分子束外延生长Fe/Fe_(50)Mn_(50)双层膜的交换偏置

利用表面磁光克尔效应和铁磁共振对分子束外延生长的Fe/Fe50Mn50双层膜的交换偏置场和矫顽力进行了研究,实验结果表明,当反铁磁层厚度小于5.5!nm时,不出现交换偏置,而当大于这一厚度时,出现交换偏置;大约在7!nm时,达到极大值.随着反铁磁层厚度的继续增大,偏置场和矫顽力随Fe50Mn50膜厚的增大而下降.铁磁共振实验结果表明样品的磁性存在单向各向异性.并对上述结果进行了讨论.     

MBE-grown Ridge-waveguide InGaAs/InGaAsP Strained Quantum Well Lasers at 2 μm Wavelength

The result of molecular beam epitaxy (MBE)-grown ridge-waveguide InGaAs/ InGaAsP/InP strained quantum well lasers at 2 μm wavelength is reported. The pulsed electrical luminescence spectrum at room temperature is observed with peak wavelength of about 1.98 μm. At 77 K the lasers become lasing in pulse regime, with threshold current of about 18～30 mA, peak wavelength of about 1.87～ 1. 91 μm, and single longitudinal mode operation in the current range of 160～230 mA.     

Molecular beam epitaxy of Ca1−xRxF2+x (R=Nd, Er) layers: study of RHEED pattern and lattice mismatch

Ca_1−xNd_xF_2+x and Ca_1−xEr_xF_2+x layers were grown on CaF₂(1 1 1) substrates at 600 and 550°C, respectively, by molecular beam epitaxy. Reflection high-energy electron diffraction (RHEED) investigation revealed that Ca_1−xNd_xF_2+x layers have two types of surface structure, namely (1×1) and ( )R30⁰ with hexagonal symmetry, depending on Nd mole fraction, while Ca_1−xEr_xF_2+x layers have three types of surface structure, namely (1×1) and (2×2) with hexagonal symmetry, and a triple rotated domain structure based on a rectangular cell depending on Er mole fraction. The lattice mismatch of the epilayers and substrate, which is important for applications involving buffer layers, was measured by X-ray rocking curve (XRC) analysis.     

Densely packed Ge quantum dots grown on SiO2/Si substrate

We studied the growing process of Ge dots on silicon substrates covered with an ultrathin silicon dioxide buffer layer which was formed with simple chemical procedure. Uniform and densely packed (10¹¹ cm⁻²) quantum dots (QDs) were obtained by optimizing the growth parameter with the MBE method. The influence of temperature, coverage, as well as the post-annealing process, on the epitaxial and non-epitaxial nanodots formation was evaluated. Nano-sized high density quantum dots were also realized with different growing conditions, whose structural and growing mechanism were discussed under the help of SEM and RHEED results.     

Two-dimensional lateral ordering of self-assembled Ge islands on patterned substrates

Stacks of Ge islands layers, separated by thin Si spacer layers, have been grown on prepatterned Si (0 0 1) substrates. The sample topography, obtained by atomic force microscopy, exhibits a regular two-dimensional island arrangement. The vertical alignment is confirmed in cross-sectional transmission electron microscopy images. X-ray diffraction reciprocal space maps around the (0 0 4) Bragg point reveal exceptional lateral and vertical ordering of the Ge islands. Photoluminescence spectra taken at 5 K show well-separated peaks of the no-phonon and the transverse-optical phonon replica of these ordered islands, which is achieved too, due to the excellent island size uniformity.     

低温生长的Ge/Si超晶格界面结构的X射线散射研究

低温下用MBE方法生长了Ge/Si超晶格,X射线反射及横向散射研究表明,Ge亚层上下表面的粗糙度呈反对称,下表面大的粗糙度来源于Ge向Si亚层中扩散形成SiGe混合组分结构,这种组分结构可以用一平均成分的SiGe合金层加以拟合,从而使得各亚层均有一个合理的粗糙度,旋转样品进行的X射线散射研究表明,这种SiGe的混合是各向同性的,这与透射电子显微镜的研究结构相一致.     

As保护下的生长中断时间对AlSb/InAs超晶格界面粗糙度的影响

用分子束外延设备(MBE)在GaAs(100)衬底上生长了InSb型界面的AlSb/InAs超晶格，界面生长过程中采用了As保护下不同的中断时间.运用掠入射X射线反射技术(GIXRR)对样品进行了测量，并对测量结果进行了模拟和分析，发现As保护下生长中断20 s能获得最平整的AlSb/InAs界面.结合分析显微镜下观察到的样品形貌，过短的界面中断时间会导致界面富In并形成In点，而过长的中断时间会导致AlAs型界面的形成，两者都使界面变得粗糙.另外，还讨论了生长中断在分子束外延生长中的应用. 关键词： 分子束外延 生长中断 超晶格 掠入射X射线反射     

Highly-ordered SiGe-islands grown by dislocation patterning using ion-assisted MBE

Fabrication of device structures based on laterally self-ordered systems without the use of expensive and time-consuming nanolithography could have undoubted advantages. For such applications, it is proposed to use misfit dislocation networks from partially relaxed SiGe layers on (1 0 0) Si substrate as a template for the growth of highly ordered SiGe islands. Ion bombardment during molecular beam epitaxy of metastable SiGe layers leads to such a partial relaxation by misfit dislocation networks. The ions are generated by the interaction of the evaporated Si flux with the electrons in an electron beam evaporator, which causes a partial ionization of Si atoms in the molecular beam. We demonstrate by atomic force microscopy that subsequent growth of SiGe on such relaxed SiGe (25-50% Ge) layers leads to the formation of uniform three-dimensional islands highly ordered in 〈1 1 0〉 directions.     

A Comparative Study of the Growth of Cr on (110)TiO2 Rutile, (0001) α-Al2O3 and (100)SrTiO3 Surfaces

Thin Cr films were deposited on single crystal -Al₂O₃, SrTiO₃ and TiO₂ (rutile) substrates under ultrahigh vacuum conditions using molecular beam epitaxy (MBE). The growth behavior and thermal stability of the films were investigated with scanning tunneling microscopy (STM), X-ray phototelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). Cr grew as 3D clusters on all substrates. For all three Cr/oxide systems a strong temperature dependent interfacial reaction was observed. The results suggested that these reactions depended greatly on thermodynamics and on transport properties in the oxide substrates.