激光分子束外延

介绍了激光分子束外延(Laser Molecular Beam Epitaxy)的基本原理和技术特点,评述了激光分子束外延技术在超导材料和磁性材料方面所取得的主要成就,并给出了这种技术在材料科学领域的应用前景和发展潜力.     

Si局域分子束外延技术

利用局域分子束外延技术生长了含有SiGe量子阱的岛状结构。实现了生长的岛状结构侧面不与掩模材料相接触。这种含有量子阱的岛状结构具有比相同结构量子阱强20多倍的光致发光强度。     

Recent Progress in Molecular Beam Epitaxy of HgCdTe

The recent progress in molecular beam epitaxy (MBE) growth of HgCdTe at the Epitaxy Research Center for Advanced Materials, and the National Laboratory for Infrared Physics is briefly reviewed. We have found that excellent compositional uniformity and reproducibility of HgCdTe can be achieved by the MBE technique. The results of surface morphology, dislocation density, electrical properties and focal plane array detectors are described in this paper.     

Molecular Beam Epitaxy and Properties of Cr-Doped GaSb

Molecular beam epitaxy of GaSb films, with several percents of Cr, and their characterization are reported. Their electric and magnetic properties depend on their growth temperature and Cr composition. Although magnetization measurements reveal that all the films are ferromagnetic even at room temperature, this is most probably due to the precipitation of ferromagnetic zincblende CrSb. The magnetotransport measurements show that Cr spins may couple antiferromagnetically in GaSb host matrix.     

Ferromagnetism of Mn/Ge Multilayers Grown by Molecular Beam Epitaxy

We report on novel ferromagnetic Mn/Ge multilayers for spintronics applications investigated both experimentally and theoretically. Two Mn/Ge multilayers are grown on GaAs (001) substrates by molecular beam epitaxy. The period of each multilayer consists of an Mn layer of varying thickness (0.6 and 5 Å) and a 10 Å thick Ge spacer layer. From temperature-dependent magnetization and hysteresis loop measurements, the Mn (0.6 Å)/Ge (10 Å) multilayer showed very weak ferromagnetic ordering, which is persistent up to 260 K, whereas the Mn (5 Å)/Ge (10 Å) multilayer exhibited strong ferromagnetism up to 305 K. The coercive field of the Mn (5 Å)/Ge (10 Å) multilayer was 277 Oe at 200 K. Density functional electronic band structure calculations on a number of Mn/Ge (001) multilayers determined them to be ferromagnetic, and estimates of their critical temperatures are reported.     

射频分子束外延生长氮化铝材料中缺陷的研究

采用射频分子束外延方法生长了氮化铝薄膜材料,研究了生长条件对外延层中位错和点缺陷等晶体缺陷的影响.结果表明,在富Al条件下,适当提高生长温度有利于抑制位错的产生,但同时会引入更多的氧杂质点缺陷.而对于空位点缺陷,在富Al条件下进行二维生长可同时增强Al和N原子的迁移,因此可有效地减少Al空位和N空位.但是,相比于Al空位,薄膜中的N空位更难以消除.     

ZnO薄膜的制备和结构性能分析

ZnO作为一种宽带隙半导体材料,近几年来已经成为国际上紫外半导体光电子材料和器件领域的研究热点.激光分子束外延(L-MBE)系统是获得器件级ZnO外延薄膜的先进技术之一.高质量精密ZnO陶瓷靶材对于该工艺的实施是十分关键的,本文中采用高纯原料,在洁净条件下制备了大面积、薄片型、尺寸可控的符合理想化学配比的高纯ZnO陶瓷靶材.采用所制备的靶材,利用L-MBE技术在(0001)蓝宝石基片上进行了ZnO薄膜的外延生长,在280 ℃～300 ℃低温条件下所生长的薄膜样品具有(0001)取向的纤锌矿晶体结构,薄膜光学性能良好,论文中对ZnO薄膜的低温L-MBE生长机理进行了探讨.     

MBE梯度掺杂GaAs光电阴极激活实验研究

本文首次利用分子束外延(MBE)生长了多种由体内到表面掺杂浓度由高到低的梯度掺杂反射式GaAs光电阴极材料,并进行了激活实验,结果表明,表面低掺杂浓度适中,外延层厚度2 μm～3 μm以及衬底为重掺杂p型GaAs的梯度掺杂GaAs光电阴极能够获得较高灵敏度.在优化激活工艺的条件下,梯度掺杂GaAs光电阴极获得了1798μA/lm的最高积分灵敏度,比采用同样方法制备的均匀掺杂GaAs光电阴极高30%以上.梯度掺杂GaAs光电阴极表面掺杂浓度较均匀掺杂的低,第一次给Cs时间较长,第一次Cs、O交替时要调整好Cs/O比,并在整个激活过程中保持不变.一个高量子效率梯度掺杂GaAs光电阴极的获得依赖于梯度掺杂结构和激活工艺两个方面的优化.     

Three-Chamber UHV System for Organic Molecular Beam Epitaxy

Organic Molecular Beam Epitaxy (OMBE) is a technique for growing both organic and semiconductor materials in UHV. A modular OMBE system consisting of 3 UHV chambers dedicated to specific purposes, is described. The flexibility of this system allows a wide range of optical characterisations of samples without exposure to atmosphere. The investigations are oriented on fullerenes family to create new LED device.     

Room Temperature Nanoimprint Lithography Using Molds Fabricated by Molecular Beam Epitaxy

We have demonstrated single-step room temperature nanoimprint lithography (RTNIL) using polystyrene (PS, average molecular weights ranging from 13 to 97 kg/mol) as the imprint polymer layer on a silicon substrate for imprinting rectangular line patterns with varying aspect ratios, ranging from 11 to 500 nm wide. To accomplish this demonstration, we designed and built a tool that controllably pressed a mold into a stationary imprint sample applying imprint pressures between 280 and 700 MPa. The molds used in these experiments were GaAs/AlGaAs sandwich structures fabricated by molecular beam epitaxy (MBE) that we cleaved and selectively etched afterward in order to generate 3-D grating structures with nanometer resolution on their edges. We fabricated positive and negative molds comprising single- line as well as multiline patterns with different aspect ratios and linewidths between 9 and 300 nm.     

MnGeP2 Thin Films Grown by Molecular Beam Epitaxy

Growth conditions for MnGeP₂ thin films have been investigated by using molecular beam epitaxy (MBE) method. Mn and Ge were evaporated by K-cells, and P₂ was supplied by decomposing tertialybutylphosphine (TBP). GaAs (001) and InP (001) single crystals were used as substrates. An X-ray diffraction peak, which can be assigned to (008) peak of MnGeP₂, was observed at nearly the same position as the (004) peak of GaAs. The lattice constant of the MnGeP₂ thin film was determined to be 1.13 nm assuming its crystal structure is a c-axis oriented chalcopyrite type structure. Secondary phases such as GeP, MnGe_x and MnP were observed for beam fluxes of Mn and Ge as high as 1×10^–8 Torr.     

MBE法生长ZnO纳米线阵列的结构和光学性能

在氧等离子体辅助的MBE系统中, 以1 nm厚的Au薄膜为催化剂, 基于气?液?固(VLS)机制实现了低温ZnO纳米线阵列在Si(111)衬底表面的生长. 通过场发射扫描电子显微镜(FE-SEM)可以观察到, ZnO纳米线阵列垂直生长在衬底上, 直径为20~30 nm. X射线衍射(XRD)和高分辨透射电镜(HRTEM)结果表明: ZnO纳米线为六方纤锌矿结构, 具有沿c轴方向的择优取向. 光致发光(PL)谱显示在380 nm附近有强烈ZnO本征发射峰, 475~650 nm可见光区域有较强的缺陷导致的发射峰.     

分子束外延制备稀铁磁性MnxGe1-x量子点研究进展

稀磁半导体(Diluted magnetic semiconductors,DMSs)能同时利用电子的电荷和自旋特性,从而具有了半导体材料和磁性材料的双重性能,它利用载流子及其自旋,使自旋电子器件应用于信息存储、传输、处理成为可能。因而,作为微电子产业的重要组成部分,Mn掺杂的Ge量子点(Quantum dots,QDs)稀铁磁性半导体材料由于具备与当今Si基微电子学技术的兼容性以及具有比Ⅲ-Ⅴ族DMSs更高居里温度(Curie temperature,T_C)的可能性而引起广泛关注。制备的Mn_xGe_(1-x) QDs自旋电子器件具备小尺寸、低能耗、数据处理快、集成度高、稳定性好等优异性能,对未来自旋电子器件的发展起到举足轻重的作用。虽然,由Mn掺杂的Ⅳ族Mn_xGe_(1-x) QDs DMSs材料被认为是实现室温可操控性电子自旋器件以及可控铁磁性能的理想材料候选者。但想要制备高性能、高稳定性的Mn_xGe_(1-x) QDs DMSs材料依旧面临诸多挑战。其一,虽然通过提高基质中磁性掺杂剂的浓度可以使系统获得高的T_C,但Mn掺杂剂在Ge中的极限溶解度值远低于致使系统获得高T_C的掺杂剂浓度值;其二,Ge_(1-x)Mn_x QDs中高的Mn掺杂浓度容易导致金属间析出相(如:Mn_5Ge_3和Mn_(11)Ge_8)的形成;其三,Mn掺入到Ge QDs中需要低的生长温度和低的表面扩散率,而QDs的自组装生长总是需要高的生长温度和高的表面扩散率,即实现更高的亚稳态掺杂水平可能是增强DMSs的T_C的主要限制因素;其四,铁磁性和高T_C的起源和增强机制的理论解释仍不明确,值得深入探究。因此,近年来研究者们主要从选择合适的生长参数,优化Mn_xGe_(1-x) QDs薄膜的制备工艺方面不断尝试,并取得了丰硕的成果。其一,Mn_xGe_(1-x) QDs的T_C提高至400K以上;其二,明确了金属间析出相(Mn5Ge3和Mn11Ge8)的T_C分别为296K和270K,其T_C趋于室温;其三,发现了电场控制铁磁性能和磁运输性能,首次将电场控制铁磁性温度提高至300K,并将其归结为量子限制效应;其四,由于Mn_xGe_(1-x) QDs中量子效应的存在,硼(B)的调制掺杂可以增加Mn_xGe_(1-x) QDs中的空穴浓度,从而增强其T_C。本文归纳了Mn_xGe_(1-x)稀铁磁性半导体材料的研究进展,重点归纳了分子束外延(Molecular beam epitaxy,MBE)制备稀铁磁性Mn_xGe_(1-x) QDs的研究进展。并分别介绍了各生长参数对Mn_xGe_(1-x) QDs的形态及其磁性能的影响。分析了目前研究中仍待解决的难点,展望了该材料在微电子领域的应用前景。     

激光分子束外延SrTiO3薄膜退火过程中表面扩散的研究

用激光分子束外延研究了SrTiO3同质外延时原位退火中,反射高能电子衍射(RHEED)强度的恢复--驰豫时间,导出了高真空下表面扩散的活化能为0.31 eV,与低真空下的结果相比要小许多,这反映了粒子达到基片时的能量差.对沉积不同厚度的薄膜退火研究,表明当薄膜厚度增加时,表面恢复情况减弱,而导致随后的沉积时RHEED振荡周期的改变.     

Molecular Beam Epitaxy and Electronic Structure of Atomically Thin Oxyselenide Films

Atomically thin oxychalcogenides have been attracting intensive attention for their fascinating fundamental properties and application prospects. Bi₂O₂Se, a representative of layered oxychalcogenides, has emerged as an air‐stable high‐mobility 2D semiconductor that holds great promise for next‐generation electronics. The preparation and device fabrication of high‐quality Bi₂O₂Se crystals down to a few atomic layers remains a great challenge at present. Here, molecular beam epitaxy (MBE) of atomically thin Bi₂O₂Se films down to monolayer on SrTiO₃ (001) substrate is achieved by co‐evaporating Bi and Se precursors in oxygen atmosphere. The interfacial atomic arrangements of MBE‐grown Bi₂O₂Se/SrTiO₃ are unambiguously revealed, showing an atomically sharp interface and atom‐to‐atom alignment. Importantly, the electronic band structures of one‐unit‐cell (1‐UC) thick Bi₂O₂Se films are observed by angle‐resolved photoemission spectroscopy (ARPES), showing low effective mass of ≈0.15 m₀ and bandgap of ≈0.8 eV. These results may be constructive to the synthesis of other 2D oxychalcogenides and investigation of novel physical properties.     

Ferromagnetism in (Zn,Cr)Se Layers Grown by Molecular Beam Epitaxy

Magnetization measurements of MBE grown epilayers of (Zn,Cr)Se with relatively large Cr content of 0.014 and 0.021 are presented. We evidence the presence of a strong ferromagnetic coupling between Cr ions, but also suggest a significant clustering due to a pronounced superparamagnetic behavior found in the layers. We estimate the intraparticle Curie temperature to be about 100 K, which combined with other arguments appears to indicate that some magnetic properties of Cr-rich layers might be dominated by the presence of small grains of A^II–Cr₂–B₄ ^VI spinels.     

四步法制备高质量硅基砷化镓薄膜

为了提高在硅基上外延砷化镓薄膜的质量和实验的可重复性, 我们提出了一种叫做四步生长法的新方法, 该方法是通过在低温成核层和高温外延层中间先后插入低温缓冲层和高温缓冲层实现的。通过此方法, 可以制备出表面具有单畴结构、在强白光下依然光亮如镜、粗糙度低且缺陷少的高质量砷化镓薄膜, 而且此方法的重复性很好。即便没有任何生长后的退火处理, 外延出的1 μm厚砷化镓薄膜在5 μm×5 μm扫描区域内的表面粗糙度只有2.1 nm, 且由X射线双晶衍射测试出的砷化镓(004)峰的半高宽只有210.6 arcsec。     

Selective-Area Growth of GaN Nanowires on Patterned SiOx/Si Substrates by Molecular Beam Epitaxy

Technical Physics Letters - We demonstrate the possibility of selective-area growth of ordered arrays of GaN nanowires by molecular beam epitaxy on SiOx/Si substrates patterned by photolithography...