Directional solidification and microstructures of near-eutectic Cr–Cr3Si alloys

Near-eutectic Cr–Cr₃Si alloys were directionally solidified in a high-temperature optical floating zone furnace. At the eutectic composition, uniform and well-aligned lamellar structures were obtained over a fairly wide range of solidification conditions, but not at very low or very high growth rates where degenerate and cellular structures, respectively, were obtained. The lamellar spacing was found to increase with decreasing solidification rate, in agreement with the Jackson–Hunt theory. In addition, for a fixed growth rate, the lamellar spacing was found to increase with increasing rotation rate. The growth directions in the lamellar eutectic are found to be 1 0 0 for the Cr₃Si phase and 1 1 1 for the Cr solid-solution phase. Eutectic microstructures (rod or lamellar) could also be produced at off-eutectic compositions, but only for a limited range of growth conditions.     

Titanium silicide/germanide formation on submicron features for high mobility SiGe channel field effect transistors

The formation of self-aligned Ti(Si_(1−x)Ge_(x))₂ on submicron lines is described. The silicide/germanide is formed by reacting sputtered Ti with epitaxially grown Si_(1−x)Ge_(x) of composition and thickness relevant to high mobility Si_(1−x)Ge_(x) channel field effect transistors. Ti(Si_(1−x)Ge_(x))₂ formation on narrow lines was carried out on phosphorous doped material, because of the well known difficulties of forming silicide on heavily n-doped silicon. A companion set of boron doped blanket films was also processed. The results show that the process temperature required for the minimization of silicide/germanide sheet resistance is reduced as compared to silicide formation on Si alone. However, the silicide/germanide films agglomerate with increased high temperature processing more easily than pure silicide. The thermal stability is degraded more for films with higher Ge content and is a strong function of dopant type. Silicide/germanide formation on phosphorous doped Si_(1−x)Ge_(x) layers with x = 10% have a line width dependence similar to silicide formation. Formation on phosphorous doped Si_(1−x)Ge_(x) layers with x = 27% display an inverse line width dependence, with higher overall sheet resistance. Formation of silicide/germanide on blanket films of boron doped Si_(1−x)Ge_(x) with x = 27% behaved similar to the formation of silicide on silicon.     

Low-temperature processing of shallow junctions using epitaxial and polycrystalline CoSi2

Cobalt disilicide is grown epitaxially on (100) Si from a 15 nm Co/2 nm Ti bilayer by rapid thermal annealing (RTA) at 900°C. Polycrystalline CoSi₂ is grown on (100) Si using a 15 nm Co layer and the same annealing condition. Silicide/p⁺-Si/n-Si diodes are made using the silicide as dopant source:¹¹B⁺ ions are implanted at 3.5–7.5 kV and activated by RTA at 600–900°C. Shallow junctions with total junction depth (silicide plus p⁺ region) measured by high-resolution secondaryion mass spectroscopy of 100 nm are fabricated. Areal leakage current densities of 13 nA/cm² and 2 nA/cm² at a reverse bias of -5V are obtained for the epitaxial silicide and polycrystalline silicide junctions, respectively, after 700°C post-implant annealing.     

Thermal reliability of n-GaAs/Ti/Pt/Au Schottky contacts with thin Ti films for reduced gate resistance

The thermal stability of Ti/Pt/Au Schottky contacts on n-GaAs with Ti films 0–60 nm is investigated. The contacts with Ti films as small as 10 nm remain thermally stable with annealing up to 400°C. The changes induced by thermal treatment in the electrical characteristics of the contacts are correlated with the Rutherford backscattering and microscopic analysis of the annealed samples. It shows profuse interdiffusion and interfacial reaction with 300°C anneal for the GaAs/Pt/Au system. It has been found that introducing the Ti film between GaAs and Pt/Au, the interdiffusion of Pt and Au is also prevented. These results are useful for reducing the gate metallisation resistance of metal semiconductor field effect transistors.     

Co-deposition of cobalt disilicide on silicon–germanium thin films

The formation of CoSi₂ on strained epitaxial Si_0.8Ge_0.2/Si(100) films has been studied as a function of the deposition method and annealing temperature. Two types of deposition processes were used: a direct method, where 5 nm of pure Co metal were deposited at room temperature onto a strained 80 nm thick Si_0.8Ge_0.2 layer; and a co-deposition method, where 5 nm Co and 18.2 nm Si were simultaneously deposited in a 1:2 ratio onto a strained Si_0.8Ge_0.2 layer at 450°C. Samples were then annealed at temperatures ranging from 500 to 800°C. Extended X-ray absorbance fine structure spectroscopy (EXAFS) and X-ray diffraction (XRD) were used to characterize the structure of the resulting films. It was found that the samples prepared via the direct deposition method did not convert to CoSi₂ at any annealing temperature up to 800°C, while the co-deposited samples formed epitaxial CoSi₂ at even the lowest annealing temperature of 500°C. These results are discussed in terms of proposed reaction mechanisms of the different deposition methods, based on consideration of the Co–Si–Ge ternary phase diagram.     

等离子增强化学气相淀积硅化钛薄膜的特性

本文以四氯化钛（ＴｉＣｌ４）和硅烷（ＳｉＨ４）为源物质，采用等离子增强化学气相淀积（ＰＥＣＶＤ）工艺结合常规热退火制备了优良的ＴｉＳｉ２薄膜。研究了淀积和退火条件对薄膜性质的影响。用四探针检测了退火前后薄膜的薄层电阻，用俄歇电子能谱（ＡＥＳ）和Ｘ射线衍射分析了薄膜的化学组成和晶体结构。     

Thermoelectric Properties and Electronic Structure of Bi- and Ag-Doped Mg<Subscript>2</Subscript>Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Compounds

Mg₂Si_1−x Ge _x compounds were prepared from pure elements by melting in tantalum crucibles. The reaction was conducted under an inert gas in a special laboratory setup. Samples for thermoelectric measurements were formed by hot pressing. Structure and phase composition of the obtained materials were investigated by x-ray diffraction (XRD). Morphology and chemical composition were examined by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS), respectively. Thermoelectric properties, i.e., the Seebeck coefficient, the electrical conductivity, and the thermal conductivity, were measured in the temperature range of 500 K to 900 K. The effect of Bi and Ag doping on the thermoelectric performance of Mg-Si-Ge ternary compounds was investigated. The electronic structures of binary compounds were calculated using the Korringa–Kohn–Rostoker (KKR) method. The effects of disorder, including Ge substitution and Bi or Ag doping, were accounted for in the KKR method with coherent potential approximation calculations. The thermoelectric properties of doped Mg₂Si_1−x Ge _x are discussed with reference to computed density of states as well as the complex energy band structure.     

In-plane light emission of organic light-emitting transistors with bilayer structure using ambipolar semiconducting polymers

The concept of using an ambipolar bilayer semiconducting heterostructure in organic light-emitting transistors (OLETs) is introduced to provide a new approach to achieve surface emission. The properties of top-gate-type bilayer OLETs with ambipolar materials based on two types of fluorene-type polymers used as an emissive layer and an electron blocking layer are investigated. Line-shaped yellow–green emission occurs near a hole-injection electrode. When hole transport is dominant in the upper layer which acts as an electron blocking layer, and electrons are injected into the lower layer, an in-plane light-emitting pattern is observed. The measured in-plane emission zone confirms that both hole and electron transport are determined to occur mainly along the different organic layers between the source and drain electrodes, and an in-plane recombination zone of electrons and holes exists near the bilayer organic interface. This work is anticipated to be useful for the development of in-plane light-emitting transistors.     

Fabrication of high-purity HfSi2 powder via molten salt-assisted magnesium thermal reduction

In this work, high-purity HfSi₂ powders were successfully fabricated via a molten salt-assisted magnesium thermal reduction method using HfO₂ and Si as raw materials. The effects of reaction temperature and time on the formation of HfSi₂ were systemically investigated. The morphological and phase composition of as-prepared HfSi₂ powders were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen/oxygen determinator. The results indicated that as-obtained HfSi₂ powders possess the orthorhombic structure with approximately 6.4 μm in size and the oxygen content as low as 0.20%. This work can provide a novel route to fabricate the high-purity transition metal silicides powders.     

激光熔化沉积γ／Mo2Ni3Si金属硅化物合金的腐蚀行为

采用极化曲线，塔菲尔图（Tafel Plot），交流阻抗（EIS）及浸泡腐蚀技术，研究了激光熔化沉积γ／Mo2Ni3Si合金在不同酸，碱，盐介质中的腐蚀行为。结果表明，该合金在1mol／L NaOH溶液中，由于形成了稳定的钝化膜，耐蚀性优异；在1mol／LH2SO4溶液中，合金只能形成不稳定的钝化膜；而在含Cl^-的中性或酸性介质中，合金没有钝化趋势，且由浸泡腐蚀试验表明，在1mol／LHCl溶液中，由于Cl^-导致相界腐蚀，合金耐蚀性较差。