Sb-modified growth of stacked Ge/Si(100) quantum dots

We report on the Sb induced modifications of the morphology of self assembled Ge/Si(100) quantum dot stacks in a Si matrix grown by a molecular beam epitaxy. It is shown that the size of the quantum dots in the stack and the Si spacer layer uniformity inside the stack are regulated by the amount of deposited Sb. We consider the thin Sb layer at the Ge/Si growth interface as a factor limiting the surface migration of Si and Ge ad-atoms. The surface diffusion coefficients of Si ad-atom on uncovered pyramid shaped Ge island and on a Ge island covered by a single monolayer of Sb are estimated to be 2.4 μm²s⁻¹ and 2.3 × 10⁻⁴ μm²s⁻¹ at a temperature of 600 °C, correspondingly. Based on this remarkable reduction of surface diffusion the morphology of the surface can be preserved when the growth is continued after the single monolayer of Sb is at the surface.     

硅、锗材料在Si(100)表面的生长研究

利用扫描隧道显微镜和超高真空实验装置系统进行了Si(10 0 )表面生长Si,Ge的实验研究。分析了所生成表面的形貌、结构等物理性质。研究表明 :Si在Si(10 0 )表面的同质生长可以形成纳米结构薄膜。Ge在Si(10 0 )表面生长形成规则的三维小岛。而在Si/Ge/Si(10 0 )多层膜上生长则形成大小二种三维岛。研究表明大岛具有Ge/Si/Ge的壳层结构     

Boron ions B interaction with Si(100) and Ge(100) surfaces

The goal of this work is simulation of possible structures, formed by boron ions (B⁺) during adsorption on Si(100) and Ge(100) surfaces. Calculations were carried out using a semi-empirical method, known as the Modified Neglect of Differential Overlap method (MNDO). The surface was simulated using of Si₄₉(Ge₄₉) and Si₆₃(Ge₆₃) clusters. Results of quantum-chemical calculations the boron ion (B⁺) interaction with Si(100) − 2 × 1 and Ge(100) − 2 × 1 surfaces are presented and show adsorption barriers for boron ions and migration barriers of adsorbed boron ion (during migration along surface dimer row and along surface dimer).     

Peculiarities in the morphology of ge island array on Si(100) at a subcritical thickness of the deposited Ge layer

Experiments revealed the formation of Ge islands on a Si(100) surface at an effective thickness of the deposited germanium layer below the critical value for the transition from two-to three-dimensional growth. The number density of Ge islands in the array was 3×10⁸ cm^?2. The results are interpreted within the framework of a kinetic model of the island formation in heteroepitaxial systems with lattice mismatch.     

溅射气压对Ge/Si纳米点表面形貌的影响

利用磁控溅射技术在Si(100)衬底上直接外延生长一系列不同压强下的Ge纳米点样品,并利用AFM、Raman和XRF对Ge纳米点样品形貌和结构进行了研究。结果表明Ge薄膜表面粗糙度在某一临界压强下发生突变,高能粒子热化的临界值与这种转变密切相联;分析讨论了Ge岛在不同溅射气压下的生长过程,在一定范围随着压强的增大会显示典型生长阶段的特征。     

On morphology and strain field of Ge/Si(001) Islands according to TEM phase imaging method

The mechanism driving Germanium islands nucleation and self-assembly is an important effect for opto-electronic applications, still not fully understood. We demonstrate that the new transmission electron microscopy phase imaging method provides insights on the distribution of strain and composition fields in and around the islands on rather large areas. The method consists of retrieving the phase from a focus series of plane view images. The phase image is representative of morphology, composition and strain. The results show that whatever the islands size and shape is, a maximum compressive strain is obtained at the apex of the islands compensated by a maximum tensile strain in the substrate close to the islands perimeter. The maximum compressive strain is associated to a larger Ge concentration. The distribution of tensile strain varies with the shape of the islands: for square base pyramidal "hut" islands, a maximum tensile strain is obtained at the four corners of the pyramid base and for "dome" islands, the tensile strain is less pronounced and affects almost the whole island perimeter. These results are consistent with the higher strain relaxation level of "dome" islands in comparison to those of "hut" islands.     

Ge组分渐变的Si1-x-yGexCy薄膜的制备

用化学气相淀积方法在Si（100）衬底上外延生长了Ge组分最高约0．40的组分渐变的Si1-x-yGexCy合金薄膜,研究了生长温度等工艺参数的影响．结果表明,生长温度和C2H4分压的提高均导致薄膜中碳组分的增加和合金薄膜晶格常数的减小,这表明外延薄膜中的C主要以替位式存在．C掺入量的变化可有效地调节薄膜的禁带宽度,而提高生长温度有助于改善Si1-x-yGexCy薄膜的的晶体质量．组分渐变的Si1-x-yGexCy合金薄膜包括由因衬底中Si原子扩散至表面与GeH4．C2H4反应而生成的Ni1-x-yGexCy外延层和由Ni1-x-yGexCy外延层中Ge原子向衬底方向扩散而形成的Ni1-xGex层．     

Effect of the growth rate on the morphology and structural properties of hut-shaped Ge islands in Si(001)

The effect of Ge deposition rate on the morphology and structural properties of self-assembled Ge/Si(001) islands was studied. Ge/Si(001) layers were grown by solid-source molecular-beam epitaxy at 500?°C. We adjusted the Ge coverage, 6?monolayers (ML), and varied the Ge growth rate by a factor of 100, R = 0.02-2?ML?s(-1), to produce films consisting of hut-shaped Ge islands. The samples were characterized by scanning tunnelling microscopy, Raman spectroscopy, and Rutherford backscattering measurements. The mean lateral size of Ge nanoclusters decreases from 14.1?nm at R = 0.02?ML?s(-1) to 9.8?nm at R = 2?ML?s(-1). The normalized width of the size distribution shows non-monotonic behaviour as a function of R and has a minimum value of 19% at R = 2?ML?s(-1). Ge nanoclusters fabricated at the highest deposition rate demonstrate the best structural quality and the highest Ge content (～0.9).     

Diffusion in Si(x)Ge(1-x)/Si nanowire heterostructures

Si0.48Ge0.52/Si tip/nanowire heterostructures were grown by pulsed laser vaporization (PLV) at a growth temperature of 1100 degrees C. Ge diffusion in [111]-growth Si nanowires was studied for different post-synthesis annealing temperatures from 200 degrees C to 800 degrees C. Ge composition profiles were quantified by energy-dispersive X-ray spectroscopy in a transmission electron microscope. The compositional profiles were modeled by a limited-source diffusion model to extract temperature-dependent diffusion coefficients. The Ge diffusion coefficients followed an Arrhenius relationship with an activation energy of 0.622 +/- 0.050 eV. This rather low activation energy barrier is similar to the previously reported activation energy barrier of 0.67 eV for Ge surface diffusion on Si, suggesting that surface diffusion may dominate in nanowires at this length scale.     

Electrical Resistance of W/Si–Ge (0–75 wt % Ge) Contacts

The electrical resistance of the contact between tungsten and silicon–germanium alloys of different compositions was measured as a function of temperature. The results indicate that the room-temperature contact resistance increases with increasing Ge content, annealing temperature, and annealing time. With increasing measuring temperature, the contact resistance drops to a level of the experimental error. Annealing at 1070 K tends to break down both W/p-Si–Ge and W/n-Si–Ge contacts.     

Composition and atomic ordering of Ge/Si(001) wetting layers

A combination of X-ray diffraction with anomalous X-ray scattering at the Ge K edge and specular reflectivity measurements is used to reveal both composition and atomic ordering in Ge:Si wetting layers. By comparing the intensity distribution close to the (400) and (200) surface reflections we show that the Ge wetting layer is composed of a SiGe alloy which exhibits atomic ordering. Due to the Si interdiffusion the wetting layer thickness is larger than the nominal 3 ML Ge deposition. The chemical depth distribution is obtained from X-ray reflectivity measurements and confirms the enhanced Ge interdiffusion. These phenomena evidence the crucial interplay between surface kinetics and intermixing in SiGe thin films and nanostructures on Si(001) substrates.     

Ge oxidation in the remaining cores of Si(1-x)Ge(x) nanowires after prolonged oxidation

For this investigation of the Ge behavior of condensed Si(1-y)Ge(y) (y > x) cores during the oxidation of Si(1-x)Ge(x) nanowires, Si(1-x)Ge(x) nanowires were grown in a tube furnace by the vapor-liquid-solid method and thermally oxidized. The test results were characterized using several techniques of transmission electron microscopy. The two types of Ge condensation are related to the diameter and Ge content of the nanowires. The consumption of Si atoms in prolonged oxidation caused the condensed SiGe cores to become Ge-only cores; and the continuous oxidation resulted in the oxidation of the Ge cores. The oxidation of Ge atoms was confirmed by scanning transmission electron microscopy.     

Island formation in Ge/Si epitaxy

We review current understanding of the island formation process, and outline some of the remaining problems. The initial island formation is coherent, with islands stabilised by the elastic relaxation associated with deformation of the substrate. We use finite element analysis to demonstrate the degree of relaxation associated with these deformations. The islands then relax further by introduction of dislocations. The first dislocations introduced in the large coherent islands are shown to be inclined burgers vectors (about 60°) adopting a nearly semicircular path around the island perimeter. The outstanding anomaly in Ge/Si growth is the temperature dependence of islanding, with slower relaxation rates and greater metastability associated with higher temperatures. We describe various possible explanations for this problem.     

SiO2/Si(111)表面Ge量子点的生长研究

Si衬底用化学方法清洗后,表面大约残余1.0 nm厚SiO2薄膜.利用原子力显微镜(AFM)和反射高能电子衍射(RHEED)来研究温度和Ge蒸发厚度对在SiO2薄膜表面生长的Ge量子点的影响.实验结果表明,当衬底温度超过500 ℃时,SiO2开始与Ge原子发生化学反应,并形成与Si(111)表面直接外延的Ge量子点.在650 ℃时,只有Ge的厚度达到0.5nm时,Ge量子点才开始形成.     

Effect of the nature of the precursor on the morphology of MoO3 thin films spin-coated on Si (100)

Thin films of α-MoO₃ were efficiently deposited on Si (100) by spin-coating of various precursor solutions i.e. ammonium heptamolybdate (HMA), citrate (CIT) and oxalate (OXA) complexes of Mo⁶⁺, and peroxo-polymolybdic (PER) solutions. The effect of the nature and concentration of the precursor and of the spin-coating rate were studied by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The nature of the precursor used for the deposition influences the morphology of the crystals. For films obtained from CIT precursor solutions, an anisotropic morphology of MoO₃ crystals with predominant basal faces is obtained, while MoO₃ crystals spin-coated from PER precursor solutions possess a more isotropic morphology. Films deposition from OXA and HMA precursors possess an intermediate morphology. Homogeneity and thickness of the films can be adjusted by tuning the concentration of the precursor solution and the spin-coating rate. Whatever the precursor used, the larger the crystals formed, the more developed were the basal faces obtained.     

重构表面上Si薄膜生长的模拟研究

建立了Si(100)-(2×1)表面上Si薄膜生长的Kinetic Monte Carlo(KMC)模型,并对薄膜生长的初始阶段进行了研究.结果表明:在一定的入射率下存在一最佳成岛温度,该温度随入射率的增大而升高,并满足函数关系T=T0 bln(F c).     

Confinement of one-dimensional electrons in dimer row segments at Ge/Si(001) surfaces

During the initial growth, Si(001) surfaces were covered by thin Ge wetting layers. At the wetting layer surfaces, Ge atoms were reconstructed into dimers, which were aligned along the [110] direction to form one-dimensional (1D) ‘dimer rows’. In addition, the dimer rows were partitioned by dimer vacancy lines at the Ge/Si(001) surfaces. As a result, the surfaces were covered spontaneously by an array of 1D dimer row segments. Scanning tunneling microscope images demonstrated that the 1D free-electrons in the dimer rows are confined in each segment and form an ultra-high density array of 1D quantum wells at the surfaces.     

离子注入诱导硅材料发光的研究进展

阐述了采用离子注入技术在硅晶体(Si)中形成缺陷的发光机制,综述了离子注入诱导硅材料发光的研究进展,包括稀土离子掺入硅晶体形成稀土杂质中心发光,Ⅳ族元素C、Ge离子注入Si/SiO2形成等离子缺陷中心发光,以及B、S、P等常规离子注入硅晶体的缺陷发光,其中重点介绍了Si离子自注入诱导硅材料发光的研究现状,最后展望了硅基材料发光的未来发展。     

Ge/Si量子点生长的研究进展

回顾了近年来在Ge/Si量子点生长方面的研究进展.主要讨论了为了提高量子点空间分布有序性、增大量子点的密度、减小量子点的尺寸及改善其分布均匀性而采取的各种方法,如图形衬底辅助生长、表面原子掺杂及利用超薄SiO2层辅助生长等,以及Ge量子点的演变及组分变化.