用RHEED强度振荡锁相外延控制Ge/Si超晶格的生长

观察了Ge,Ge/Si交替外延时的反射式高能电子衍射(RHEED)强度振荡现象,并由此研究了Si(100)和Si(111)衬底上分子束外延Ge,Ge/Si超薄叠层的生长行为和生长特性。利用RHEED强度振荡,锁相控制生长了Ge(2ML)/Si(2ML),Ge(4ML)/Si(4ML)超薄超晶格。 关键词：     

Si衬底上分子束外延Ge,Si时的反射式高能电子衍射强度振荡观察

本文观察了在Si(100)和Si(111)衬底上分子束外延Si,Ge时的反射式高能电子衍射(RHEED)强度振荡现象。其振荡特性表明,外延一定厚度的缓冲层可以改善表面的平整性,较慢的生长速率或中断生长一段时间有利于外延膜晶体质量的提高。Si(100)上外延Si或Ge时,沿[100]和[110]方位观测到的振荡特性均为单原子模式,起因于表面存在双畴(2×1)再构;而Si(111)上外延Ge时,[112]方位观测到的振荡为双原子层模式,但在[110]方位观察到不均匀周期的强度振荡行为。两种衬底上保持RHEED     

湿法刻蚀对Si基片孔点阵及ZnO外延薄膜周期形貌的影响

利用射频等离子体辅助分子束外延法,在刻有周期性孔点阵结构的Si衬底上生长了ZnO二维周期结构薄膜,系统研究了湿法化学刻蚀对孔形点阵Si(100),Si(111)基片表面形貌的影响,以及两种初底上ZnO外延薄膜的结晶质量与周期形貌的差异.X射线衍射及扫描电子显微测试结果表明：Si (111)衬底上生长出的ZnO二维周期结构薄膜具有较好的结晶质量与较好的周期性表面形貌.该研究结果为二维周期结构的制备提供了一种新颖的方法. 关键词： ZnO 分子束外延 Si 湿法刻蚀     

Si(111)分子束外延的生长动力学过程研究

本文用反射式高能电子衍射(RHEED)强度振荡研究了不同生长温度下Si(111)分子束外延的生长动力学过程,生长温度高于520℃(生长速率约0.15?/S)时,Si(111)外延为“台阶流”生长模式,生长温度低于475℃时,外延为“二维成核”双原子层生长模式,在较低温,甚至室温时,其外延仍为双原子层模式,但是镜向弹性散射束振荡和非弹性散射束振荡的叠加会造成RHEED强度在生长的最初阶段出现“类单原子层”模式的振荡特性。 关键词：     

低温Si(111)-7×7表面Pb纳米薄膜的生长模式与沉积速率的依赖关系

本文利用超高真空腔室中的分子束外延手段在低温Si(111)衬底上外延生长Pb纳米薄膜.分析了不同沉积速率下Pb纳米薄膜的尺寸、台阶高度等参数变化情况,研究了不同条件下薄膜的形貌特性,并据此提出Pb纳米薄膜在不同沉积速率下的生长模式差异.     

(113)面硅衬底上自组织生长的GeSi量子点及其光荧光

用透射电子显微镜观察了Si(113)衬底上由固态源分子束外延生长的自组织量子点的形貌,测量了其原生及退火后低温下的光荧光谱.对所得结果进行了分析. 关键词：     

Si1－xGex/Si量子阱发光材料的分子束外延生长及其结构研究

采用固源Si分子束外延,在较高的生长温度于Si(100)衬底上制备出Si1－xGex/Si量子阱发光材料。发光样品的质量和特性通过卢瑟福背散射、X射线双晶衍射及光致发光评估。背散射实验中观察到应变超晶格的反常沟道效应;X射线分析表明材料的生长是共度的、无应力释放的,结晶完整性好。低温光致发光主要是外延合金量子阱中带边激子的无声发射和横光学声子参与的激子复合。并讨论了生长温度对量于阱发光的影响。     

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：     

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：     

Si(100)表面Se薄膜生长及其在Ti/Si欧姆接触中的应用

本文采用分子束外延(MBE)系统在Si(100)表面淀积Se薄膜. 通过控制衬底和固态Se束源炉的温度,实现了Se材料在Si(100)表面上的自限制超薄薄膜生长;在Se超薄层钝化的Si(100)表面上制备的Ti金属电极具有低的欧姆接触电阻特性,且热稳定性温度提升至400 ℃. 关键词： 硒 钝化 欧姆接触 热稳定性     

电子衍射条件对Si(111)外延时反射式高能电子衍射强度振荡的影响

本文研究了不同电子衍射条件对Si(111)外延时的反射式高能电子衍射(RHEED)强度振荡的影响,在保持生长条件不变的情况下,沿[112]方位观测时,不同入射角下其强度振荡的相位和初始瞬态响应变化很大,甚至会发生180°相位变化,而在[011]方位观测时,其相位的变化不明显,结合Si(111)面的RHEED强度摇摆曲线测量结果,表明这种与电子衍射条件有关的振荡特性变化,实际上反映了由电子多重散射机理引起的RHEED强度振荡两种情形,对RHEED强度的初始瞬态响应机理也作了探讨。 关键词：     

Growth dynamics studied by RHEED during Si/Ge epitaxy from gaseous hydrides

Si and Ge epitaxial growth from disilane and germane in a gas-source molecular beam epitaxy (GSMBE) system is followed in situ by reflection high-energy electron diffraction (RHEED) intensity oscillations. During Ge homoepitaxy, the growth rate on a Ge(100) substrate is found to be limited by surface hydrogen desorption below 350°C and by hydride adsorption above this temperature. Ge heteroepitaxy on Si results in incomplete layer growth leaving exposed Si at the surface during the initial stages of growth. Therefore, a gradual change in the observed Si surface concentration is seen as growth proceeds. Si heteroepitaxy on Ge follows the Volmer-Weber growth mode and proceeds via island formation. This, combined with Ge surface segregation, results in a slow decrease of the Ge surface population at the growth front. During heteroepitaxial growth, hydride reaction rates differ on Si and Ge surfaces, and therefore a changing concentration of the surface species is manifest as a gradual change in the observed oscillation frequency. This effect, observed during the early stages of growth, shows strong temperature dependence, consistent with previous observations on SiGe alloys. Following several layers of growth, however, the surfaces become rough. The influence of this roughness on the oscillation frequency is also discussed.     

Thermodynamic evolution of antiphase boundaries in GaP/Si epilayers evidenced by advanced X-ray scattering

We have investigated quantitatively anti-phase domains (APD) structural properties in 20 nm GaP/Si epilayers grown by molecular beam epitaxy, using fast, robust and non-destructive analysis methods. These analyses, including atomic force microscopy and X-ray diffraction, are applied to samples grown by various molecular beam epitaxy growth modes. Roughness, lateral crystallite size of the epilayer, ratio of antiphase domains and their relationship are discussed. It is shown that both these analysis methods are useful to clarify the physical mechanisms occurring during the heterogeneous growth. Low temperature migration enhanced epitaxy is found to guarantee smoother surface than conventional molecular beam epitaxy. Effect of annealing temperature on antiphase boundaries (APBs) thermodynamics is discussed. The modification of the thermodynamic equilibrium through a thermal activation of APBs motion is expected to play an important role in the dynamic evolution of surfaces during thermal annealing and growth.     

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     

LASER MOLECULAR BEAM EPITAXY SYSTEM AND ITS KEY TECHNOLOGIES

The laser molecular beam epitaxy system and its key technologies have been successfully developed in China. Atomically regulated unit-cell by unit-cell homoepitaxial SrTiO₃ (STO) and heteroepitaxial BaTiO₃ (BTO) films and STO/BTO superlattices were fabricated on STO (100) substrates by the laser molecular beam epitaxy. The fine streak patterns and more than 1000 cycles of undamping intensity oscillation were obtained by using in-situ reflection high-energy electron diffraction. The surfaces of films are atomically smooth.     

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.     

Quantum confined luminescence in Si/SiO2 superlattices

Amorphous Si/SiO₂ superlattices with periodicities between 2 and 5 nm have now been grown on (1 00) Si wafers by several different techniques: molecular beam epitaxy, magnetron sputtering, and plasma enhanced chemical vapor deposition (PECVD). With the first two methods little or no hydrogen is incorporated during growth and visible photo-luminescence (PL) is obtained at wavelengths from 520 to 800 nm. The shift in the PL peak position with Si layer thickness is consistent with quantum confined band-to-band recombination. Annealing the sputtered superlattices at temperatures up to 1100°C results in a very bright red PL that is similar in intensity to that observed in porous Si samples. For large numbers of periods (e.g., 425) the PL is strongly modulated in intensity owing to optical interference within the superlattice. Similar quantum confined, but defect induced, PL is also observed in the PECVD grown superlattices, where the amorphous Si layers are heavily hydrogenated.     

Ge/Si(111)与Si/Ge(111)体系的生长特性与表面再构研究

本文利用RHEED和AES对Ge/Si(111)和Si/Ge(111)体系的生长特性与表面再构进行了研究。由此提出了其生长模式,并讨论了应力对生长特性、界面特性和表面再构的作用。