超高真空CVD生长的Si1—xGex合金组分变化与表面偏析现象

系统分析了利用超高真空ＣＶＤ技术在Ｓｉ衬底上外延Ｓｉ－ｘＧｅｘ合金的体内组分分布情况和Ｇｅ的表面偏析现象。用ＳＩＭＳ对Ｓｉ和Ｇｅ的组分作了深度剖析。在生长过程中,组分均匀,在表面Ｇｅ浓度减小,Ｓｉ浓度没有明显变化。在不经ＨＦ酸清洗和在ＨＦ酸中去掉表面自然氧化层的两种情况下,用ＸＰＳ分别对外延层表面进行了定量分析,得到Ｇｅ的表面偏析与表面自然氧化相关的结论。     

改善UHV／CVD外延生长环境提高GeSi／Si材料性能有效方法

本阐述了应用国产ＵＨＶ／ＣＶＤ设备处延生长的ＧｅＳｉ／Ｓｉ材料碳、氧含同的原因,定量地分析了有害残余气体的成分,提出了改善处延生长环境提高ＧｅＳｉ／Ｓｉ材料性能的有效方法。     

分子束外延生长GaAs中δ掺杂研究

利用二次离子质谱（ＳＩＭＳ）和电化学剖面Ｃ－Ｖ方法研究了生长温度对ＧａＡｓ中理想Ｓｉδ掺杂的结构的偏离和掺杂原子电微活效率的影响。实验发现，外延生长Ｓｉδ掺杂，ＧａＡｓ时，随着生长温度的升高，Ｓｉ掺杂分布ＳＩＭＳ峰非对称展宽。表面分凝作用加强，但不影响Ｓｉ原子扩散。另外，Ｓｉ施主电激活效率随着生长温度的提高而增大。     

束流密度对Ge/Si量子点溅射生长的影响

采用离子束溅射技术在Si基底上自组织生长了一系列Ge量子点样品,研究了束流密度对Ge/Si量子点的尺寸分布和形貌演变的影响。原子力显微镜测试结果表明,随着束流密度的增加,量子点的面密度持续增大,其尺寸不断减小,量子点的形貌由圆顶形转变为过渡圆顶形。计算直径标准偏差的结果表明,当束流密度为0.86mA/cm2时,量子点的尺寸均匀性最佳。束流密度与沉积速率成正比,影响着表面吸附原子与其它原子相遇而形成晶核的能力。     

锗硅碳合金中碳的应变缓解效应研究

ＳｉＧｅＣ三元合金成为近年来人们研究的热点之一。处于替代位置的碳可以缓解ＳｉＧｅ合金的应变,同时调节其能带,在能带工程上提供了更大的灵活性。本文利用ＵＨＶ／ＣＶＤ技术生长了掺碳达２．２％的锗硅碳合金,获得了良好的外延层质量,并对碳的应变缓解效应进行了研究。     

GexSi1-x材料生长的改善

利用超高真空化学相淀积（ＵＨＶ／ＣＶＤ）系统在６５０℃生长出表面光亮的ＧｅＳｉ单晶。在１２００Ｌ／ｍｉｎ分子泵与前级机械泵间串接４５０Ｌ／ｍｉｎ分子泵,改善了生长环境。串接分子泵后生长的样品的Ｘ射线双晶衍射分析表明,外延层衍射峰半宽仅为１９８ａｒｃｓｅｃ,且出现了Ｐｅｎｄｅｌｌｏｓｕｎｇ干涉条纹,说明外延层结晶质量很好。     

含活性基团硅氮烷先驱体的裂解

用ＴＧ－ＧＣ，ＩＲ，元素分析，ＸＲＤ研究ＭｅＳｉＨＣｌ２与ＭｅＳｉＶｉ（Ｖｉ：－ＣＨ＝ＣＨ２）Ｃｌ２共氨解产物的裂解过程。     

超高真空化学气相淀积自组织生长锗量子点

采用超高真空化学气相淀积系统制备了小尺寸、高密度、纵向自对准的Ge量子点．通过TEM和AFM对埋层和上层量子点的形貌和尺寸分布进行了研究，对生长的温度和时间进行了优化．采用硼预淀积的方法得到了尺寸分布小于3％的均匀的圆顶形Ge量子点．采用低温光荧光测量了多层量子点的光学特性．在10K的PL谱可以观察到明显的蓝移现象，表明量子点中较强的量子限制效应．量子点非声子峰的半高宽约为46meV，表明采用UHV／CVD工艺生长的多层量子点具有较窄的尺寸分布．     

掺Si对MOCVD生长的GaN单晶膜的黄带发射及生长速率的影响

对ＭＯＣＶＤ生长ＧａＮ：Ｓｉ薄膜进行了研究,研究表明随ＳｉＨ４／ＴＭＧａ流量比增大,ＧａＮ：Ｓｉ单晶膜的电子浓度增大,迁移率下降,Ｘ射线双晶衍射峰半高宽增加,同时这发射强度得到了大大的提高,并报导了随ＳｉＨ４／ＴＭＧａ流量比增大,ＧａＮ：Ｓｉ的生长速率降低的现象,研究结果还表明,预反应对ＧａＮ：Ｓｉ单晶膜黄带发射影响很大,预反应的减小可以使黄带受到抑制。     

（BiAl）YIG薄膜的生长感生磁各向异性

从理论和实验上分析了Ｆｅ＾３＋和Ｆｅ＾２＋对（ＢｉＡ）ＹＩＧ薄膜的生长感各向异性的贡献，掺Ｂｉ导致的生长磁感生各向异性，来源于Ｅｉ＾３＋改变了Ｆｅ＾３＋的零场劈裂，其大小取决于Ｂｉ＾３＋含量及在十二面体位的择优分布，高价离子和氧空位形成的Ｆｅ＾２＋在八面体位的择优分布，对生长感生磁各向异性也有贡献。     

Influencing factors on the size uniformity of self-assembled SiGe quantum rings grown by molecular beam epitaxy

The size uniformity of self-assembled SiGe quantum rings, which are formed by capping SiGe quantum dots with a thin Si layer, is found to be greatly influenced by the growth temperature and the areal density of SiGe quantum dots. Higher growth temperature benefits the size uniformity of quantum dots, but results in low Ge concentration as well as asymmetric Ge distribution in the dots, which induces the subsequently formed quantum rings to be asymmetric in shape or even broken somewhere in the ridge of rings. Low growth temperature degrades the size uniformity of quantum dots, and thus that of quantum rings. A high areal density results in the expansion and coalescence of neighboring quantum dots to form a chain, rather than quantum rings. Uniform quantum rings with a size dispersion of 4.6% and an areal density of 7.8×10(8) cm(-2) are obtained at the optimized growth temperature of 640°C.     

Influence of Si interdiffusion on carbon-induced growth of Ge quantum dots: a strategy for tuning island density

We have studied the epitaxial growth of self-assembled Ge quantum dots when a submonolayer of carbon is deposited on a Ge wetting layer (WL) prior to the growth of the dots. Using atomic-force microscopy combined with optical techniques like Raman and ellipsometry, we performed a systematic study of the role played by thermally activated Si interdiffusion on dot density, composition and morphology, by changing only the growth temperature T(WL) of the WL. Strikingly, we observe that higher dot densities and a narrower size distribution are achieved by increasing the deposition temperature T(WL), i.e.?by enhancing Si interdiffusion from the substrate. We suggest a two-stage growth procedure for fine tuning of dot topography (density, shape and size) useful for possible optoelectronic applications.     

快速热退火对多层Ge量子点晶体质量的影响

使用超高真空化学气相淀积(UHV/CVD)设备在Si衬底上生长多层Ge量子点,用双晶X射线衍射(DCXRD)、拉曼光谱(Raman)等手段表征在不同条件下快速热退火的Ge量子点材料的组分、应力等特性,研究了快速热退火对多层Ge量子点晶体质量的影响.结果表明:随着退火温度的升高,量子点中Ge的组分下降,量子点应变的弛豫程...     

Sb mediated formation of Ge/Si quantum dots: Growth and properties

The phenomenon of surfactant (Sb) mediated formation of Ge/Si(100) islands (quantum dots) by means of molecular beam epitaxy is discussed. The limited diffusivity of Si and Ge adatoms caused by the Sb layer leads to a reduction of the size of Ge islands, the increase in the island density, and the sharpening of the interfaces of Ge islands. Thereby, a thin Sb layer is considered to be a powerful tool that provides more freedom in designing Ge quantum dot features. Ge quantum dots, grown via a thin Sb layer and embedded coherently in a Si p-n junction, are revealed to be the origin of the intense photo- and electroluminescence in the spectral range of about 1.5 μm at room temperature.     

500℃下利用UHV/CVD在Si衬底上直接生长近平面Si0.5Ge0.5层

利用UHV/CVD系统,在一个相对较低的温度500℃下,研究了Si1-xGex层中的Ge含量与生长条件之间的关系,此时的Si1-xGex层处于一种亚稳的状态.并直接在Si衬底上生长制备了10个周期的3.0 nm-Si0.5Ge0.5/3.4 nm-Si多量子阱.拉曼谱、高分辨显微电镜和光荧光谱对其结构和光学性能进行的表征表明这种相对较厚的Si0.5Ge0.5/Si多量子阱结构基本上仍是近平面生长的,内部没有位错,其在电学和光学器件上具有潜在的应用.     

InGaAs quantum dots grown by molecular beam epitaxy for light emission on Si substrates

The aim of this study is to achieve homogeneous, high density and dislocation free InGaAs quantum dots grown by molecular beam epitaxy for light emission on silicon substrates. This work is part of a project which aims at overcoming the severe limitation suffered by silicon regarding its optoelectronic applications, especially efficient light emission device. For this study, one of the key points is to overcome the expected type II InGaAs/Si interface by inserting the InGaAs quantum dots inside a thin silicon quantum well in SiO2 fabricated on a SOI substrate. Confinement effects of the Si/SiO2 quantum well are expected to heighten the indirect silicon bandgap and then give rise to a type I interface with the InGaAs quantum dots. Band structure and optical properties are modeled within the tight binding approximation: direct energy bandgap is demonstrated in SiO2/Si/InAs/Si/SiO2 heterostructures for very thin Si layers and absorption coefficient is calculated. Thinned SOI substrates are successfully prepared using successive etching process resulting in a 2 nm-thick Si layer on top of silica. Another key point to get light emission from InGaAs quantum dots is to avoid any dislocations or defects in the quantum dots. We investigate the quantum dot size distribution, density and structural quality at different V/III beam equivalent pressure ratios, different growth temperatures and as a function of the amount of deposited material. This study was performed for InGaAs quantum dots grown on Si(001) substrates. The capping of InGaAs quantum dots by a silicon epilayer is performed in order to get efficient photoluminescence emission from quantum dots. Scanning transmission electronic microscopy images are used to study the structural quality of the quantum dots. Dislocation free In50Ga50As QDs are successfully obtained on a (001) silicon substrate. The analysis of QDs capped with silicon by Rutherford Backscattering Spectrometry in a channeling geometry is also presented.     

Real-time studies of Ge growth on nanostructured Si substrates

Nanostructured substrates are an interesting path towards the production of quantum dots devoted to microelectronic applications. In this work we report results on the effects of different nanopatterning methods to obtain lateral ordering of Ge islands grown on Si. By using Scanning Tunneling Microscopy we have studied in real-time the wetting layer growth and islands formation on nanopatterned Si substrates at 500 °C. We compare results obtained on Si substrates nanopatterned by using two different techniques: STM lithography and natural patterning induced by surface instabilities such as step bunching. Different issues on both cases have been addressed: substrate preparation, Ge dots placement and growth mode. We have observed that, on Si(001), the Ge islands nucleate near the holes and on Si(111) step bunching can guide the growth of aligned rows of islands.     

In situ RHEED control of self-organized Ge quantum dots

In situ registration of high-energy electron diffraction patterns was used for constructing the diagram of structural and morphological states of the Ge film on the Si(100) surface. The following regions identified in the diagram: two-dimensional (2D)-growth, ‘hut’- and ‘dome’-clusters, ‘dome’-clusters with misfit dislocations at the interface. Variations in the lattice constants of the Ge film during the MBE growth on the Si(100) surface were determined. An increase in the lattice constant at the (100) surface was attributed to the elastic deformation at the stage of 2D growth and formation of ‘hut’-clusters and to the plastic relaxation for the ‘dome’-clusters. As a result, epitaxial silicon structures with germanium quantum dots of 15 nm base size at the density of 3×10¹¹ cm⁻² were synthesized. The total electron structure of the hole spectrum of Ge quantum dots in Si was established.