaps of the fabricated superlattices were in agreement with the simulated values. This model can be used for designing the bandgaps of superlattices which can be incorporated in solar cells.

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7

Islam, Md Tanvirul, Xinkang Chen, Tedi Kujofsa, and John E. Ayers. "Chirped Superlattices as Adjustable Strain Platforms for Metamorphic Semiconductor Devices." International Journal of High Speed Electronics and Systems 27, no. 01n02 (March 2018): 1840009. http://dx.doi.org/10.1142/s0129156418400098.

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Chirped superlattices are of interest as buffer layers in metamorphic semiconductor device structures, because they can combine the mismatch accommodating properties of compositionally-graded layers with the dislocation filtering properties of superlattices. Important practical aspects of the chirped superlattice as a buffer layer are the surface strain and surface in-plane lattice constant. In this work two basic types of InGaAs/GaAs chirped superlattice buffers have been studied. In design I (composition modulated), the average composition is varied by modulating the composition of one of the two layers in the superlattice period, but the individual layer thicknesses were fixed. In design II (thickness modulated), the individual layer thicknesses were modulated, but the compositions were fixed. In this paper the surface strain and surface in-plane lattice constant for these chirped superlattices are presented as functions of the top composition and period for each of these basic designs.

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8

Zhao, Lu, Lijuan Zhang, Houfu Song, Hongda Du, Junqiao Wu, Feiyu Kang, and Bo Sun. "Incoherent phonon transport dominates heat conduction across van der Waals superlattices." Applied Physics Letters 121, no. 2 (July 11, 2022): 022201. http://dx.doi.org/10.1063/5.0096861.

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Heat conduction mechanisms in superlattices could be different across different types of interfaces. Van der Waals superlattices are structures physically assembled through weak van der Waals interactions by design and may host properties beyond the traditional superlattices limited by lattice matching and processing compatibility, offering a different type of interface. In this work, natural van der Waals (SnS)1.17(NbS2)n superlattices are synthesized, and their thermal conductivities are measured by time-domain thermoreflectance as a function of interface density. Our results show that heat conduction of (SnS)1.17(NbS2)n superlattices is dominated by interface scattering when the coherent length of phonons is larger than the superlattice period, indicating that incoherent phonon transport dominates through-plane heat conduction in van der Waals superlattices even when the period is atomically thin and abrupt, in contrast to conventional superlattices. Our findings provide valuable insights into the understanding of the thermal behavior of van der Waals superlattices and devise approaches for effective thermal management of superlattices depending on the distinct types of interfaces.

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9

Kim, Jin O., Jan D. Achenbach, Meenam Shinn, and Scott A. Barnett. "Effective Elastic Constants of Superlattice Films Measured by Line-Focus Acoustic Microscopy." Journal of Engineering Materials and Technology 117, no. 4 (October 1, 1995): 395–401. http://dx.doi.org/10.1115/1.2804732.

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The effective elastic constants of single-crystal nitride superlattice films have been determined by calculation and by measurement methods. The calculation method uses formulas to calculate the effective elastic constants of superlattices from the measured elastic constants of the constituent layers. The calculated effective elastic constants are tested by comparing the corresponding surface acoustic wave (SAW) velocities calculated for thin-film/substrate systems with the corresponding SAW velocities measured by line-focus acoustic microscopy (LFAM). The measurement method determines the effective elastic constants of the superlattices directly from the SAW velocity dispersion data measured by LFAM. Two kinds of superlattice films are considered: one has relatively flat and sharp interfaces between layers, and the other has rough interfaces with interdiffusion. The calculation method has yielded very good results for the superlattices with flat and sharp interfaces but not for the superlattices with rough interfaces. The measurement method yields results for both kinds, with the restriction that the constituent layers have similar crystal symmetries.

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10

Sidorkin, Alexander, Lolita Nesterenko, Yaovi Gagou, Pierre Saint-Gregoire, Eugeniy Vorotnikov, and Nadezhda Popravko. "Dielectric Properties and Switching Processes of Barium Titanate–Barium Zirconate Ferroelectric Superlattices." Materials 11, no. 8 (August 14, 2018): 1436. http://dx.doi.org/10.3390/ma11081436.

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This article is devoted to the investigation of the dielectric and repolarization properties of barium zirconate and barium titanate BaZrO3/BaTiO3 superlattices with a period of 13.322 nm on a monocrystal magnesium oxide (MgO) substrate. Synthesized superlattices demonstrated a ferroelectric phase transition at a temperature of approximately 393 °C, which is far higher than the Curie temperature of BaTiO3 thin films and bulk samples. The dielectric permittivity of the superlattice reached more than 104 at maximum. As the electric field frequency increased, the dielectric constant of the studied superlattice decreased over the entire study temperature range, but position of the maximum dielectric constant remained the same with changing frequency. The temperature dependence of the inverse dielectric permittivity 1/ε(T) for the studied samples shows that, in the investigated superlattice, both Curie–Weiss law and the law of “two” were followed. Additionally, the ε(T) dependences showed practically no temperature hysteresis with heating and cooling. Samples of synthesized superlattices had a relatively small internal bias field, which was directed from the superlattice towards the substrate.

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11

Zhang, Wei-Chao, Hao Wu, Wei-Feng Sun, and Zhen-Peng Zhang. "First-Principles Study of n*AlN/n*ScN Superlattices with High Dielectric Capacity for Energy Storage." Nanomaterials 12, no. 12 (June 8, 2022): 1966. http://dx.doi.org/10.3390/nano12121966.

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As a paradigm of exploiting electronic-structure engineering on semiconductor superlattices to develop advanced dielectric film materials with high electrical energy storage, the n*AlN/n*ScN superlattices are systematically investigated by first-principles calculations of structural stability, band structure and dielectric polarizability. Electrical energy storage density is evaluated by dielectric permittivity under a high electric field approaching the uppermost critical value determined by a superlattice band gap, which hinges on the constituent layer thickness and crystallographic orientation of superlattices. It is demonstrated that the constituent layer thickness as indicated by larger n and superlattice orientations as in (111) crystallographic plane can be effectively exploited to modify dielectric permittivity and band gap, respectively, and thus promote energy density of electric capacitors. Simultaneously increasing the thicknesses of individual constituent layers maintains adequate band gaps while slightly reducing dielectric polarizability from electronic localization of valence band-edge in ScN constituent layers. The AlN/ScN superlattices oriented in the wurtzite (111) plane acquire higher dielectric energy density due to the significant improvement in electronic band gaps. The present study renders a framework for modifying the band gap and dielectric properties to acquire high energy storage in semiconductor superlattices.

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12

Webb, Matthew, Tao Ma, Allen H. Hunter, Sean McSherry, Jonathan Kaufman, Zihao Deng, William B. Carter, et al. "Geometric defects induced by strain relaxation in thin film oxide superlattices." Journal of Applied Physics 132, no. 18 (November 14, 2022): 185307. http://dx.doi.org/10.1063/5.0120176.

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Functional thin film superlattices with stability in extreme environments can lead to transformative performance in optical and thermal applications such as thermophotovoltaics. In this work, key issues associated with defects that prevent layer-by-layer growth in epitaxial, low-miscibility oxide superlattices are investigated. Layer protrusions, approximately 8 nm wide and 3 nm thick, arise from a strain relaxation mechanism in 8 nm bilayer superlattices of Ba(Zr0.5Hf0.5)O3/MgO and propagate through the subsequent superlattice layers forming an inverted pyramid structure that is spatially phase offset from the matrix. The density and size of these defects scales with the number of interfaces in the sample, indicating that surface roughness during growth is a significant factor in the formation of these defects. In situ high temperature transmission electron microscopy (1000 °C, in vacuo) measurement reveals that phase decomposition of Ba(Zr0.5Hf0.5)O3 and decoherence of the superlattice is nucleated by these defects. This work highlights that achieving optimum growth conditions is imperative to the synthesis of single-crystalline superlattices with sharp interfaces for optimized performance in extreme environments.

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13

Gu, X. Wendy, Xingchen Ye, David M. Koshy, Shraddha Vachhani, Peter Hosemann, and A. Paul Alivisatos. "Tolerance to structural disorder and tunable mechanical behavior in self-assembled superlattices of polymer-grafted nanocrystals." Proceedings of the National Academy of Sciences 114, no. 11 (February 27, 2017): 2836–41. http://dx.doi.org/10.1073/pnas.1618508114.

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Large, freestanding membranes with remarkably high elastic modulus (>10 GPa) have been fabricated through the self-assembly of ligand-stabilized inorganic nanocrystals, even though these nanocrystals are connected only by soft organic ligands (e.g., dodecanethiol or DNA) that are not cross-linked or entangled. Recent developments in the synthesis of polymer-grafted nanocrystals have greatly expanded the library of accessible superlattice architectures, which allows superlattice mechanical behavior to be linked to specific structural features. Here, colloidal self-assembly is used to organize polystyrene-grafted Au nanocrystals at a fluid interface to form ordered solids with sub-10-nm periodic features. Thin-film buckling and nanoindentation are used to evaluate the mechanical behavior of polymer-grafted nanocrystal superlattices while exploring the role of polymer structural conformation, nanocrystal packing, and superlattice dimensions. Superlattices containing 3–20 vol % Au are found to have an elastic modulus of ∼6–19 GPa, and hardness of ∼120–170 MPa. We find that rapidly self-assembled superlattices have the highest elastic modulus, despite containing significant structural defects. Polymer extension, interdigitation, and grafting density are determined to be critical parameters that govern superlattice elastic and plastic deformation.

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Kudasov, Yu B., and Dmitry Andreevich Maslov. "Magnetic Structure of Fe/V Superlattices with Variable Thickness of Iron Layers." Solid State Phenomena 152-153 (April 2009): 209–12. http://dx.doi.org/10.4028/www.scientific.net/ssp.152-153.209.

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The model of magnetic structure of Fe/V superlattices is discussed. An individual iron layer of 2 or 3 ML in thickness is assumed to be a XY system. An interlayer interaction through vanadium spacers leads to the appearing of effective field for each iron layer. The infinite and finite superlattices are investigated. Calculations of magnetic structure of Fe2/V12/Fe3/V12 superlattice show that divergence in estimations of the critical temperature obtained by neutron scattering and MOKE is due to inhomogeneity of magnetic moment distribution in the finite superlattice.

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W. Tian, J. C. Jiang, X. Q. Pan, C.D. Theis, and D.G. Schlom. "Microstructure of PbTi03/SrTi03 Superlattice Grown by MBE." Microscopy and Microanalysis 4, S2 (July 1998): 576–77. http://dx.doi.org/10.1017/s143192760002300x.

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Ferroelectric superlattices have been actively and intensively studied in recent years for their great scientific and technological interest. Superlattice containing Pb-based ferroelectric layers are important among ferroelectric superlattice systems, however, it is difficult to grow such superlattice due to the high volatility of Pb. Recently, great progress has been made in fabricating superlattice structure of PbZrO3/PbTiO3 by multi-ion-beam sputtering’ and molecular beam epitaxy (MBE). In this paper, we report the microstructural investigations of PbTiO3/SrTiO3 superlattice films, which were epitaxially grown on the SrTi03 substrate by MBE, using transmission electron microscopy (TEM).[(PbTiO3)l0/(SrTiO3)l0]15 superlattice films were stacked on (100) SrTiO3 substrate alternately by MBE. Before growing the superlattice structure, a baffle layer including the 1000Å La-doped SrTi03 and the subsequent 500 Å PbTiO3 thin films was grown on the substrate. Above the PbTi03/SrTi03 superlattices, another PbTi03 thin film (1000 Å) was grown. Cross-section TEM specimens were prepared by standard methods.

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Staszczak, Grzegorz, Iza Gorczyca, Ewa Grzanka, Julita Smalc-Koziorowska, Grzegorz Targowski, and Tadeusz Suski. "Toward Red Light Emitters Based on InGaN-Containing Short-Period Superlattices with InGaN Buffers." Materials 16, no. 23 (November 27, 2023): 7386. http://dx.doi.org/10.3390/ma16237386.

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In order to shift the light emission of nitride quantum structures towards the red color, the technological problem of low In incorporation in InGaN−based heterostructures has to be solved. To overcome this problem, we consider superlattices grown on InGaN buffers with different In content. Based on the comparison of the calculated ab initio superlattice band gaps with the photoluminescence emission energies obtained from the measurements on the specially designed samples grown by metal-organic vapor phase epitaxy, it is shown that by changing the superlattice parameters and the composition of the buffer structures, the light emission can be shifted to lower energies by about 167 nm (0.72 eV) in comparison to the case of a similar type of superlattices grown on GaN substrate. The importance of using superlattices to achieve red emission and the critical role of the InGaN buffer are demonstrated.

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17

XU, MING, WENXUE YU, GUANGMING LUO, CHUNLING CHAI, TONG ZHAO, FAN CHEN, ZHENHONG MAI, WUYAN LAI, ZHONGHUA WU, and DEWU WANG. "ON THE CHARACTERIZATION OF METALLIC SUPERLATTICE STRUCTURES BY X-RAY DIFFRACTION." Modern Physics Letters B 13, no. 19 (August 20, 1999): 663–69. http://dx.doi.org/10.1142/s021798499900083x.

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To solve the problem on the microstructural characterization of metallic superlattices, taking the NiFe/Cu superlattices as example, we show that the structures of metallic superlattices can be characterized exactly by combining low-angle X-ray diffraction with high-angle X-ray diffraction. First, we determine exactly the total film thickness by a straightforward and precise method based on a modified Bragg law from the subsidiary maxima around the low-angle X-ray diffraction peak. Then, by combining with the simulation of high-angle X-ray diffraction, we obtain the structural parameters such as the superlattice period, the sublayer and buffer thickness. This characterization procedure is also applicable to other types of metallic superlattices.

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Yonezawa, Yu, Hiroyuki Kinbara, Hiroki Umehara, Hirofumi Kakemoto, Takuya Hoshina, Hiroaki Takeda, and Takaaki Tsurumi. "Fabrication of Dielectric/Conductive Hybrid Artificial Superlattices Using Molecular Beam Epitaxy Method." Key Engineering Materials 421-422 (December 2009): 139–42. http://dx.doi.org/10.4028/www.scientific.net/kem.421-422.139.

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Artificial super-lattices of [(BaTiO3)/(SrTiO3)10]4 (BTO10/STO10) were fabricated on STO(001) substrate by the molecular beam epitaxy method (MBE), and the molecular layers of SrRuO3(SRO) was introduced into these superlattices as conductive layers. The superlattices introduced two conductive layers showed the enormous dielectric permittivity. On the other hand, the permittivity of the superlattice introduced one conductive layer was almost same as that of BTO10/STO10. In the case of introducing two conductive layers, the moving electrons between two layers induced the interfacial polarization. Especially, the superlattice with two SRO conductive layers, the distance between these layers in a superlattice is 18 molecular layers, showed the highest relaxation frequency 132 kHz and biggest capacitance.

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19

Hoglund, Eric R., De-Liang Bao, Andrew O’Hara, Sara Makarem, Zachary T. Piontkowski, Joseph R. Matson, Ajay K. Yadav, et al. "Emergent interface vibrational structure of oxide superlattices." Nature 601, no. 7894 (January 26, 2022): 556–61. http://dx.doi.org/10.1038/s41586-021-04238-z.

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AbstractAs the length scales of materials decrease, the heterogeneities associated with interfaces become almost as important as the surrounding materials. This has led to extensive studies of emergent electronic and magnetic interface properties in superlattices1–9. However, the interfacial vibrations that affect the phonon-mediated properties, such as thermal conductivity10,11, are measured using macroscopic techniques that lack spatial resolution. Although it is accepted that intrinsic phonons change near boundaries12,13, the physical mechanisms and length scales through which interfacial effects influence materials remain unclear. Here we demonstrate the localized vibrational response of interfaces in strontium titanate–calcium titanate superlattices by combining advanced scanning transmission electron microscopy imaging and spectroscopy, density functional theory calculations and ultrafast optical spectroscopy. Structurally diffuse interfaces that bridge the bounding materials are observed and this local structure creates phonon modes that determine the global response of the superlattice once the spacing of the interfaces approaches the phonon spatial extent. Our results provide direct visualization of the progression of the local atomic structure and interface vibrations as they come to determine the vibrational response of an entire superlattice. Direct observation of such local atomic and vibrational phenomena demonstrates that their spatial extent needs to be quantified to understand macroscopic behaviour. Tailoring interfaces, and knowing their local vibrational response, provides a means of pursuing designer solids with emergent infrared and thermal responses.

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Twigg, M. E., B. R. Bennett, J. R. Waterman, J. L. Davis, B. V. Shanabrook, and R. J. Wagner. "Interfacial properties of GaSb/InAs superlattices." Proceedings, annual meeting, Electron Microscopy Society of America 51 (August 1, 1993): 826–27. http://dx.doi.org/10.1017/s0424820100149969.

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Recently, the GaSb/InAs superlattice system has received renewed attention. The interest stems from a model demonstrating that short period Ga1-xInxSb/InAs superlattices will have both a band gap less than 100 meV and high optical absorption coefficients, principal requirements for infrared detector applications. Because this superlattice system contains two species of cations and anions, it is possible to prepare either InSb-like or GaAs-like interfaces. As such, the system presents a unique opportunity to examine interfacial properties.We used molecular beam epitaxy (MBE) to prepare an extensive set of GaSb/InAs superlattices grown on an GaSb buffer, which, in turn had been grown on a (100) GaAs substrate. Through appropriate shutter sequences, the interfaces were directed to assume either an InSb-like or GaAs-like character. These superlattices were then studied with a variety of ex-situ probes such as x-ray diffraction and Raman spectroscopy. These probes confirmed that, indeed, predominantly InSb-like and GaAs-like interfaces had been achieved.

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Sankin, Vladimir Ilich, Alexey G. Petrov, Pavel P. Shkrebiy, Olga P. Kazarova, and Alexander A. Lebedev. "SiC Natural and Artificial Superlattices for the Implementation of the Bloch Oscillation Process: A Comparative Analysis." Materials Science Forum 1004 (July 2020): 256–64. http://dx.doi.org/10.4028/www.scientific.net/msf.1004.256.

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Bloch oscillations in semiconductors have been studied for several decades. Oscillations were observed in artificial superlattices based on AlGaAs-GaAs proposed Esaki and Tsu, and the natural superlattice based on superstructures SiC. In this paper we considers some base properties of the SiC natural superlattices that are the ground for the Bloch oscillations existence in these materials and attract attention to the some main disadvantages of the artificial superlattices. The experimental detection of the Bloch oscillation-dependent physical effects in semiconductors has been an actual problem over decades.

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Ren, Shang-Fen, and Jason Stanfield. "Interface Phonon Modes in Strained Semiconductor Superlattices." International Journal of Modern Physics B 12, no. 29n31 (December 20, 1998): 3137–40. http://dx.doi.org/10.1142/s0217979298002222.

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Phonon modes in strained ZnTe/CdSe superlattices are studied. The macroscopic interface modes and two different types of microscopic interface modes are identified. Interface phonon modes in (ZnTe)8(CdSe)8 superlattice with interchange of atomic layers across interfaces are calculated and compared with the results of superlattice with ideal interfaces.

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WILSON, K. S. JOSEPH, and K. NAVANEETHAKRISHNAN. "PHONON POLARITON MODES IN QUANTUM DOT SUPERLATTICES." Modern Physics Letters B 18, no. 02n03 (February 10, 2004): 105–12. http://dx.doi.org/10.1142/s021798490400672x.

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The phonon polariton modes in a quantum dot superlattice system are calculated, extending an earlier theory developed for quantum well and quantum well wire superlattices.14 Results are presented for the GaAs/GaP superlattice system as an example. Our findings exihibit the bulk polariton and the quantum well behaviors as limiting cases.

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Eymery, J. "Localized destructive interference in X-ray specular reflectivity." Journal of Applied Crystallography 32, no. 5 (October 1, 1999): 859–63. http://dx.doi.org/10.1107/s0021889899006238.

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Localized destructive interference can be obtained for specific values of the angle of incidence when studying semiconductor superlattices with X-ray reflectivity at fixed wavelength. Kinematical calculations show that the difference between the real parts of the refractive index of the layers must be small, and that the number of superlattice periods must be optimized to enhance the destructive interference. An experimental example, involving a CdTe/CdZnTe superlattice, and optical matrix simulations for SiGe/Si superlattices are presented to illustrate this effect. Finally, it is shown that such structures can be tailored to act as energy filters at fixed angles of incidence.

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Wang, Bruce, Antonio Bianconi, Ian D. R. Mackinnon, and Jose A. Alarco. "Superlattice Delineated Fermi Surface Nesting and Electron-Phonon Coupling in CaC6." Crystals 14, no. 6 (May 24, 2024): 499. http://dx.doi.org/10.3390/cryst14060499.

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The superconductivity of CaC6 as a function of pressure and Ca isotopic composition was revisited using DFT calculations on a 2c–double hexagonal superlattice. The introduction of superlattices was motivated by previous synchrotron absorption and Raman spectroscopy results on other superconductors that showed evidence of superlattice vibrations at low (THz) frequencies. For CaC6, superlattices have previously been invoked to explain the ARPES data. A superlattice along the hexagonal c-axis direction is also illustrative of atomic orbital symmetry and periodicity, including bonding and antibonding s-orbital character implied by cosine-modulated electronic bands. Inspection of the cosine band revealed that the cosine function has a small (meV) energy difference between the bonding and antibonding regions, relative to a midpoint non-bonding energy. Fermi surface nesting was apparent in an appropriately folded Fermi surface using a superlattice construct. Nesting relationships identified phonon vectors for the conservation of energy and for phase coherency between coupled electrons at opposite sides of the Fermi surface. A detailed analysis of this Fermi surface nesting provided accurate estimates of the superconducting gaps for CaC6 with the change in applied pressure. The recognition of superlattices within a rhombohedral or hexagonal representation provides consistent mechanistic insight on superconductivity and electron−phonon coupling in CaC6.

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Sanina, Viktoriya, Boris Khannanov, and Evgenii Golovenchits. "Optical Control of Superlattices States Formed Due to Electronic Phase Separation in Multiferroic Eu0.8Ce0.2Mn2O5." Nanomaterials 11, no. 7 (June 24, 2021): 1664. http://dx.doi.org/10.3390/nano11071664.

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The effect of optical pumping and magnetic field on properties of the electronic phase separation regions, which are the multiferroic semiconductor heterostructures in the form of superlattices, have been studied in Eu0.8Ce0.2Mn2O5. These superlattices are formed due to self-organization in a dielectric crystal matrix as a result of the competing internal interactions balance and occupy a small crystal volume. The dynamical equilibrium states of superlattices are initially formed during cycling of as-grown samples in a magnetic field. The superlattices in such states are ferromagnetic and electrically neutral. Sets of ferromagnetic resonances were observed from individual layers of superlattices. Their features give rise information on properties of these layers and of a superlattice as a whole. The differences in the parameters of these resonances were due to different distributions of Mn3+ and Mn4+ ions in individual superlattices layers. It has been found that optical pumping having different powers allows us to control of multiferroic properties of superlattices layers by changing their magnetic and electric properties. It is shown that, under certain conditions, it is possible to significantly increase the temperatures at which multiferroic heterostructures exist.

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Jaszczak, J. A., and D. Wolf. "On the elastic behavior of composition-modulated superlattices." Journal of Materials Research 6, no. 6 (June 1991): 1207–18. http://dx.doi.org/10.1557/jmr.1991.1207.

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Atomistic computer simulations are used to systematically investigate the role of interfacial disorder on the elastic behavior of composition-modulated superlattices of fcc metals, represented by simple Lennard–Jones potentials. The structures, energies, and average elastic properties of four types of superlattices with various degrees of interfacial disorder are computed as a function of the modulation wavelength along [001]. The four superlattice types studied include perfectly coherent, incoherent, and two types derived from these by introducing relative twists about [001] between alternating layers. A 20% lattice-parameter mismatch between the two modulating materials is assumed. Results are compared with our earlier work on unsupported thin films, grain-boundary superlattices, and incoherent superlattices with a 10% lattice-parameter mismatch. The degree of structural disorder at the interfaces is found to correlate well with the magnitude of the elastic anomalies, which cannot be accounted for by anisotropic lattice-parameter changes alone. The grain-boundary superlattices studied earlier are found to provide a good model limit for the elastic behavior of interfacially disordered dissimilar-material superlattices.

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Park, K., L. Salamanca-Riba, and B. T. Jonker. "TEM studies of (ZnSe/FeSe) superlattices." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 2 (August 1992): 1382–83. http://dx.doi.org/10.1017/s0424820100131541.

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Diluted magnetic semiconductors (DMS) are of considerable interest in the area of heterostructures and superlattices because the lattice parameter, energy gap, and effective mass can be “tuned” in a controlled fashion by varying the composition. This tunability has been exploited in the fabrication of DMS superlattices. Since the superlattices can be grown with a wide range of choices of materials, there is a great variety of possible applications requiring magneto-optical properties. However, the lattice mismatch between the constituent layers in the superlattice and between the superlattice and the substrate makes it difficult to grow high quality superlattices.Superlattices of (11.4 Å FeSe/34.0 Å ZnSe)12 (sample A) and (20.0 Å FeSe/45.3 Å ZnSe)6 (sample B) were grown on (001) GaAs substrates using MBE. Sample A was grown on a ZnSe buffer layer with a thickness of 500 Å on a (001) GaAs substrate, while sample B was grown directly on a GaAs substrate. TEM samples were prepared by mechanical grinding, dimple grinding, and ion-milling (3.0 keV Ar+ ions and 1 mA current) at liquid nitrogen temperature.

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Saito, Yuta, Paul Fons, Kirill V. Mitrofanov, Kotaro Makino, Junji Tominaga, John Robertson, and Alexander V. Kolobov. "Chalcogenide van der Waals superlattices: a case example of interfacial phase-change memory." Pure and Applied Chemistry 91, no. 11 (November 26, 2019): 1777–86. http://dx.doi.org/10.1515/pac-2019-0105.

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Abstract 2D van der Waals chalcogenides such as topological insulators and transition-metal dichalcogenides and their heterostructures are now at the forefront of semiconductor research. In this paper, we discuss the fundamental features and advantages of van der Waals bonded superlattices over conventional superlattices made of 3D materials and describe in more detail one practical example, namely, interfacial phase change memory based on GeTe–Sb2Te3 superlattice structures.

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John, J. D., S. Nishimoto, N. Kadowaki, I. Saito, K. Okano, S. Okano, D. R. T. Zahn, et al. "Quantum device designing (QDD) for future semiconductor engineering." Review of Scientific Instruments 93, no. 3 (March 1, 2022): 034703. http://dx.doi.org/10.1063/5.0081544.

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In semiconductor device history, a trend is observed where narrowing and increasing the number of material layers improve device functionality, with diodes, transistors, thyristors, and superlattices following this trend. While superlattices promise unique functionality, they are not widely adopted due to a technology barrier, requiring advanced fabrication, such as molecular beam epitaxy and lattice-matched materials. Here, a method to design quantum devices using amorphous materials and physical vapor deposition is presented. It is shown that the multiplication gain M depends on the number of layers of the superlattice, N, as M = kN, with k as a factor indicating the efficiency of multiplication. This M is, however, a trade-off with transit time, which also depends on N. To demonstrate, photodetector devices are fabricated on Si, with the superlattice of Se and As2Se3, and characterized using current–voltage ( I– V) and current–time ( I– T) measurements. For superlattices with the total layer thicknesses of 200 nm and 2 μm, the results show that k200nm = 0.916 and k2 μm = 0.384, respectively. The results confirm that the multiplication factor is related to the number of superlattice layers, showing the effectiveness of the design approach.

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Goepfert, I. D., E. F. Schubert, A. Osinsky, and P. E. Norris. "Efficient Acceptor Activation in AlxGa1−xN/GaN Doped Superlattices." MRS Internet Journal of Nitride Semiconductor Research 5, S1 (2000): 329–35. http://dx.doi.org/10.1557/s1092578300004464.

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Mg-doped superlattices consisting of uniformly doped AlxGa1−xN and GaN layers are analyzed by Hall-effect measurements. Acceptor activation energies of 70 meV and 58 meV are obtained for superlattice structures with an Al mole fraction of x = 0.10 and 0.20 in the barrier layers, respectively. These energies are significantly lower than the activation energy measured for Mg-doped GaN thin films. At room temperature, the doped superlattices have free hole concentrations of 2 × 1018 cm−3 and 4 × 1018 cm−3 for x = 0.10 and 0.20, respectively. The increase in hole concentration with Al content of the superlattice is consistent with theory. The room temperature conductivity measured for the superlattice structures are 0.27 S/cm and 0.64 S/cm for an Al mole fraction of x = 0.10 and 0.20, respectively.

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32

Harfenist, S. A., Z. L. Wang, R. L. Whetten, I. Vezmar, M. M. Alvarez, and B. E. Salisbury. "Three-Dimensional Hexagonal Close-Packed Superlattices of Passivated Ag Nanocrystals." Microscopy and Microanalysis 3, S2 (August 1997): 431–32. http://dx.doi.org/10.1017/s1431927600009041.

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Silver nanocrystals passivated by dodecanethiol self-assembled monolayers were produced using an aerosol technique described in detail elsewhere [1]. Self-assembling passivated nanocrystal-superlattices (NCS's) involve self-organization into monolayers, thin films, and superlattices of size-selected nanoclusters encapsulated in a protective compact coating [2,3,4,5,6,7]. We report the preparation and structure characterization of three-dimensional (3-D) hexagonal close-packed Ag nanocrystal supercrystals from Ag nanocrystals of ˜4.5 nm in diameters. The crystallography of the superlattice and atomic core lattices were determined using transmission electron microscopy (TEM) and high-resolution TEM.SEM was used to image the nanocrystal superlattices formed on an amorphous carbon film of an TEM specimen grid (fig. la). The superlattice films show well shaped, sharply faceted, triangular shaped sheets. Figure lb depicts numerous Ag nanocrystal aggregates uniformly distributed over the imaging region. Inset in this figure is an enlargement of the boxed region at the edge of a supercrystal typifying the ordered nanocrystal packing.

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Panomsuwan, Gasidit, Nagahiro Saito, and Osamu Takai. "Structural Properties and Microstructures of SrTiO₃/SrTi_1-xNb_xO₃ Superlattices Grown by Ion Beam Deposition." Materials Science Forum 695 (July 2011): 598–601. http://dx.doi.org/10.4028/www.scientific.net/msf.695.598.

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Superlattice structure of SrTiO3and Nb-doped SrTiO3have been epitaxially grown on atomically flat surface of LaAlO3substrates by ion beam deposition method. Epitaxial superlattices were grown at 800 °C in the presence of partial oxygen pressure under optimizing growth conditions. The Nb-doped SrTiO3layers were varied from 2 to 15 unit cell thickness approximately, while SrTiO3layers are maintained at 15 unit cell thickness with 10 periods. The superlattices with various Nb-doped SrTiO3layer thicknesses were investigated using X-ray diffractometer (XRD) and atomic force microscope (AFM), in order to clearly understand structural properties and surface structure, which are significant for fabrication of the high quality superlattice structure.

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Högberg, H., J. Birch, M. Odén, J.-O. Malm, L. Hultman, and U. Jansson. "Growth, structure, and mechanical properties of transition metal carbide superlattices." Journal of Materials Research 16, no. 5 (May 2001): 1301–10. http://dx.doi.org/10.1557/jmr.2001.0182.

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Superlattices of TiC/VC have been deposited on MgO(001) substrates by simultaneous direct current metal magnetron sputtering and C60 evaporation in the temperature range 200–800 °C. Thin superlattices (approximately 1000 Å) deposited at 400 °C exhibited an epitaxial growth with abrupt interfaces while films deposited at 200 °C showed a partial loss of epitaxy. At 800 °C roughening by surface diffusion started to degrade the superlattices and introduced a columnar microstructure. A loss of epitaxy was observed for thicker (>7000 Å) superlattice films deposited at 400 °C. The results suggest that this observation is due to difficulties in depositing epitaxial VC.

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Jin, Cai, Wanrong Geng, Linjing Wang, Wenqiao Han, Dongfeng Zheng, Songbai Hu, Mao Ye, et al. "Tuning ferroelectricity and ferromagnetism in BiFeO3/BiMnO3 superlattices." Nanoscale 12, no. 17 (2020): 9810–16. http://dx.doi.org/10.1039/c9nr09670a.

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Superlattice structure provides an effective path for integrating multifunctional properties. The interfacial coupling in the ferromagnetic/ferroelectric superlattices is a possible route to achieve multiferroicity.

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36

Yun, Hongseok, and Taejong Paik. "Colloidal Self-Assembly of Inorganic Nanocrystals into Superlattice Thin-Films and Multiscale Nanostructures." Nanomaterials 9, no. 9 (September 1, 2019): 1243. http://dx.doi.org/10.3390/nano9091243.

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The self-assembly of colloidal inorganic nanocrystals (NCs) offers tremendous potential for the design of solution-processed multi-functional inorganic thin-films or nanostructures. To date, the self-assembly of various inorganic NCs, such as plasmonic metal, metal oxide, quantum dots, magnetics, and dielectrics, are reported to form single, binary, and even ternary superlattices with long-range orientational and positional order over a large area. In addition, the controlled coupling between NC building blocks in the highly ordered superlattices gives rise to novel collective properties, providing unique optical, magnetic, electronic, and catalytic properties. In this review, we introduce the self-assembly of inorganic NCs and the experimental process to form single and multicomponent superlattices, and we also describe the fabrication of multiscale NC superlattices with anisotropic NC building blocks, thin-film patterning, and the supracrystal formation of superlattice structures.

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37

KILLI, MATTHEW, SI WU, and ARUN PARAMEKANTI. "GRAPHENE: KINKS, SUPERLATTICES, LANDAU LEVELS AND MAGNETOTRANSPORT." International Journal of Modern Physics B 26, no. 21 (July 18, 2012): 1242007. http://dx.doi.org/10.1142/s0217979212420076.

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We review recent work on superlattices in monolayer and bilayer graphene. We highlight the role of the quasiparticle chirality in generating new Dirac fermion modes with tunable anisotropic velocities in one dimensional (1D) superlattices in both monolayer and bilayer graphene. We discuss the structure of the Landau levels and magnetotransport in such superlattices over a wide range of perpendicular (orbital) magnetic fields. In monolayer graphene, we show that an orbital magnetic field can reverse the anisotropy of the transport imposed by the superlattice potential, suggesting possible switching-type device applications. We also consider topological modes localized at a kink in an electric field applied perpendicular to bilayer graphene, and show how interactions convert these modes into a two-band Luttinger liquid with tunable Luttinger parameters. The band structures of electric field superlattices in bilayer graphene (with or without a magnetic field) are shown to arise naturally from a coupled array of such topological modes. We briefly review some bandstructure results for 2D superlattices. We conclude with a discussion of recent tunneling and transport experiments and point out open issues.

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Li, Xiaowen, Xiaobin Qiang, Zhenhao Gong, Yubo Zhang, Penglai Gong, and Lang Chen. "Tunable Negative Poisson’s Ratio in Van der Waals Superlattice." Research 2021 (April 10, 2021): 1–11. http://dx.doi.org/10.34133/2021/1904839.

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Negative Poisson’s ratio (NPR) materials are functional and mechanical metamaterials that shrink (expand) longitudinally after being compressed (stretched) laterally. By using first-principles calculations, we found that Poisson’s ratio can be tuned from near zero to negative by different stacking modes in van der Waals (vdW) graphene/hexagonal boron nitride (G/h-BN) superlattice. We attribute the NPR effect to the interaction of pz orbitals between the interfacial layers. Furthermore, a parameter calculated by analyzing the electronic band structure, namely, distance-dependent hopping integral, is used to describe the intensity of this interaction. We believe that this mechanism is not only applicable to G/h-BN superlattice but can also explain and predict the NPR effect in other vdW layered superlattices. Therefore, the NPR phenomenon, which was relatively rare in 3D and 2D materials, can be realized in the vdW superlattices by different stacking orders. The combinations of tunable NPRs with the excellent electrical/optical properties of 2D vdW superlattices will pave a novel avenue to a wide range of multifunctional applications.

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39

Hsu, Y., T. S. Kuan, and W. I. Wang. "Effects of substrate orientation on growth of epitaxial layers." Proceedings, annual meeting, Electron Microscopy Society of America 54 (August 11, 1996): 948–49. http://dx.doi.org/10.1017/s0424820100167202.

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Semiconductor superlattices or epitaxial overlayers have so far been grown mostly on (100)-oriented substrates. It has long been suspected that growth on surfaces such as (m11) could produce equally good or better epitaxial layers. In this work, we have systematically tested the growth of multi- or single-layered structures, including the GaAs/AlAs, AlAs/Ge, and GaAs/Si systems, on surfaces of different orientations. The crystallinity and defect mechanisms in the layers grown on (100), (311), and (511) surfaces at different temperatures were compared. In most cases we found that (311) surfaces can produce epitaxial layers as good as on (100) surfaces.Perfect lattice-matched GaAs/AIAs superlattices were grown on (311)A-, (311)B-, and (100)-oriented GaAs substrates. Superlattices with good layer morphology were achieved on all three surfaces at 600°C. Fig. 1(a) shows an image of a typical GaAs/AIAs superlattice grown on a (311)B surface. This superlattice exhibits sharp interface abruptness as indicated by the high-order satellites observed in the diffraction pattern in Fig. 1(b).

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Zhu, Zhen Ye, Jing Bai, Fei Lu, and Qian Wang. "First-Principles Study of Polarization Behavior in BaTiO₃/PbTiO₃ Ferroelectric Superlattices." Advanced Materials Research 833 (November 2013): 3–7. http://dx.doi.org/10.4028/www.scientific.net/amr.833.3.

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We performed the first principle calculation to investigate the polarization behavior of BaTiO3(BTO)/PbTiO3(PTO) superlattices with a period-5 superlattice model. The results show that when BTO proportion increases, values of c/a increase and polarizations decrease. In BPT superlattices, polarization in each local layer keeps a constant value, indicating that short-period BPT superlattices can be approximately considered as a single ferroelectric material. Moreover, from analysis of the electrostatic model, we know the directions of internal electric fields in BTO and PTO layers are opposite. Internal electric field in PTO layer leads to polarization loss in this layer, but polarization in BTO layer is enhanced by internal electric field.

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41

Mancoff, F. B., J. F. Bobo, O. E. Richter, K. Bessho, P. R. Johnson, R. Sinclair, W. D. Nix, R. L. White, and B. M. Clemens. "Growth and Characterization of Epitaxial NiMnSb/PtMnSb C1b Heusler alloy superlattices." Journal of Materials Research 14, no. 4 (April 1999): 1560–69. http://dx.doi.org/10.1557/jmr.1999.0209.

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We have sputter deposited NiMnSb/PtMnSb Heusler alloy superlattices with bilayer periods from 9–160 Å. X-ray diffraction and cross-sectional transmission electron microscopy (TEM) measurements indicate that even for short bilayer periods, the superlattices are compositionally modulated, epitaxial, and maintain the Heusler alloy C1b structure. Low- and high-angle diffraction profiles are in agreement with simulations of the superlattice peaks. TEM images reveal defects, including stacking faults, which help relieve lattice mismatch strain. Energy minimization calculations of the stacking fault density are within a factor of 3 of the density observed by TEM. The saturation magnetization of the superlattices is close to bulk PtMnSb and NiMnSb, with a tendency for perpendicular magnetization at short bilayer periods.

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42

McKinnon, G. H., J. N. McMullin, D. Landheer, M. Buchanan, P. Janega, and M. W. Denhoff. "Selective contacts for silicon-doping superlattices." Canadian Journal of Physics 67, no. 4 (April 1, 1989): 326–29. http://dx.doi.org/10.1139/p89-057.

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Results are presented that show that selective n- and p-type contacts with low resistance have been formed on silicon-doping superlattices. The superlattices were grown by molecular-beam epitaxy through a silicon mask to create built-in blocking regions at the edges of the mesas. Contacts of Mg2Si for the n-side and PtSi for the p-side were formed along the edges of the mesa, resulting in a successful diode-like behavior. A surface etch to remove doping impurities from the region surrounding the superlattice mesa was required to maintain contact–substrate isolation.

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Noguchi, Yuji, and Hiroki Matsuo. "Polarization and Dielectric Properties of BiFeO3-BaTiO3 Superlattice-Structured Ferroelectric Films." Nanomaterials 11, no. 7 (July 19, 2021): 1857. http://dx.doi.org/10.3390/nano11071857.

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Superlattice-structured epitaxial thin films composed of Mn(5%)-doped BiFeO3 and BaTiO3 with a total thickness of 600 perovskite (ABO3) unit cells were grown on single-crystal SrTiO3 substrates by pulsed laser deposition, and their polarization and dielectric properties were investigated. When the layers of Mn-BiFeO3 and BaTiO3 have over 25 ABO3 unit cells (N), the superlattice can be regarded as a simple series connection of their individual capacitors. The superlattices with an N of 5 or less behave as a unified ferroelectric, where the BaTiO3 and Mn-BiFeO3 layers are structurally and electronically coupled. Density functional theory calculations can explain the behavior of spontaneous polarization for the superlattices in this thin regime. We propose that a superlattice formation comprising two types of perovskite layers with different crystal symmetries opens a path to novel ferroelectrics that cannot be obtained in a solid solution system.

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Sakai, Yuki, and Susumu Saito. "Geometries and Electronic Structure of Graphene and Hexagonal BN Superlattices." MRS Proceedings 1407 (2012). http://dx.doi.org/10.1557/opl.2012.455.

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ABSTRACTRelative stabilities and electronic structure of graphene/h-BN superlattices are discussed in the framework of the density functional theory. Most importantly, relative stabilities between commensurate and incommensurate superlattices are studied. Commensurate graphene/h-BN monolayer superlattices are found to be definitely more stable than incommensurate superlattices. In graphene/h-BN bilayer superlattices, commensurate superlattices are found to be slightly more stable than incommensurate superlattices. Results also imply that a finite pressure can induce transition from an incommensurate superlattice to a commensurate superlattice.

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Kumakura, Kazuhide, Toshiki Makimoto, and Naoki Kobayashi. "High Room-Temperature Hole Concentrations above 1019 cm−3 in Mg-Doped InGaN/GaN Superlattices." MRS Proceedings 622 (2000). http://dx.doi.org/10.1557/proc-622-t5.11.1.

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ABSTRACTWe achieved high hole concentrations above 1019 cm−3 at room temperature in Mg-doped InxGa1-xN/GaN (4 nm/4 nm) superlattices grown by metalorganic vapor phase epitaxy. The hole concentrations for the InxGa1-xN/GaN superlattices increased with the In mole fraction, and the maximum hole concentration reached 2.8 Å 1019 cm−3 for the In0.22Ga0.78N/GaN superlattice. The hole concentrations for the superlattices strongly depend on the structural parameters of the superlattices. The band bending due to the strain-induced piezoelectric field and the valence band structures of the InGaN/GaN heterostructures affect the hole generation in the superlattices. The weak temperature dependence of the resistivities for the InGaN/GaN superlattices with higher In mole fractions indicates highly efficient hole generation in the superlattice.

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46

Rodríguez-González, Rogelio, Heraclio García-Cervantes, Francisco Javier García-Rodríguez, Gerardo Jesús Escalera Santos, and Isaac Rodríguez-Vargas. "Extended states in random dimer gated graphene superlattices." Journal of Physics: Condensed Matter, May 22, 2024. http://dx.doi.org/10.1088/1361-648x/ad4f3c.

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Abstract Ordered and disordered semiconductor superlattices represent structures with completely opposed properties. For instance, ordered superlattices exhibit extended Bloch-like states, while disordered superlattices present localized states. These characteristics lead to higher conductance in ordered superlattices compared to disordered ones. Surprisingly, disordered dimer superlattices, which consist of two types of quantum wells with one type always appearing in pairs, exhibit extended states. The percentage of dissimilar wells does not need to be large to have extended states. Furthermore, the conductance is intermediate between ordered and disordered superlattices. In this work, we explore disordered dimer superlattices in graphene. We calculate the transmission and transport properties using the transfer matrix method and the Landauer-Büttiker formalism, respectively. We identify and discuss the main energy regions where the conductance of random dimer superlattices in graphene is intermediate to that of ordered and disordered superlattices. We also analyze the resonant energies of the double quantum well cavity and the electronic structure of the host gated graphene superlattice, ﬁnding that the coupling between the resonant energies and the superlattice energy minibands gives rise to the extended states in random dimer gated graphene superlattices.

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47

Schuller, Ivan K., Eric E. Fullerton, H. Vanderstraeten, and Y. Bruynseraede. "Quantitative X-Ray Structure Determination of Superlattices and Interfaces." MRS Proceedings 229 (1991). http://dx.doi.org/10.1557/proc-229-41.

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AbstractWe present a general procedure for quantitative structural refinement of superlattice structures. To analyze a wide range of superlattices, we have derived a general kinematical diffraction formula that includes random, continuous and discrete fluctuations from the average structure. By implementing a non-linear fitting algorithm to fit the entire x-ray diffraction profile, refined parameters that describe the average superlattice structure, and deviations from this average are obtained. The structural refinement procedure is applied to a crystalline/crystalline Mo/Ni superlattices and crystalline/amorphous Pb/Ge superlattices. Roughness introduced artificially during growth in Mo/Ni superlattices is shown to be accurately reproduced by the refinement.

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Hansen, Monica, Amber C. Abare, Peter Kozodoy, Thomas M. Katona, Michael D. Craven, Jim S. Speck, Umesh K. Mishra, Larry A. Coldren, and Steven P. DenBaars. "Effect of AlGaN/GaN Strained Layer Superlattice Period on InGaN MQW Laser Diodes." MRS Proceedings 595 (1999). http://dx.doi.org/10.1557/proc-595-f99w1.4.

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AbstractAlGaN/GaN strained layer superlattices have been employed in the cladding layers of InGaN multi-quantum well laser diodes grown by metalorganic chemical vapor deposition (MOCVD). Superlattices have been investigated for strain relief of the cladding layer, as well as an enhanced hole concentration, which is more than ten times the value obtained for bulk AlGaN films. Laser diodes with strained layer superlattices as cladding layers were shown to have superior structural and electrical properties compared to laser diodes with bulk AlGaN cladding layers. As the period of the strained layer superlattices is decreased, the threshold voltage, as well as the threshold current density, is decreased. The resistance to vertical conduction through p-type superlattices with increasing superlattice period is not offset by the increase in hole concentration for increasing superlattice spacing, resulting in higher voltages.

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Schuller, Ivan K. "Magnetic Superlattices." MRS Proceedings 103 (1987). http://dx.doi.org/10.1557/proc-103-335.

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ABSTRACTMagnetic superlattices serve as model systems for the study of thin film, interfacial, proximity, coupling and superlattice phenomena. Due to these phenomena, the physical properties of magnetic superlattices can be tuned in a reproducible fashion by proper control of the preparation process.Magnetic measurements in conjunction with detailed structural characterization provide a fruitful area of research, especially in understanding basic phenomena in magnetism. We describe here briefly a few experimental examples from our work which illustrate the possibilities magnetic superlattices offer for the study of basic phenomena in magnetism.

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Park, K., L. Salamanca-Riba, and B. T. Jonker. "Structural Studies Of (ZnSe/FeSe) Superlattices By Transmission Electron Microscopy." MRS Proceedings 238 (1991). http://dx.doi.org/10.1557/proc-238-683.

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ABSTRACTThe structural properties of (ZnSe/FeSe) superlattices, grown with and without a ZnSe buffer layer on (001) G a As substrates by molecular beam epitaxy, have been studied by transmission electron microscopy. High quality (ZnSe/FeSe) superlattices are obtained when grown on a ZnSe buffer layer on (001) GaAs substrates. In contrast, nominal (ZnSe/FeSe) superlattices grown directly on (001) GaAs substrates without a buffer layer showed evidence for intermixing of the layers in the superlattice indicating that the superlattice is unstable. We observed a disordered structure and an ordered structure in the resulting Zn1−xFexSe solid solution. The ordered structure corresponds to chemical ordering of Zn and Fe atoms along the < 100 > and < 110 > directions. We have studied the effect of misfit strain in the (ZnSe/FeSe) superlattices on the film quality.

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Journal articles on the topic 'Superlattices'

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