Mechanistic study of substrate-based galvanic replacement reactions

The sacrificial templates used in galvanic replacement reactions dictate the properties of the hollow metal nanostructures formed. Here, we demonstrate that substrate-based Au-Ag nanoshells with radically altered properties are obtained by merely coating silver templates with an ultrathin layer of gold prior to their insertion into the reaction vessel. The so-formed nanoshells exhibit much smoother surfaces, a higher degree of crystallinity and are far more robust. Dealloying the nanoshells results in the first demonstration of substrate-based nanocages. Such cages exhibit a well-defined pattern of geometric openings in directions corresponding to the {111}-facets of the starting template material. The ability to engineer the cage geometry through adjustments to the orientational relationship between the crystal structure of the starting template and that of underlying substrate is demonstrated. Together these discoveries provide the framework to advance our understanding of the mechanisms governing substrate- based galvanic replacement reactions.     

GaAs衬底上InP的直接外延生长及性能表征

用低压金属有机物气相外延(LP-MOCVD)技术,采用低温缓冲层生长法,在GaAs(100)衬底上直接生长了高质量的InP外延层.1.2 μm InP(004)面X射线衍射(XRD) ω-2θ和ω扫描半高全宽(FWHM)分别为373 arcsec和455 arcsec,在外延层中插入10周期Ga0.1In0.9P/InP应变超晶格后,其半高全宽分别下降为338 arcsec和391 arcsec.透射电子显微镜(TEM)测试显示,应变超晶格有效地抑制了失配位错穿进外延层,表明晶体质量得到了较大提高.     

基于异变缓冲层与应变层超晶格的InP/GaAs异质外延

利用低压金属有机化学气相沉积技术, 开展InP/GaAs异质外延实验。由450 ℃生长的低温GaAs层与超薄低温InP层组成双异变缓冲层, 并进一步在正常InP外延层中插入In1-xGaxP/InP(x=7.4%)应变层超晶格。在不同低温GaAs缓冲层厚度、应变层超晶格插入位置及应变层超晶格周期数等条件下, 详细比较了InP外延层(004)晶面的X射线衍射谱, 还尝试插入双应变层超晶格。实验中, 1.2 μm和2.5 μm厚InP外延层的ω扫描曲线半峰全宽仅370 arcsec和219 arcsec; 在2.5 μm厚InP层上生长了10周期In0.53Ga0.47As/InP 多量子阱, 室温PL谱峰值波长位于1625 nm, 半峰全宽为60 meV。实验结果表明, 该异质外延方案有可能成为实现InP-GaAs单片光电子集成的一种有效途径。     

Elastic strains in heteroepitaxial ZnSe1−xTex on InGaAs/InP (001)

Here we report on the elastic strains in ZnSe_1−xTe_x (x<0.9) epitaxial layers grown using photo-assisted metalorganic vapor phase epitaxy on In_0.53Ga_0.47As/InP (001) substrates. High-resolution x-ray diffraction was used to determine their composition and strain. At room temperature, we observed an apparent asymmetry in strains for tensile and compressive layers. However, when we accounted for the difference in thermal expansion between the substrate and epitaxial material, the growth temperature strain relaxation appears symmetric with respect to the sign of mismatch. The growth temperature strains are in agreement with the Matthews and Blakeslee (MB) model [J.W. Matthews and A.E. Blakeslee, J. Cryst. Growth 27, 118 (1974)] for both compressive (x>0.6) and tensile (x<0.4) layers. However, for the layers with composition in the range 0.4<x<0.6, the growth temperature strains exceed the values predicted by the MB theory. Apparently, low-mismatch layers experience a kinetic barrier to relaxation. The overall behavior can be fit by the relaxation model of Dodson and Tsao [B.W. Dodson and J.Y. Tsao, Appl. Phys. Lett. 51, 1325 (1987)] using the values Cμ²=80 s⁻¹ and γ₀=10⁻⁹.     

Interactions of dislocations and antiphase (inversion) domain boundaries in III–V/IV heteroepitaxy

The potential for interactions of misfit strain relieving dislocations with inversion-type antiphase domain boundaries is considered for III–V on group IV growth. The specific cases of GaAs grown on Si (001) and vicinal (001) substrates are examined. It is shown that threading dislocation densities for these growths should be unacceptably high due to obstruction of threading dislocation motion by the antiphase domain boundaries, even when the boundaries are eliminated shortly after the inception of GaAs layer growth. Cutting of the antiphase domain boundaries by mobile dislocations would require creation of new highenergy surface area. It is suggested that more successful routes would be growth of a strain-relieving buffer or growth on a {hhk} surface.     

Structural analysis of Ge x Si1−x /Si layers by remote plasma-enhanced chemical vapor deposition on Si (100)

In this work, remote plasma-enhanced chemical vapor deposition (RPCVD) has been used to grow Ge _x Si_1−x /Si layers on Si(100) substrates at 450° C. The RPCVD technique, unlike conventional plasma CVD, uses an Ar (or He) plasma remote from the substrate to indirectly excite the reactant gases (SiH₄ and GeH₄) and drive the chemical deposition reactions. In situ reflection high energy electron diffraction, selected area diffraction, and plan-view and cross-sectional transmission electron microscopy (XTEM) were used to confirm the single crystallinity of these heterostructures, and secondary ion mass spectroscopy was used to verify abrupt transitions in the Ge profile. XTEM shows very uniform layer thicknesses in the quantum well structures, suggesting a Frank/ van der Merwe 2-D growth mechanism. The layers were found to be devoid of extended crystal defects such as misfit dislocations, dislocation loops, and stacking faults, within the TEM detection limits (∼10⁵ dislocations/cm²). Ge _x Si_1−x /Si epitaxial films with various Ge mole fractions were grown, where the Ge contentx is linearly dependent on the GeH₄ partial pressure in the gas phase for at leastx = 0 − 0.3. The incorporation rate of Ge from the gas phase was observed to be slightly higher than that of Si (1.3:1).     

Si(100)衬底上高质量3C-SiC的改良外延生长

介绍了新近研制出的一种电阻加热式CVD/LPCVD SiC专用制备系统,并利用该系统以SiH4、C2H4和H2作为反应气体在直径为50mm的Si(100)衬底上获得了高质量的3C-SiC外延材料.用X射线衍射和Raman散射技术研究了3C-SiC外延膜的结晶质量,在80～300K的温度范围内利用Van der Pauw方法对1～3μm厚的外延膜的电学特性进行了测试,室温Hall迁移率最高达到470cm2/(V*s),载流子浓度为7.7×1017cm-3.     

金属诱导生长法在Ni硅化物上异质生长多晶GeSi薄膜

采用金属Ni诱导与超高真空化学气相沉积相结合的方法,低温下在氧化Si衬底上制备出了多晶GeSi薄膜.利用X射线衍射仪、场发射扫描电镜等对多晶GeSi薄膜的晶体质量、表面形貌进行了表征,研究了在Ni上生长多晶GeSi的生长方式及表面形貌随生长参数变化的规律.结果表明,在温度高于510℃时,Ni金属诱导作用明显;生长压强为10Pa时,多晶GeSi能够形成连续致密的薄膜,而采用先低压(0.1Pa)后高压(10Pa)的生长方式,多晶GeSi呈现分离的晶须状,晶须尺寸多在100nm以上.     

SiC／Si异质生长的研究

在半导体材料中，ＳｉＣ比Ｓｉ具有更优越的物理特性、化学特性和半导体特性，在高温、高频和功率器件制造中有十分广阔的应用前景．但是它的材料制备很困难．文中在理论分析基础上，以Ｓｉ为衬底，用常压化学气相淀积（ＡＰＣＶＤ）技术，在温度为１１００℃下，生长出ＳｉＣ多晶薄膜，样品用ＡＥＳ和Ｘ－射线衍射进行了测试和分析     

用于Si基片上外延BST薄膜的缓冲层的研究进展

由于界面之间的扩散,很难取得在Si基片上BST薄膜的外延.在这种异质结之间,稳定的缓冲层起着良好的阻挡作用以及结构上的延伸功能.综述了用于外延BST薄膜的缓冲层材料的意义和要求,及国内外通过缓冲层来控制界面以及薄膜的外延取向而获得高质量薄膜的最新研究动态,展望了今后用于外延BST薄膜的缓冲层材料发展的趋势.