Formation of multilayer strained-layer heterostructures by liquid epitaxy. I. Theoretical aspects of the problem and mathematical model

Problems concerned with the formation of multilayer strained-layer heterostructures by “capillary” liquid-phase epitaxy with forced hydraulic replacement of the solutions in the growth channel are analyzed. It is shown for short contact times between the solutions and the crystallization surface that the character of their flow in the channel plays an important role in the achievement of uniformity in the physical characteristics of the layers grown. Theoretical estimates of the hydrodynamic stability of solutions moving in narrow channels are performed for several III-V systems. A mathematical model, which permits simulation of the conditions under which strained-layer heterostructures are fabricated, is developed. It takes into account diffusive and convective mass transport in the liquid for various flow regimes in the capillary and the displacement of the heterogeneous equilibria in the system under the influence of elastic stresses. Zh. Tekh. Fiz. 67, 42–49 (July 1997)     

High-temperature photoluminescence of CdHgTe solid solutions grown by molecular-beam epitaxy

The spectra of the high-temperature (up to 300 K) photoluminescence of the heteroepitaxial structures based on the CdHgTe solid solutions that are grown using molecular-beam epitaxy and emit at room temperature in the wavelength interval λ = 1.5–4.3 μm are analyzed. It is demonstrated that the observed photoluminescence of the CdHgTe narrow-gap semiconductor at high temperatures and the specific features of the high-temperature spectra can be interpreted using the disorder of the solid solution as in the case of the solid solutions of the group-III nitrides.     

Optical and X-ray diffraction studies of multilayer structures based on InGaN/GaN solid solutions

Multilayer structures based on the In _x Ga_{1 ? x} N/GaN compounds grown by gas-phase epitaxy from organometallic compounds are studied using photoluminescence spectroscopy and high-resolution X-ray diffraction. A method for analyzing the experimental rocking curves of multilayer structures in terms of the Parratt-Speriosu model is developed. This method permits one to determine the thickness, period, and average composition of In _x Ga_{1 ? x} N/GaN layers, as well as the deformation of the active region in the samples under study. The local indium content is determined using the theoretical model which describes the radiation energy as a function of the thicknesses of the InGaN layers taking into account the energy of quantum confinement, the energies of the spontaneous polarization and piezoelectric polarization, and the parameters determined from high-resolution X-ray diffraction data.     

Optical properties of multilayer heterostructures based on zinc chalcogenides upon strong laser excitation

We have carried out an experimental study of the nonlinear optical properties of multilayer heterostructures based on zinc chalcogenides when excited by ultrashort laser pulses. We have observed a strong change in the optical properties of the samples over a broad spectral region for two-photon and one-photon excitation of the ZnSe sublattice. The fast relaxation time of the nonlinearity is ∼2–5 psec in both cases. We propose a physical model qualitatively explaining the observed effects. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 805–809, November–December, 2007.     

Formation of copper/gold solid solutions by ion beam mixing

The formation of copper/gold solid solutions due to ion beam mixing was studied by Rutherford backscattering, high-voltage electron microscopy and transmission high-energy electron diffraction. Irradiation of multilayered Cu/Au thin films were performed with Xe⁺ ions or Ar⁺ ions at room temperature to doses ranging from 5×10¹⁵ to 2.5×10¹⁶ ions/cm² and energies from 100 to 300 keV. The ion beam mixing leads to uniformly mixed metal layers. The grain size of mixed layers is pronounced increase. It was found that Cu/Au solid solutions are formed with different composition in dependence on itinial composition and implantation dose. Cu-rich and Au-rich solid solutions are induced by ion beam mixing at an initial composition Cu _x Au_100–x withx70. In addition to these solid solutions, a solid solution of middle composition Cu₆₀...₄₀Au₄₀...₆₀ is formed for an initial composition withx<70. The kinetics of formation of solid solution is discussed as a function of the initial composition and implantation dose. Post-annealing experiments of mixed Cu₅₀Au₅₀ multilayers lead to lattice transformations and provide a superlattice structure CuAuI of the L1₀-type. With this process of ordering is associated the formation of dislocation loops.     

Electron probe microanalysis and local cathodoluminescence studies of multilayer heterostructures based on InGaN/GaN

This paper presents the results of the study on multilayer heterostructures based on InGaN/GaN grown by MOCVD. A new procedure to measure the composition and depth of InGaN quantum wells and AlGaN barrier layers is developed. Features of luminescence from different depths of the multilayer heterostructure are analyzed.     

Spontaneous and stimulated emission in the mid-ultraviolet range of quantum-well heterostructures based on AlGaN compounds grown by molecular beam epitaxy on c-sapphire substrates

This paper reports on the results of investigations of the spontaneous and stimulated luminescence in AlGaN heterostructures with a single quantum well and a high Al content (up to ～80 mol % in barrier layers), which were grown by plasma assisted molecular beam epitaxy (PAMBE) on c-sapphire substrates. It has been demonstrated that the stimulated emission occurs in the mid-ultraviolet range of the spectrum at wavelengths of 259, 270, and 289 nm with threshold excitation power densities of 1500, 900, and 700 kW/cm², respectively. It has been shown that there exists a possibility of TE polarization (E ⊥ c) of both stimulated and spontaneous luminescence down to wavelengths of 259 nm.     

Formation of superconductive supersaturated TaZr solid solutions by pulsed electron beam treatment

Amorphous TaZr films were prepared by simultaneous evaporation onto sapphire substrates. Pulsed electron beam treatment with deposited energy densities above a threshold of about 2 J cm^?2 led to a crystallization of the films and to the formation of supersaturated TaZr solid solutions with a bcc structure up to Zr concentrations of 54 at %. The crystalline alloys were superconducting with a maximum transition temperature T_c of 7.7 K. The films decomposed totally at a temperature of 1100°C during furnace annealing.     

Generation of high-frequency oscillations by electromagnetic shock wave on transmission lines on the basis of multilayer heterostructures

The possibility of the direct effective transformation of a videopulse into a radiopulse with high filling frequency (of the order of 100÷300 GHz) because of evolution of an electromagnetic shock wave structure on dispersive transmission lines with nonlinear components on the basis of multilayer heterostuctures (MLHS) with hysteretic (asymmetric MLHS) and single-valued functional (symmetric MLHS) capacitance — voltage characteristics has been investigated. The requirements on the MLHS and dispersion characteristics for effective generation of the train of oscillations are discussed.     

Raman study of the segregation of GaAs/AlAs heterostructures grown by molecular beam epitaxy

The Raman spectra of the optical confined phonons in the GaAs/AlAs ultra-thin layer superlattices grown with different growth conditions were used to determine the compositional profiles and to study the process of segregation at the heterointerfaces. A modified kinetic model was developed in order to calculate the compositional profiles in the samples under investigation. The comparison between the experimentally obtained compositional profiles and those calculated by the kinetic model allowed us to determine the parameters characterizing the segregation. It was shown that the increase of pressure of As acts equivalently to the decrease of the growth temperature, resulting in a more abrupt compositional profile.     

Structural and electrical performance of epitaxial InP based heterojunctions prepared by liquid phase epitaxy

Thin films of InP was grown on single crystalline substrates of Si to form InP/Si heterojunctions by liquid phase epitaxy (LPE) and its morphology and crystalline characteristics were achieved. The essential electrical properties and its main parameters were extracted using the current density-voltage. The analysis was done to obtain the rectification characteristics which has its maximum value at a certain voltage of 0.7 V. Moreover, the heterojunction obeys ohmic behavior followed by quadratic space charge limited conduction at lower and higher voltage regions, respectively. The conductivity under AC bias as well as the dielectric behaviors of the heterojunction was explored in the frequency range 100 kHz–5 MHz and in the temperature range 298–623 K. The AC conductivity is interpreted by the correlated barrier hopping model via single polaron with activation energy dependent on the applied frequency. The response of the dielectric constants confirms its remarkable dependence on both frequency and temperature.     

Diagnostics of heterostructures of resonant-tunneling diodes during epitaxial growth. II. Monitoring techniques based on reflection method

It is shown that the reflection methods, in particular, the reflection anisotropy method, can be efficiently used for in situ studying and monitoring the growth of heterostructures with layers thinner than 10 monolayers. A change in the layer composition at direct GaAs/AlAs heterointerfaces of the active region of the resonant-tunneling diode is recorded by the reflection anisotropy method with a thickness resolution of ～1 monolayer immediately during the growth. To estimate the quality of the formed active region of the resonant-tunneling diode, comparative reflection anisotropy spectroscopy is used.     

一种基于金刚石多层波导结构微环谐振器的仿真分析

提出了一种以金刚石新型材料为芯层的单微环谐振器模型.谐振器的纵切面采用五层脊形波导结构,中间一层设定为金刚石,上下两侧分别是SiO_2和As_2S_3,即As_2S_3-SiO_2-金刚石-SiO_2-As_2S_3.设置操作波长为1550 nm,依据耦合膜理论和微环谐振理论,利用Comsol软件仿真模拟了单直波导纵切面、直波导和环形波导耦合区的纵切面以及微环在谐振波长为1543 nm时的场强分布,及直波导和环形波导耦合区间距改变时微环的场强分布和传输特性.在此基础上,依据传输矩阵法讨论了微环的品质因数、耦合系数变化对输出光谱的影响,并对微环损耗进行了讨论.结果表明:以金刚石为芯层的微环谐振器具有良好的光学特性,本结构在谐振波长为1543 nm时谐振峰值达到了-12 dB以上,品质因数达到了1.54×10~5,在耦合系数为0.01时,自由光谱范围约为40 nm.     

Formation of spin light-emitting diodes based on InGaAs/GaAs heterostructures containing ferromagnetic inclusions

The electroluminescence of light-emitting diodes based on heterostructures with InGaAs quantum wells and a delta 〈Mn〉 doped layer in the GaAs barrier is studied. It is shown that the diodes emit circularly polarized light with the degree of polarization depending on the applied magnetic field and on temperature. We assume that the temperature dependences of the degree of polarization are determined by a change in the mutual position of energy levels of Mn ions in the delta layer and of holes in a quantum well.