在Si衬底上用分子束外延低温生长Ge薄膜

本文报道了室温下淀积的薄层Ge在Si衬底表面上通过加热形成结晶的Ge岛,然后在此“带结构”的衬底表面上用分子束外延(MBE)方法生长Ge薄膜的反射式高能电子衍射(RHEED),俄歇电子能谱(AES)研究结果。X射线双晶衍射的测试结果表明,衬底表面的Ge岛有助于释放外延层的失配应力,提高外延层的晶体质量。 关键词：     

关于RHEED振荡技术优化GaAs(110)量子阱生长的研究

在GaAs(110)衬底上生长的半导体材料有诸多优良性能，使得在非极性GaAs(110)衬底上获得高质量各类异质结材料，成为近年来分子束外延生长关注的课题.考虑GaAs(110)表面是Ga和As共面，最佳生长温度窗口很小；反射式高能电子衍射的(1×1)再构图案对生长温度和V/Ⅲ束流比不敏感，难于通过观察再构图案的变化，准确地找到最佳生长条件.作者在制备GaAs(110)量子阱过程中，观察到反射式高能电子衍射强度振荡呈现出的单双周期变化.这意味着不同工艺条件下，在 GaAs(110)衬底上量子阱有单层和双层两种生长模式.透射电子显微镜和室温光致荧光光谱测量结果表明：在双层生长模式下量子阱样品光学性能较差，而在单层生长模式下量子阱光学性能较好，但是界面会变粗糙.利用这一特点，我们采用反射式高能电子衍射强度振荡技术，找到了一种在GaAs(110)衬底上生长高质量量子阱的可行方法. 关键词： 反射高能电子衍射 量子阱 分子束外延     

Si(111)分子束外延生长时RHEED强度振荡的观察

本文报道用反射式高能电子衍射的强度振荡测量来观察Si(111)衬底上分子束外延的生长行为,观察到了双原子层的振荡模式。振荡的衰减和恢复特性不同于Si(100)衬底上的生长行为,而同GaAs分子束外延时的特性非常相似。 关键词：     

分子束外延生长Sb薄膜及其量子尺寸效应

在GaAs(001)衬底上，用分子束外延生长Sb(111)薄膜，用反射式高能电子衍射仪原位监控生长过程，用透射电子显微镜观察薄膜结构，并用van der Pauw方法测量了电阻率随生长温度的变化，观察到Sb薄膜半金属/半导体转变及其量子尺寸效应． 关键词：     

激光分子束外延BaTiO3薄膜最顶层表面原子平面与薄膜生长机理

用激光分子束外延技术在SrTiO₃(001)衬底上外延生长了高质量的BaTiO_{3< /sub>薄膜,薄膜的生长过程由反射式高能电子衍射仪(RHEED)原位实时监测,表明薄膜具有 二维层状生长模式.薄膜的晶体结构和表面形貌分别由X射线衍射和原子力显微镜表征,显示 该薄膜为完全c轴取向四方相晶体结构,其表面具有原子尺度光滑性.采用角分辨X射线光电 子谱技术(ARXPS),研究了BaTiO3薄膜表面最顶层原子种类和排列状况.结果表 明,BaTiO3 关键词： 激光分子束外延 3薄膜')" href="#">氧化物BaTiO3薄膜 最顶层表面 角分辨X射线光电子谱}     

GaP衬底上分子束外延Si时P偏析的抑制

用Si分子束外延技术在GaP(111)衬底上生长Si时,发现Si外延层表面存在P偏析,根据俄歇电子能谱(AES),反射式高能电子衍射(RHEED)在一系列不同实验条件下的结果,本文对P偏析产生的机制、外延层表面再构与P偏析之间的关系作了分析和讨论,得出偏析主要来自外延Si原子与衬底P元素之间的相互交换。在此基础上提出了一种能有效地抑制P偏析同时又改善外延层质量的新的Si/GaP(111)异质结制备方法。 关键词：     

高能电子衍射研究H钝化偏角Si衬底上Si,GexSi1-x的分子束外延生长模式

用高能电子衍射(RHEED)研究H钝化偏角Si衬底上Si,Ge_xSi_1-x材料的分子束外延(MBE)生长模式,发现经低温处理的H钝化Si衬底上要经过10nm左右的Si生长才能获得比较平整的表面.Si,Ge_xSi_1-x外延时的稳定表面均以双原子台阶为主,双原子台阶与单原子台阶并存的结构.Si双原子台阶上的Si二聚体列(dimerrow)取向垂直于台阶边缘,而Ge_xSi_1-x双原 关键词：     

用氢钝化Si(100)面抑制分子束处延界面的硼尖峰

采用一种新的简便的氢钝化方法,可以在Si(100)衬底表面获得稳定的钝化层。用俄歇电子能谱(AES),反射式高能电子衍射(RHEED),C-V和二次离子质谱(SIMS)等方法对衬底表面及其上面生长的分子束外延层进行检测,发现这种方法可以有效地防止衬底表面被碳、氧沾污,降低退火温度至少200℃,并完全消除外延层与Si(100)衬底界面处的高浓度硼尖峰。在此基础上,结合衬底表面锗束处理的实验结果,对硼尖峰的主要来源是由于硅衬底表面的氧化层这一观点提供了新的有力证据。     

高气压反射式高能电子衍射仪监控脉冲激光外延氧化物薄膜

在超高真空分子束外延（MBE）生长技术中，反射式高能电子衍射仪（RHEED）能实时显示半导体和金属外延生长过程，给出薄膜表面结构和平整度的信息，成为MBE必备的原位表面分 析仪.为了研究氧化物薄膜如高温超导（YBa₂Cu₃O₇） 、铁电薄膜（Sr_1-xBa_x TiO₃）及它们的同质和异质外延结构的生长机理，获得高质量的符合各种应用 需要的氧化 物多层薄膜结构，在常规的制备氧化 关键词： 高温超导薄膜 RHEED     

m面蓝宝石上ZnO/ZnMgO多量子阱的制备及发光特性研究

利用等离子体辅助分子束外延设备(P-MBE)在m面的蓝宝石(m-Al₂O₃)衬底上制备了ZnO/Zn_0.85Mg_0.15O多量子阱.反射式高能电子衍射谱(RHEED)图样的原位观察表明,多量子阱结构是以二维模式生长的.从光致发光谱中可以看到ZnO/Zn_0.85Mg_0.15O多量子阱在室温仍具有明显的量子限域效应.在290 K时阱宽为3 nm的ZnO/Zn_{0.85关键词： 等离子体辅助分子束外延 ZnO多量子阱 光致发光}     

Electronic structure and nematic phase transition in superconducting multiple-layer FeSe films grown by pulsed laser deposition method

We report comprehensive angle-resolved photoemission investigations on the electronic structure of single crystal multiple-layer FeSe films grown on CaF_2 substrate by pulsed laser deposition(PLD) method. Measurements on FeSe/CaF_2 samples with different superconducting transition temperatures T_c of 4 K, 9 K, and 14 K reveal electronic difference in their Fermi surface and band structure. Indication of the nematic phase transition is observed from temperature-dependent measurements of these samples; the nematic transition temperature is 140-160 K, much higher than ~90 K for the bulk FeSe. Potassium deposition is applied onto the surface of these samples; the nematic phase is suppressed by potassium deposition which introduces electrons to these FeSe films and causes a pronounced electronic structure change. We compared and discussed the electronic structure and superconductivity of the FeSe/CaF_2 films by PLD method with the FeSe/SrTiO_3 films by molecular beam epitaxy(MBE) method and bulk FeSe. The PLD-grown multilayer FeSe/CaF_2 is more hole-doped than that in MBE-grown multiple-layer FeSe films. Our results on FeSe/CaF_2 films by PLD method establish a link between bulk FeSe single crystal and FeSe/SrTiO_3 films by MBE method, and provide important information to understand superconductivity in FeSe-related systems.     

Molecular beam epitaxy of CdSe epilayers and quantum wells on ZnTe substrate

We have grown zinc-blende cadmium selenide (CdSe) epilayers on ZnTe-(0 0 1) substrate by molecular beam epitaxy (MBE). By controlling the substrate temperature and beam-equivalent pressure (BEP) ratio, of Se to Cd, we determined the most suitable growth condition based on reflection high-energy electron diffraction (RHEED) pattern. At a substrate temperature of 280 °C and a BEP ratio of 3.6, the RHEED pattern showed a V-like feature, indicating a rough surface with facets. As the substrate temperature was increased to 360 °C at the same BEP ratio, a V-like RHEED pattern moved to a clear streaky pattern. Moreover when the BEP ratio was increased to 4.8 at 360 °C of substrate temperature, a clear (2 × 1) reconstruction of the CdSe layer was observed. A CdSe/CdMgSe single quantum well structure was also grown on ZnTe-(0 0 1) substrate by MBE. The RHEED pattern showed a clear (2 × 1) surface reconstruction during the growth. By photoluminescence measurement, a good optical property of the structure was obtained.     

Oscillations in the surface structure of Sn-doped GaAs during growth by MBE

The presence of predeposited or surface-accumulated Sn during MBE growth modifies the reconstruction of the (001)GaAs surface, as observed by RHEED, at coverages as low as 0.025 monolayer. If growth is initiated on such a surface, oscillation in the intensity modulation of some of the RHEED streaks occurs, with a period equal to the monolayer deposition time of the GaAs. This oscillation decays away at a rate determined by the substrate temperature and Ga flux.     

Observation of oxygen contamination at ZnSe/GaAs interfaces using SIMS

ZnSe epilayers were grown on GaAs (1 0 0) substrates using MBE. The native contamination (oxide and carbon) was removed in situ from the substrate surfaces by conventional thermal cleaning and by exposure to atomic hydrogen. A maximum substrate temperature of 600 °C was required for the thermal cleaning process, while a substrate temperature of 450 °C was sufficient to clean the substrate using hydrogen. ZnSe epilayers were also grown on As capped GaAs epilayers, which were decapped at a maximum temperature of 350 °C. SIMS profiles showed the existence of oxygen at the interface for all of the substrate preparation methods. The oxygen surface coverage at the interface was found to be 0.03% for the atomic hydrogen cleaned substrate and 0.7% for the thermally cleaned substrate.     

Control of MBE, MOMBE and CBE growth using RHEED

This article discusses the application of reflection high energy electron diffraction (RHEED) to the control of growth by molecular beam epitaxy (MBE), metal-organic MBE (MOMBE) and chemical beam epitaxy (CBE). RHEED can be used to control the growth rate and composition for all three techniques. In addition, it has been used to control substrate temperature using changes in surface structure. It has also been used to obtain important information on the dynamics of the growth process. From this sort of data, a rather complete picture of the epitaxial process has been obtained. This has led to these UHV deposition techniques becoming the most important methods of growth for III-V compound semiconductor thin films.     

Computer modeling of morphological evolution and RHEED intensity oscillations of thin-film growth by laser molecular beam epitaxy

The morphological evolution of the unit cell by unit cell layer growth of thin films by laser molecular beam epitaxy (laser MBE) is simulated by the Monte Carlo (MC) method. As a more realistic simulation, the effect of the surface terrace on reflection high-energy electron diffraction (RHEED) intensity oscillations is considered in our model. The calculation shows that the surface terrace effect has an obvious influence on the intensity oscillation shapes. Moreover, we consider the growth units impinging on the surface batch by batch rather than one by one. It is found that the surface morphologies are different, with different numbers of units impinging by a laser pulse on the surface. Furthermore, the surface roughness increases with a decrease in substrate temperature and with an increase in the unit impinging rate (which is determined by the energy of each laser pulse). The validity of the growth model is demonstrated by comparing our MC-simulated RHEED intensity oscillations with those observed in laser MBE experiments.     

In-situ observation of MOVPE epitaxial growth

Metal organic vapour phase epitaxy (MOVPE) is nowadays one of the leading techniques for epitaxial growth. While the processes in the gas phase of MOVPE are reasonably well understood, the processes on the growing surface are not. This situation is in contrast to molecular beam epitaxy (MBE), where considerable knowledge about growth processes on the surface could be gained. The main reason is that all the UHV-based classical surface-science tools (using electrons and ions), especially reflection high-energy electron diffraction, can be applied in the vacuum-based MBE but not under the gas-phase conditions of MOVPE. This situation has changed in the last decade since optical surface-science tools have been developed. Especially, with the linear optical techniques like reflectance anisotropy spectroscopy and spectroscopic ellipsometry, there is now a quasi-standard tool at hand which allows for the study of all kinds of pregrowth and growth situations in MOVPE (in MBE of course, as well). These optical methods give, moreover, chemical information also. In this article we will describe shortly the features of these optical techniques and then concentrate on III-V-semiconductor growth. The spectral definition of surface reconstructions and time-resolved studies of phase transitions between them (adsorption/desorption kinetics of group-III and group-V elements) are discussed next. Under growth, the surfaces can be classified and defined according to their optical surface response into a pressure versus temperature phase diagram. The regions of such a phase diagram correspond to different geometrical and chemical surface structures and consequently lead to different growth modes. Finally, as an example of modern nanogrowth, monitoring of the growth of quantum-dot structures is presented. Received: 2 August 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002     

GaAs(001)表面外延生长Mn薄膜的XPS研究

利用x射线光电子能谱的深度剖面技术,对不同衬底温度下分子束外延生长的Mn薄膜及其与GaAs(001)衬底间的界面进行了元素组分和化学结合状态随深度变化的研究。实验发现衬底温度等于400K时制备的fcc-Mn/GaAs(001)体系中,fcc-Mn层与GaAs衬底之间存在一层较厚的Mn-Ga-As的缓冲层;衬底温度等于300K(室温)时制备的a-Mn/GaAs(001)体系中也存在类似的缓冲层,但它的厚度与fcc-Mn的情形相比要小得多;而当衬底温度等于450K时制备的体系在GaAs衬底之上全部是Mn-Ga     

Pyrometer unit for GaAs substrate temperature control in an MBE system

An optical pyrometer designed for precision measurement of the GaAs substrate temperature during MBE growth is considered. The pyrometer can be calibrated against a certain characteristic absolute temperature that is visually determined from a change in the RHEED pattern. This enables one to calculate the absolute temperature of the substrate with regard to its radiant emissivity and minimize the inaccuracy of radiation temperature measurement. The inaccuracy is associated with the deposition of growth products on the pyrometer window.     

Refracted X-ray Fluorescence (RXF) on Si single crystal and GaAs

The Refracted X-ray Fluorescence (RXF) method can obtain the information about surfaces and interfaces: for example, surface electron density, chemical condition and surface roughness. We evaluated surfaces and interfaces of ultrathin films by using RXF method, and we measured the average lattice constant of a ultrathin GaAs film, the top-layer of a GaAs substrate and the surface roughness of the Si substrate below a ultrathin GaAs film grown by MBE.