MICROSTRUCTURE AND LUMINESCENCE PROPERTIES OF GaxIn1-xP/GaAs HETEROSTRUCTURE

The Ga_xIn_1-xP/GaAs heterostructures with different x values have been investigated by photoluminescence (PL), energy dispersive spectrum (EDS), and transmission electron microscopy (TEM). Experimental results suggested that the composition of epitaxial layers evidently affected the microstructure of the heterostructures. When x value was close to 0.5, the defects in the epitaxial layer decreased, and the lattice match between film and sub-strate approached optimum, Meanwhile, the heteroatructure provided a high luminescence efficiency.     

Orientation-patterned templates GaAs/Ge/GaAs for nonlinear optical devices. I. Molecular beam epitaxy

GaAs/Ge/GaAs heterostructures in which the GaAs layer lattice on Ge is rotated at a right angle to the substrate plane are grown by molecular-beam epitaxy (MBE). Such heterostructures are grown in different epitaxial setups for GaAs and for Ge with wafer transfer through air tor the first time. It is proposed to use surfactants (Bi, Sb) to control GaAs layer nucleation on Ge.     

A thin film perspective on quantum functional oxides

Transition metal oxides show remarkably diverse quantum functional properties such as high temperature superconductivity, colossal magnetoresistance, multiferroicity, two-dimensional electron gas, and topological insulators. This diversity manifests as a result of many energy scales of similar magnitude competing rather than any particular one dominating in the system. In this regard, growth of atomically controlled epitaxial thin films and heterostructures would allow to control relevant energy scales by imposing various stimuli, such as reduction of dimensionality, introduction of interfaces, modification of the interfacial octahedral tilts, and symmetry breaking; in turn, modified functional properties or completely new phenomena may emerge in epitaxial thin films and heterostructures. Also of exceeding importance is the fact that atomically controlled epitaxial thin films and heterostructures of the multifunctional oxides offer promising potentials for next generation oxide electronics. In this short review, we collect representative examples of quantum correlated phenomena arising in epitaxial films and heterostructures of transition metal oxides and highlight some of the progresses achieved in thin film research of various functional oxides in the last couple of decades.     

Mechanisms of dislocation generation in Si structures with strained layers: Intrinsic point defects in dislocation nucleation

The peculiarities of dislocation production in silicon compositions with elastically strained layers fabricated by the molecular-beam epitaxy technique (SiGe/Si heterostructures) and by direct bonding of Si(110)/Si(100) wafers are studied with transmission electron microscopy. The role of intrinsic point defects during the process of nucleation of misfit dislocations is explained. The surplus concentration of these defects in heterostructures was produced via low-temperature epitaxial growth of buffer layers or with ion implantation of elastically strained heterostructures. The model of “optimal” and “inverse” intrinsic point defects providing an explanation for the relaxation of misfit strains in heterostructures is proposed.     

Magnetoresistance of structures with MnAs layers and <Emphasis Type="Italic">A</Emphasis><Superscript>3</Superscript><Emphasis Type="Italic">B</Emphasis><Superscript>5</Superscript> semiconductors heavily doped with manganese

The magnetotransport properties of epitaxial ferromagnet/semiconductor heterostructures based on MnAs and GaMnAs ferromagnetic layers, separated by a nonmagnetic semiconductor layer (InAs or GaAs), have been investigated. Structures were obtained by combination of laser deposition and metal-organic chemical vapor deposition. A spin-valve effect was observed in magnetoresistance measurements. This fact suggests spin-polarized transport of carriers between ferromagnetic layers.     

晶体相场法模拟异质外延过程中界面形态演化与晶向倾侧

采用晶体相场模型研究了异质外延过程中失配应变与应力弛豫对外延层界面形态演化的影响, 并对由衬底倾角引起的外延层晶向倾侧进行了分析.研究结果表明: 在有一定倾角的衬底晶体上进行外延生长时,若衬底和外延层之间失配度较大 (ε>0.08),外延层中弹性畸变能会以失配位错的形式释放, 最终薄膜以稳定的流动台阶形式生长且外延层的晶向倾角与衬底倾角呈近似线性关系. 而当衬底和外延层之间失配度较小(ε<0.04)不足以形成失配位错时, 外延层中弹性畸变能会以表面能的形式释放,最终使薄膜以岛状形态生长. 在高过冷度条件下,衬底倾角和失配度较大时,衬底和外延层之间会形成由大量位错规则排列而成的小角度晶界从而显著改变外延层的生长位向.     

Dielectric Parameters of Elastically Strained Heteroepitaxial SrTiO3 Films

Physics of the Solid State - Three-layer epitaxial SrRuO3/SrTiO3/SrRuO3 heterostructures with the 900-nm-thick intermediate layer of strontium titanate have been grown on single-crystal...     

Degradation mechanism of two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures

This paper finds that the two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures exhibits an obvious time-dependent degradation after the epitaxial growth. The degradation mechanism was investigated in depth using Hall effect measurements, high resolution x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. The results reveal that the formation of surface oxide is the main reason for the degradation, and the surface oxidation always occurs within the surface hexagonal defects for high Al-content AlGaN/GaN heterostructures.     

Rearrangement of Electroluminescence Spectra in Type-II n-InAs/n-InAsSbP Heterostructures

Physics of the Solid State - Single heterostructures of type II n+-InAs/n0-InAs0.59Sb0.16P0.25, based on an intentionally undoped epitaxial layer with an electronic type of conductivity are...     

Pulsed laser deposition of lead-zirconate-titanate thin films and multilayered heterostructures

There is an increasing interest in lead-zirconate-titanate (PZT) based ferroelectric thin film and devices in recent years. Pulsed laser deposition (PLD) technique has been demonstrated to be a versatile and successful tool for the deposition of epitaxial multi-component metal oxide films and heterostructures. This review presents a reasonable understanding of the relationship between PLD processing and composition, crystal structure and orientation of PZT ferroelectric thin films, and heterostructures. Processing-related issues from PLD of PZT thin films and material-integration strategies developed to fabrication of highly oriented or epitaxial PZT thin film based capacitors with excellent ferroelectric properties are discussed in detail. PACS 81.15.Fg; 68.55.Jk; 77.22.Ej     

Thermophotovoltaic converters on indium arsenide-based compounds

Thermophotovoltaic converters based on multicomponent solid solutions of III–V compounds, specifically, InAsSbP/InAs heterostructures (E _g = 0.35–0.60 eV), that are intended for fabricating IR emitters heated to 1000–2000°C are studied. The use of such narrow-gap heterostructures makes it possible to advance the sensitivity of the elements into the long-wave range and utilize the thermal energy of low-temperature sources more efficiently. Fresh physical approaches to fabricating epitaxial quaternary InAs-based InAsSbP solid solutions with a low carrier concentration and heterostructures with sharp interfaces are presented. Quaternary InAsSbP solid solutions and other related heterostructures offer a number of advantages, such as the possibility of growing perfect structures lattice-matched with the substrate, stress-free interfaces, good electrical and photoelectrical properties (low dark currents and a high external quantum efficiency), and the possibility of flexibly controlling the energy gap by varying the composition of the solid solution. It is shown that InAsSbP films grown on an InAs substrate by liquid-phase epitaxy from supercooled liquid solution and liquid-phase electro-epitaxy with replenishment of liquid solution by growing layer components are uniform in composition and have a perfect crystal structure. Thermophotovolatic p-InAsSbP/n-InAs diode-type heterostructures obtained by the above methods are found to have saturation dark currents close to theoretically predicted values and a wide range of spectral sensitivity, which makes them candidates for thermophotovoltaic elements.     

Magnetic and Resistive Properties of Magnetite/Iridate Heterostructures

Journal of Experimental and Theoretical Physics - A technique is developed to grow epitaxial heterostructures consisting of strontium iridate (SrIrO3) and lanthanum–strontium manganite...     

Defect formation in Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>/Ge(111) epitaxial heterostructures

Selective chemical etching and transmission electron microscopy are used to study the defect formation in Ge_1?xSi_x/Ge(111) epitaxial heterostructures at 0.01<x<0.35. As the Si content in the solid solution (SS) increases, the dislocation densities in the epitaxial layer, at the interface, and in the near-interface region in the substrate are found to vary nonmonotonically. The difference in the depth distribution of dislocations observed in the heterostructures in three different SS composition ranges is caused by the effect of the SS composition on the kinetics of misfit-stress relaxation, in particular, on the intensity of misfit-dislocation generation and multiplication. It is found that, in the heterostructures grown by hydride epitaxy at 600°C, misfit-dislocation multiplication through a modified Frank-Read mechanism occurs only in the range 0.03<x<0.20. The results obtained are explained in the context of the effect of silicon-rich microprecipitates, which form during the spinodal decomposition of the SS, on dislocation generation and motion in the epitaxial layer. A mechanism is proposed for misfit-dislocation generation by heterogeneous sources in the epitaxial layer; the mechanism is based on the generation of interstitial dislocation loops near microprecipitates.     

Atomic Force Microscopy Examination of Elementary Processes in Metalorganic Compound Hydride Epitaxy of GaAs-Based Nanoheterostructures

Technical Physics - Elementary processes involved in low-pressure metalorganic compound hydride epitaxial growth of (Al, Ga, In)As heterostructures on misoriented GaAs(001) substrates have been...     

Epitaxial ferromagnetic thin films and heterostructures of Mn-based metallic and semiconducting compounds on GaAs

We present two approaches to integrate magnetic materials with III–V semiconductors. One is epitaxial ferromagnetic metallic films and heterostructures on GaAs (0 0 1) substrates. Although crystal structure, lattice constant, chemical bonding and other properties are dissimilar, ferromagnetic hexagonal MnAs thin films and MnAs/NiAs ferromagnet/nonmagnet heterostructures (HSs) are grown on GaAs by molecular beam epitaxy (MBE). Multi-stepped magnetic hysteresis are controllably realized in MnAs/NiAs HSs, making this material promising for the application to multi-level nonvolatile recording on semiconductors. The other approach is to prepare a new class of GaAs based magnetic semiconductor, GaMnAs, by low-temperature molecular beam epitaxy (LT-MBE) on GaAs (0 0 1). New III–V based superlattices consisting of ferromagnetic semiconductor GaMnAs and nonmagnetic semiconductor AlAs are also successfully grown. Structural and magnetic properties of these new heterostructures are presented.     

Effect of preferred orientation on magnetoelectric properties of multiferroic La0.7Sr0.3MnO3/BaTiO3 heterostructure

The epitaxial La_0.7Sr_0.3MnO₃/BaTiO₃ bilayer heterostructures were deposited on LaAlO₃ (001) and (110) substrates by pulsed laser deposition. The inherent ferromagnetic, ferroelectric properties and strong magnetoelectric (ME) effect at room temperature were approved, which correlated to the preferred orientation of the films. Both heterostructures showed similar frequency-dependent ME behavior in 0.1 kHz-100 kHz, the ME voltage coefficients were around 140 mV/cm Oe and 104.8 mV/cm Oe at 1 kHz for (001) and (110) oriented bilayers, respectively. This was at least one order of magnitude higher than previously reported results of the related heterostructures, which is mainly ascribed to the lower dielectric constant of BTO film.     

Oscillatory exchange coupling and positive magnetoresistance in epitaxial oxide heterostructures

Oscillation in the exchange coupling between ferromagnetic La(2/3)Ba(1/3)MnO3 layers with paramagnetic LaNiO3 spacer layer thickness has been observed in epitaxial heterostructures of the two oxides. This behavior is explained within the RKKY model employing an ab initio calculated band structure of LaNiO3, taking into account strong electron scattering in the spacer. Antiferromagnetically coupled superlattices exhibit a positive current-in-plane magnetoresistance.     

Source of Indistinguishable Single Photons Based on Epitaxial InAs/GaAs Quantum Dots for Integration in Quantum Computing Schemes

JETP Letters - The characteristics of single photons emitted by columnar microstructures based on epitaxial microcavity heterostructures with distributed Bragg reflectors, which include...     

Ultrafast strain engineering in complex oxide heterostructures

We report on ultrafast optical experiments in which femtosecond midinfrared radiation is used to excite the lattice of complex oxide heterostructures. By tuning the excitation energy to a vibrational mode of the substrate, a long-lived five-order-of-magnitude increase of the electrical conductivity of NdNiO(3) epitaxial thin films is observed as a structural distortion propagates across the interface. Vibrational excitation, extended here to a wide class of heterostructures and interfaces, may be conducive to new strategies for electronic phase control at THz repetition rates.     

Design,nano-fabrication and analysis of near-infrared 2D photonic crystal air-bridge structures

Selective wet etching is a technique that allows fabrication of freely suspended thin slabs in epitaxial heterostructures. This technique, together with high-aspect ratio dry etching, is used to create two-dimensional (2D) photonic crystals for near-infrared wavelengths in thin suspended AlGaAs membranes. The active photonic crystal areas contain hexagonal arrays of cylindrical holes completely perforating the membrane. For an appropriate selection of the slab thickness and the lattice parameter, dispersion relations for the guided modes are explicitly computed by solving the Maxwell equations in a geometry containing a 2D photonic crystal defined in the core layer of a dielectric waveguide structure. Measurements of the spectral transmittance in air-bridge samples show a narrow 30-dB-deep stop band for TM polarized incident light. The spectral position of the stop band shows a good agreement with theoretical band structure calculations when also the quasi-guided resonant modes outside the light cone are taken into account.