MgO和Si上NbN超薄薄膜的生长研究

我们在单晶MgO(100)、Si(100)和SiOx/Si基片上成功生长了纳米厚度的超薄NbN薄膜,利用现代分析手段:X射线衍射(XRD)、透射电子显微镜(TEM)、原子力显微镜(AFM)等技术分析研究了所制备的超薄NbN薄膜的微观结构、厚度、表面界面情况等物理特性。研究表明,在MgO(100)基片上获得了外延生长的单晶NbN超薄薄膜,在Si(100)和SiOx/Si基片上获得的是多晶NbN超薄薄膜。厚度均约6nm左右。这些超薄薄膜的超导转变温度分别为:MgO上薄膜是14.46K,Si和SiOx上薄膜分别是8.74K和9.01K.     

Influence of Cr<Superscript>+</Superscript> ion implantation and pulsed ion-beam annealing on the formation and optical properties of Si/CrSi<Subscript>2</Subscript>/Si(111) heterostructures

The effect of pulsed ion-beam annealing on the surface morphology, structure, and composition of single-crystal Si(111) wafers implanted by chromium ions with a dose varying from 6 × 10¹⁵ to 6 × 10¹⁶ cm⁻² and on subsequent growth of silicon is investigated for the first time. It is found that pulsed ion-beam annealing causes chromium atom redistribution in the surface layer of the silicon and precipitation of the polycrystalline chromium disilicide (CrSi₂) phase. It is shown that the ultrahigh-vacuum cleaning of the silicon wafers at 850°C upon implantation and pulsed ion-beam annealing provides an atomically clean surface with a developed relief. The growth of silicon by molecular beam epitaxy generates oriented 3D silicon islands, which coalesce at a layer thickness of 100 nm and an implantation dose of 10¹⁶ cm⁻². At higher implantation doses, the silicon layer grows polycrystalline. As follows from Raman scattering data and optical reflectance spectroscopy data, semiconducting CrSi₂ precipitates arise inside the silicon substrate, which diffuse toward its surface during growth.     

Surface morphology and reaction at Cu/Si interface—Effect of native silicon suboxide

Copper thin films are deposited by thermal evaporation on unetched and etched monocrystalline silicon. The study by alpha particles backscattering (RBS) raises a strong diffusion of copper in silicon substrates with and without native suboxide layer. On the other hand, the X-rays diffraction shows the formation and the growth of Cu₃Si and Cu₄Si silicides. Whereas the scanning microscopy underlines large crystallites growth surrounded by black zones of silicon coming from the uncovered substrate, independently to the surface state of the substrate, after annealing at high temperature. The presence of native silicon suboxide at Cu/Si interface, influences in a drastic way the minimal temperature to which the interfacial reaction occurs. The oxygen impurities detected by microanalysis, after heat treatment under vacuum, are closely related to the growth of silicides crystallites.     

Effect of titanium ion implantation and the gas atmosphere on the electrophysical properties of alumina

The energy and kinetic characteristics of the dark conductivity and photoconductivity of polycrystalline alumina irradiated by titanium ions and then annealed in vacuum and air have been studied. The effect of temperature on the properties and electron-transport mechanisms is determined. In the air pressure range from 10⁵ to 1 Pa, the electrophysical properties are reversible. A semiconductor coating can be formed on the alumina surface via vacuum annealing; when heated in air, it becomes insulating. The reverse transition is also possible. These modifications are related to the formation of defects, accumulation of oxygen-containing complexes, and changes in the stoichiometric compositions of the compounds synthesized by the ion thermal treatment.     

Positive mouns in iron: Dipolar fields at tetrahedral sites and jump frequencies at low temperatures

On polycrystalline and monocrystalline iron muon-spin precession frequencies and transverse relaxation rates have been measured down to 0.5 K. In the polycrystalline sample two distinct precession frequencies were observed at and below 1.4 K. They are attributed to the different dipolar fields at magnetically inequivalent tetrahedral interstices seen by muons moving locally around impurities. By contrast, in monocrystalline iron we observed only one precession frequency in monocrystalline iron with a damping rate which increased with decreasing temperature down to 0.5 K. We attribute the difference between the monocrystalline and the polycrystalline sample to different impurity contents. The single-crystal data are discussed in terms of μ⁺ diffusion by hopping between interstitial sites of tetragonal symmetry. The answer to several open questions is expected from an extension of the measurements to lower temperatures.     

Structural, optical and electrical properties of amorphous silicon thin films prepared by sputtering with different targets

Amorphous silicon (a-Si) films were prepared by sputtering method with polycrystalline and monocrystalline silicon targets. Structural, optical and electrical properties of the a-Si films have been systematically studied. The deposition power is from 100 to 200 W. Compared with the a-Si films deposited by using monocrystalline silicon target, the a-Si films prepared with polycrystalline silicon target exhibit better growth property, similar optical band gap, and own the highest mobility of 1.658 cm²/Vs, which make a good match with the optimal window of optical band gap for a-Si solar cells. The results indicated that the polycrystalline silicon target is superior to the monocrystalline silicon target when used to prepare a-Si films as the intrinsic layer in a-Si solar cells.     

Electrical properties of Cd,Zn and S ion-implanted layers in GaAs

The electrical properties of cadmium, zinc, and sulfur ion-implanted layers in gallium arsenide have been measured by the van der Pauw-Hall technique. Ion implantation was performed with the substrates held at room temperature. The dependence of sheet resistivity, surface carrier concentration, and mobility on ion dose and on post-implantation anneal temperature was determined. In the case of 60 keV Cd⁺ ions implanted into n-type substrates, a measurable p-type layer resulted when samples were annealed for 10 minutes at a temperature in the range 600—900°C. After annealing at 300—900°C for 10 minutes, 100 per cent electrical activity of the Cd ions resulted for ion doses ≤ 10¹⁴/cm².

The properties of p-type layers produced by implantation of 85 keV Zn⁺ ions were similar to those of the 60 keV cadmium-implanted layers, in that no measurable p-type behavior was observed in samples annealed below a relatively high temperature. However, in samples implanted with 20 keV Zn⁺ ions a p-type layer was observed after annealing for 10 minutes at temperatures as low as 300°C.

Implantation of sulfur ions into p-type GaAs substrates at room temperature resulted in the formation of a high resistivity n-type layer, evcn before any annealing was performed. Annealing at temperatures up to 200°C or above 600°C lowered the resistivity of the layer, while annealing in the range 300—500°C eliminated the n-type layer.     

利用磁控溅射技术在熔融石英衬底上生长铟锡氧薄膜的结构和形貌特性研究

利用磁控溅射技术在熔融石英衬底上沉积铟锡氧薄膜(ITO),讨论了生长温度、沉积时间、激光辐照和退火对ITO薄膜结构及形貌的影响.随着沉积温度的升高和沉积时间的延长,薄膜的晶化程度得到明显的改善,方块电阻降低,并且薄膜的形貌从光滑表面的圆形多晶颗粒演变到枝杈形貌.短时间的脉冲激光辐照使得枝杈的尖状晶粒变得圆滑,导电性略有改善.ITO薄膜在可见光区的透过率在经过空气中退火处理后明显得以改善,平均透过率可以达到80%.     

AES studies of palladium films formed on copper and mica

Thin epitaxial films of palladium were grown on epitaxial copper films and cleaved mica in ultra high vacuum. The growth modes of these films were investigated by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), transmission electron microscopy (TEM), and TEM replica techniques. Layer by layer growth of Pd on Cu and mica was observed and inelastic mean free paths of Auger electrons for energies of 60 eV (Cu MMM) and 329 eV (Pd MNN) were calculated. These values were 5.7 and 6.9 Å respectively. The thermal stability of monocrystalline and polycrystalline Pd/Cu bilayer films at 483 K was also investigated by AES and TEM. It was found that Pd agglomerates on the Cu at this temperature to form a Stranski-Krastanov growth morphology. The agglomeration is much more rapid on polycrystalline films, suggesting that high surface diffusivity paths (grain boundaries and possibly other defects) enhance the surface diffusion of Pd on Cu.     

Crystallization and surface morphology of Au/SiO2 thin films following furnace and flame annealing

A crystallization and surface evolution study of Au thin film on SiO₂ substrates following annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared by conventional evaporation of gold in a high vacuum (10⁻⁷ mbar) environment on substrates at room temperature. Thermal treatments were performed by both furnace and flame annealing techniques. Au thin films can be crystallized on SiO₂ substrates by both furnace and flame annealing. Annealing arranges the Au crystallites in the (1 1 1) plane direction and changes the morphology of the surface. Both, slow and rapid annealing result in a good background in the XRD spectra and hence clean and complete crystallization which depends more on the temperature than on the time of annealing. The epitaxial temperature for the Au/SiO₂ system decreases in the range of 350-400 °C. Furnace and flame annealing also form crystallized gold islands over the Au/SiO₂ surface. Relaxation at high temperatures of the strained Au layer, obtained after deposition, should be responsible for the initial stages of clusters formation. Gold nucleation sites may be formed at disordered points on the surface and they become islands when the temperature and time of annealing are increased. The growth rate of crystallites is highest around 360 °C. Above this temperature, the layer melts and gold diffuses from the substrate to the nucleation sites to increase the distance between islands and modify their shapes. Well above the eutectic temperature, the relaxed islands have hexagonally shaped borders. The mean crystallite diameters grow up to a maximum mean size of around 90 nm. The free activation energy for grain boundary migration above 360 °C is 0.2 eV. Therefore the type of the silicon substrate changes the mechanism of diffusion and growth of crystallites during annealing of the Au/Si system. Epitaxial Au(1 1 1) layers without formation of islands can be prepared by furnace annealing in the range of 300-310 °C and by flame annealing of a few seconds and up to 0.5 min.     

Reactive Solid State Dewetting: Interfacial Cavitation in the System Ag-Ni-O

Micron thick silver films, vapour deposited onto high purity polycrystalline nickel substrates, dewet the substrate after high temperature annealing in oxygen rich atmospheres, while the films remain stable after annealing at the same temperature in a nitrogen atmosphere. Dewetting occurs when a nickel oxide layer is formed at the silver-nickel interface as a consequence of oxygen diffusion through the silver film.The sensitivity of the dewetting process on various parameters such as the annealing: temperature, time and oxygen partial pressure has been determined.Scanning Electron Microscopy (SEM) of cross-sections reveal that the main mechanism of dewetting at short annealing time is the nucleation of cavities at the Ag-NiO interface which grow towards the free surface of the Ag film. They are formed not only at Ag grain boundaries and triple junctions but also in the core of Ag grains. Such cavities do not occur when the Ag film is deposited onto a NiO single crystal. We propose a simple model for the cavitation: a vacancy supersaturation is sustained in Ag, at the Ag-NiO interface, as a result of oxygen consumption by the oxidation reaction. In regions of fast oxidation, the vacancy supersaturation is large enough to promote the nucleation and growth of interfacial cavities. The model qualitatively accounts for all the observed trends; quantitatively, on top of the vacancy supersaturation, extra-contributions to the driving force for cavitation must be invoked.     

快速热退火对Co/Si0.85Geo.15肖特基结电学特性的影响

用离子束溅射技术分别在SiO2和单晶Si衬底上沉积了Si1-xGex和Co薄膜.在不同温度下,对Co/Si1-xGex肖特基结进行快速热退火处理(RTA),对处理后的样品进行了表面形貌和电学测量.发现退火温度升高,样品表面粗糙度变大,理想因子也变大,但对肖特基势垒高度(SBH)的影响很小.分析认为,随着退火温度的升高,...     

Ni离子注入多晶ZrO2的表面电性能和结构

对氧化钇(Y₂O₃)部分稳定氧化锆(ZrO₂)样品在室温下进行了Ni离子注入(140kev,5×10¹⁵-2×10¹⁷ios/cm²)和热退火处理.应用电学测量,Rutherford背散射技术(RBS),X射线光电子能谱(XPS)和喇曼光谱方法研究了Ni离子注入多晶ZrO₂的表面电性能,注入层结构及其热退火的影响。     

Determination of the Oxygen Diffusion Coeficient in Polycrystalline Li-Ti Ferrites

Two independent methods, the isotope method based on nuclear microanalysis and the method based on measuring the electronic-conductivity activation energy, are used to determine the grain-boundary diffusion and volume diffusion of an oxygen isotope ¹⁸O in a polycrystalline lithium-titanium ferrite at the thermal annealing temperature 1073 K. A comparative analysis is conducted of the potential of the methods in studying oxygen diffusion in the material concerned. It is shown that the technique for obtaining the diffusion parameters from the electronic conductivity measurements allows a comparatively precise determination of both the volume and grain-boundary diffusion coefficients of oxygen in polycrystalline ferrites.     

Photoluminescence properties of Tb in porous silicon

Terbium (Tb³⁺)/porous silicon (PS) nanocomposites have been formed by impregnation of PS layer in chloride solution of terbium. Complete and uniform penetration of Tb³⁺ into PS layer is confirmed by Rutherford backscattering spectrometry (RBS) study. Photoluminescence (PL) spectrum shows that Tb³⁺ ions emit highly in the green region, while the PL band of PS is quenched. The emission of Tb³⁺ ions depends strongly on the excitation energy and shows a high efficiency at 488 nm corresponding to the maximum absorption band in terbium. A systematic study of the PL versus annealing temperature was performed. It shows an important improvement of the PL intensity for 700°C temperature annealing.     

Stress dependence of the magnetic permeability of MnZn ferrous ferrites

In monocrystalline MnZn ferrous ferrites the magnetic permeability μ as a function of temperature T has been observed to show a striking dependence on applied stress. Stresses cause the μ(T) curve to cant around a point near its maximum arising from compensation of the magnetocrystalline anisotropy due to the ferrous ions. By grinding the surface of a monocrystalline toroid, a tensile stress was exerted on the interior of the specimen. The canting of the μ(T) curve observed when the damaged surface layer was removed step by step was employed to study the underlying physical mechanism. In the case of polycrystalline materials the maximum of μ(T) is usually strongly suppressed. Nevertheless, it proved possible to investigate the dependence of μ(T) on applied stress in a polycrystalline MnZn ferrous ferrite pot core.     

Influence of annealing on the concentration profiles of boron implantations in silicon

The influence of annealing on the concentration profiles of boron implanted into silicon with does of 10¹⁴ ions/cm² up to 10¹⁶ ions/cm² and an energy of 70 keV was studied. The concentration profiles were measured with Secondary Ion Mass Spectrometry (SIMS). The broadening of the concentration profiles during annealing can be described as a superposition of effects resulting from a relatively immobile and a mobile boron fraction. The properties of the immobile boron fraction were studied by measuring the influence of a boron implantation on the distribution of a homogeneous boron background dope. From these experiments it was concluded that the immobile boron fraction consists of boron precipitates. The properties of the mobile fraction were studied from concentration profiles that were obtained after annealing during different periods at the same temperature. It was found that during the initial stage of the annealing process a fast broadening of the profile occurs; this was assumed to be due to an interstitial type boron diffusion. After prolonged annealing the much slower substitutional type diffusion prevails, due to trapping of the interstitial boron atoms by vacancies. The reliability of the SIMS method, as applied to profile measurements, was checked for the high boron doses used in this investigation. Excessive boron precipitates, obtained after annealing of a high dose, such as 10¹⁶ ions/cm² at about 1000°C, appear to give some increase of the ion yield.     

Processing for optically active erbium in silicon by film co-deposition and ion-beam mixing

Techniques of film deposition by co-evaporation, ion-beam assisted mixing, oxygen ion implantation, and thermal annealing were been combined in a novel way to study processing of erbium-in-silicon thin-film materials for optoelectronics applications. Structures with erbium concentrations above atomic solubility in silicon and below that of silicide compounds were prepared by vacuum co-evaporation from two elemental sources to deposit 200-270 nm films on crystalline silicon substrates. Ar⁺ ions were implanted at 300 keV. Oxygen was incorporated by O⁺-ion implantation at 130 keV. Samples were annealed at 600 °C in vacuum. Concentration profiles of the constituent elements were obtained by Rutherford backscattering spectrometry. Results show that diffusion induced by ion-beam mixing and activated by thermal annealing depends on the deposited Si-Er profile and reaction with implanted oxygen. Room temperature photoluminescence spectra show Er³⁺ transitions in a 1480-1550 nm band and integrated intensities that increase with the oxygen-to-erbium ratio.     

Reduction of dislocation density and improvement of optical quality in ZnO layers by MgO-buffer annealing

Optical properties of ZnO thin films with/without MgO-buffer annealing were investigated by low and room temperature photoluminescence measurements. The ZnO films were grown on c-sapphire substrates by plasma-assisted molecular-beam epitaxy employing a thin MgO-buffer layer. Dislocation density of ZnO layer was reduced from 5.3 × 10⁹ to 1.9 × 10⁹ cm⁻² by annealing MgO-buffer prior to the growth of ZnO. The intensity of free exciton emission from the sample with MgO-buffer annealing was almost twice of that from the sample without annealing, while the deep level emission from the sample with MgO-buffer annealing was about 1/3 of that without annealing. The MgO-buffer annealing improves optical quality of overgrown ZnO films.     

ZnO nanoparticle creating in a SiO2/Si structure using the Zn ion implantation with subsequent heat treatment

The distribution profiles of the dopant in the surface layer of a SiO₂/Si structure implanted with Zn and O ions are studied via Rutherford backscattering spectroscopy for He²⁺ ions using the channeling technique. The redistribution of implanted impurities in the Si surface layer during the formation process of zinc oxide (ZnO) nanoparticles is analyzed. The effect of the annealing temperature on the formation process and growth of ZnO nanoparticles is studied. The sample-surface morphology is examined via atomic force microscopy. The optical absorption and photoluminescence of the implanted layers are studied.