Scaling behavior of the time-fractional equations for molecular-beam epitaxy growth: scaling analysis versus numerical stimulations

The scaling behavior of the time-fractional molecular-beam epitaxy (TFMBE) equations in 1+1 dimensions is investigated by numerical simulations and scaling analysis, respectively. The growth equations studied include the time-fractional linear molecular-beam epitaxy (TFLMBE) and the time-fractional Lai-Das Sarma-Villain (TFLDV). Growth exponents are obtained using the two methods. The analytical results are consistent with the corresponding numerical solutions based on Caputo-type fractional derivative.     

Anomalous Scaling of Surface Growth Equations with Spatially and Temporally Correlated Noise

Based on the scaling idea of local slopes by López et al. [Phys. Rev. Lett. 94 (2005) 166103], we investigate anomalous dynamic scaling of (d+1)-dimensional surface growth equations with spatially and temporally correlated noise. The growth equations studied include the Kardar-Parisi-Zhang (KPZ), Sun-Guo-Grant (SGG), and Lai-Das Sarma-Villain (LDV) equations. The anomalous scaling exponents in both the weak- and strong-coupling regions are obtained, respectively.     

1+1维Wolf-Villain模型奇异标度行为的数值模拟

采用Kinetic Monte Carlo(KMC)方法对描述分子束外延生长(MBE)的1+1维Wolf-Villain模型进行大尺寸和长生长时间的数值模拟研究,以消除渡越行为的影响.计算得到整体和局域标度指数.结果显示,在所模拟的空间和时间尺度范围内,1+1维Wolf-Villain模型仍呈现出固有奇异标度行为.这一结论与López等人最近的理论分析结果不一致.     

含时空关联噪声生长方程的标度奇异性分析

基于动力学重整化群理论研究表面界面生长动力学标度奇异性问题, 得到含时空关联噪声的表面生长方程标度奇异指数的一般结果,并将此方法应用于几种典型的局域生长方程——Kardar-Parisi-Zhang（KPZ）方程、线性生长方程、Lai-Das Sarma-Villain（LDV）方程.结果表明,在长波长极限下局域生长方程的动力学标度奇异性与最相关项、基底维数以及噪声有关,并且若出现标度奇异性,只会是超粗化（super rough）奇异标度行为,而不是内禀（intrinsically）奇异标度行为. 关键词： 标度奇异性 动力学重整化群理论 时空关联噪声     

含有广义守恒律的生长方程标度奇异性的直接标度分析

利用直接标度分析方法研究一个含有广义守恒律生长方程的标度奇异性,得到强弱耦合区域的奇异标度指数.作为其特殊情况,这个方程包含Kardar-Parisi-Zhang（KPZ）方程、 Sun-Guo-Grant（SGG）方程以及分子束外延（MBE）生长方程,并能对其进行统一的研究.研究发现, KPZ方程和SGG方程,无论在弱耦合还是在强耦合区域内都遵从自仿射Family -Vicsek正常标度规律;而MBE 方程在弱耦合区域内服从正常标度,在强耦合区域内能呈现内禀奇异标度行为.这里所得到生长方程的奇异标度性质与利用重正化群理论、数值模拟以及实验相符很好. 关键词： 标度奇异性 强耦合 弱耦合     

Anomalous dynamic scaling of the non-local growth equations

The anomalous dynamic scaling behavior of the d+1 dimensional non-local growth equations is investigated based on the scaling approach. The growth equations studied include the non-local Kardar-Parisi-Zhang (NKPZ), non-local Sun-Guo-Grant (NSGG), and non-local Lai-Das Sarma-Villain (NLDV) equations. The anomalous scaling exponents in both the weak- and strong-coupling regions are obtained, respectively. Our results show that non-local interactions can affect anomalous scaling properties of surface fluctuations.     

高质量稀磁半导体(Ga,Mn)Sb单晶薄膜分子束外延生长

理论预言窄禁带稀磁半导体(Ga,Mn)Sb及其异质结构可能存在量子反常霍尔效应等新奇特性, 近年来受到了特别关注. 但是, 由于(Ga,Mn)Sb薄膜生长窗口窄, 纯相(Ga,Mn)Sb薄膜制备比较困难, 迄今关于这类材料的研究报道为数不多. 本文采用低温分子束外延的方法, 通过优化生长条件, 成功制备出厚度为10 nm, Mn含量在0.016至0.039之间的多组(Ga,Mn)Sb薄膜样品. 生长过程中反射式高能电子衍射原位监测和磁性测量都表明没有MnSb等杂相的偏析, 同时原子力显微镜图像表明其表面形貌平滑, 粗糙度小. 通过生长后退火处理, (Ga,Mn)Sb薄膜的最高居里温度达到30 K. 此外, 本文研究了霍尔电阻和薄膜电阻随磁场的变化关系, 在低温下观测到明显的反常霍尔效应.     

Kinetic model for a step edge in epitaxial growth

A kinetic theory is formulated for the velocity of a step edge in epitaxial growth. The formulation involves kinetic, mean-field equations for the density of kinks and "edge adatoms" along the step edge. Equilibrium and kinetic steady states, corresponding to zero and nonzero deposition flux, respectively, are derived for a periodic sequence of step edges. The theoretical results are compared to results from kinetic Monte Carlo (KMC) simulations of a simple solid-on-solid model, and excellent agreement is obtained. This theory provides a starting point for modeling the growth of two-dimensional islands in molecular-beam epitaxy through motion of their boundaries, as an alternative to KMC simulations.     

Quick ellipsometric technique for determining the thicknesses and optical constant profiles of Fe/SiO2/Si(100) nanostructures during growth

An algorithm is developed to perform rapid control of the thickness and optical constants of a film structure during growth. This algorithm is tested on Fe/SiO₂/Si(100) structures grown in an Angara molecular-beam epitaxy setup. The film thicknesses determined during their growth are compared with X-ray spectral fluorescence analysis and transmission electron microscopy data.     

Surface reconstructions of MnAs grown on GaAs(001)

During epitaxial growth of MnAs on GaAs(001) by molecular-beam epitaxy (MBE) the surface exhibits various reconstructions depending on the growth conditions. These reconstructions have been studied during growth by reflection high-energy electron diffraction (RHEED) and reflectance difference spectroscopy (RDS). A feature sensitive to the surface structure was identified in the RD spectra. After growth, the (1×2) and (1×1) reconstructions were cooled down to room temperature and imaged in ultrahigh vacuum with a conventional scanning tunneling microscope (STM). Atomic-scale images of these surfaces are presented.     

Effect of growth conditions on photoluminescence of erbium-doped silicon layers grown using sublimation molecular-beam epitaxy

Erbium-doped epitaxial silicon layers were grown using two different growth techniques, namely, commonly used molecular-beam epitaxy (MBE) and solid-phase epitaxy (SPE). It is shown that an erbium-doped silicon epitaxial layer deposited through SPE on a cold substrate and subsequently annealed displays amore intense photoluminescence at a wavelength of 1.54 μm than do MBE-grown layers. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 1, 2004, pp. 102–104. Original Russian Text Copyright ? 2004 by Shengurov, Svetlov, Chalkov, Andreev, Krasil’nik, Kryzhkov.     

Growth and properties of ferromagnetic In1−xMnxSb alloys

We discuss a new narrow-gap ferromagnetic (FM) semiconductor alloy, In_1−xMn_xSb, and its growth by low-temperature molecular-beam epitaxy. The magnetic properties were investigated by direct magnetization measurements, electrical transport, magnetic circular dichroism, and the magneto-optical Kerr effect. These data clearly indicate that In_1−xMn_xSb possesses all the attributes of a system with carrier-mediated FM interactions, including well-defined hysteresis loops, a cusp in the temperature dependence of the resistivity, strong negative magnetoresistance, and a large anomalous Hall effect. The Curie temperatures in samples investigated thus far range up to 8.5 K, which are consistent with a mean-field-theory simulation of the carrier-induced ferromagnetism based on the 8-band effective band-orbital method.     

Heteroepitaxy of erbium-doped silicon layers on sapphire substrates

The possibility of using sublimation molecular-beam epitaxy as an efficient method for growing erbium-doped silicon layers on sapphire substrates for optoelectronic applications is analyzed. The advantage of this method is that the erbium-doped silicon layers can be grown at relatively low temperatures. The use of sublimation molecular-beam epitaxy makes it possible to grow silicon layers of good crystal quality. It is demonstrated that the growth temperature affects not only the structure of silicon-on-sapphire layers but also the crystallographic orientation of these layers. The electrical and luminescence properties of the erbium-doped silicon layers are discussed. It is revealed that structures of this type exhibit intense erbium photoluminescence at a wavelength of 1.54 μm.     

An STM study of molecular-beam epitaxy growth of GaAs

Scanning tunneling microscopy has been used to investigate molecular-beam epitaxy growth of GaAs. By quenching the sample during deposition, we have imaged the GaAs(001) surface as it appeared during growth. Large scale images of the surface have been obtained at coverages varying from 0.25 to 1500 layers.     

STUDY OF THE MECHANISM OF GaAs(001) MOLECULAR-BEAM EPITAXY

In this paper the nucleation and growth processes of GaAs(001) molecular-beam epitaxy were studied by Monte Carlo simulation, The density of islands and the density of isolated Ga adatoms were obtained for different growth temperatures, and the island size distribution at low coverage, as well as the correlation function between atoms and its relation with the temperature were studied in detail.     

SrTiO3同质外延过程中的反射高能电子衍射图案分析

在激光分子束外延实验中,用RHEED原位监测了SrTiO3基片初始、退火以及同质外延过程中的表面形态.通过对RHEED图案分析,获取了表面面内的晶格常数振荡与衍射条纹的半高宽振荡现象,前者是由退火重构表面与薄膜之间的界面造成的,后者与二维岛边界的弛豫相关.另外还观察到了等离子体对入射电子束的影响而导致的RHEED强度振荡行为的相位移现象. 关键词： 反射高能电子衍射 SrTiO3 表面晶格常数及衍射强度振荡     

MBE growth of AlGaAs on patterned GaAs substrates

We have experimentally and theoretically investigated the molecular-beam epitaxy growth of AlGaAs layers on ridge structures of patterned GaAs(0 0 1) substrates. While the surface morphologies were imaged by scanning electron microscopy, the local Al concentrations were mapped by spatially resolved micro-photoluminescence spectroscopy. Both, the surface morphologies and the profiles of the Al concentration could be well modeled by calculations based on a rate-equation which accounts for the migration of Ga adatoms and for the different growth rates of GaAs and AlAs.     

界面生长中断对GaAs (111)衬底上 AlGaAs/GaAs量子阱电子自旋寿命的影响

用固源分子束外延技术(SSMBE)在GaAs(111)衬底上,采用不同的界面中断时间生长了多组AlGaAs/GaAs多量子阱样品(MQWs),通过室温发光光谱和时间分辨克尔旋转谱(TRKR)研究了界面生长中断对发光光谱半峰全宽(FWHM)和量子阱中电子自旋弛豫时间(自旋寿命)的影响,发现了自旋寿命随着界面生长中断时间的增加呈现先减小后增加的趋势,此变化趋势与荧光光谱半峰全宽表征的材料质量随中断时间的变化一致,适当的界面生长中断时间能有效的增加GaAs (111)衬底上AlGaAs/GaAs 多量子阱中电子自旋寿命。     

Generic dynamic scaling in kinetic roughening

We study the dynamic scaling hypothesis in invariant surface growth. We show that the existence of power-law scaling of the correlation functions (scale invariance) does not determine a unique dynamic scaling form of the correlation functions, which leads to the different anomalous forms of scaling recently observed in growth models. We derive all the existing forms of anomalous dynamic scaling from a new generic scaling ansatz. The different scaling forms are subclasses of this generic scaling ansatz associated with bounds on the roughness exponent values. The existence of a new class of anomalous dynamic scaling is predicted and compared with simulations.     

Comparison of organic thin films deposited by supersonic molecular-beam epitaxy and organic molecular-beam epitaxy: The case of titanyl phthalocyanine

Recently, supersonic molecular-beam epitaxy (SuMBE) was invented as an alternative method for the deposition of organic material, using higher kinetic energies for deposition than conventional organic molecular-beam epitaxy (OMBE). Using titanyl phthalocyanine (TiOPc) as a model substance, we show that the SuMBE deposition results in increased crystal quality of the deposited material. This is induced by the high kinetic energy of the molecular-beam in SuMBE, which leads to increased molecular mobility on the surface, resulting in larger crystal sizes and higher crystal quality. Alternatively, similar films as made by OMBE can be deposited by SuMBE at lower substrate temperatures. This temperature reduction may be of interest for the deposition of stacked organic devices on underlying heat sensitive layers, as they are quite common in organic electronic devices.