GaAs surface passivation by plasma-enhanced atomic-layer-deposited aluminum nitride

A low-temperature passivation method for GaAs surfaces is investigated. Ultrathin AlN layers are deposited by plasma-enhanced atomic-layer-deposition at 200 ° C on top of near-surface InGaAs/GaAs quantum well structures. A significant passivation effect is seen as shown by up to 30 times higher photoluminescence intensity and up to seven times longer lifetime compared to uncoated reference samples. The improved optical properties are accompanied by a redshift of the quantum well photoluminescence peak likely caused by a combination of the nitridation of the GaAs capping layer and a surface coupling effect.     

Electrical characteristics of SiGe-on-insulator nMOSFET and SiGe-silicon-on-aluminum nitride nMOSFET

This paper investigates the electrical characteristics and temperature distribution of strained Si/SiGe n-type metal oxide semiconductor field effect transistor(nMOSFET) fabricated on silicon-on-aluminum nitride(SOAN) substrate.This novel structure is named SGSOAN nMOSFET.A comparative study of self-heating effect of nMOSFET fabricated on SGOI and SGSOAN is presented.Numerical results show that this novel SGSOAN structure can greatly eliminate excessive self-heating in devices,which gives a more promising application for silicon on insulator to work at high temperatures.     

Deposition of aluminum nitride thin film on Si(1 1 1) by KrF excimer laser and its characterizations

We present the deposition of aluminum nitride (AlN) thin film by KrF excimer laser sputtering and the study of the effects of substrate temperature and laser fluences. Deposition rate of AlN thin film at 0.3 Å/pulse has been achieved with laser fluence of 1500 mJ/cm² and at substrate temperature of 250 K, and this shows the enhancement of the deposition rate at low substrate temperature. Surface morphology of the deposited films is characterized by atomic force microscopy (AFM). In addition, the electrical performance of the MIS devices with AlN thin films prepared in this experiment has been characterized.     

Electrical performance of gallium nitride nanocolumns

The electrical characterization of gallium nitride (GaN) nanocolumns with a length up to 1 μm and a diameter of about 30–80 nm grown on doped silicon is a challenge for nano analytics. To determine the conductivity of these nanocolumns, I–V characteristics were recorded by atomic force microscopy (AFM). To measure the conductivity of a single nanocolumn, a conductive AFM tip was placed at the top of the nanocolumn. The measured current/voltage characteristic of a single nanocolumn shows the typical performance of a Schottky contact, which is caused by the contact between the metallic AFM tip and the semiconductor material of the nanocolumn. The height of the Schottky barrier is dependent on the work function of the AFM tip metal used. The linear part of the curve was used to calculate the differential resistance, which was found to be about 13 Ω cm and slightly dependent on the diameter.     

Increasing the thermal conductivity of boron nitride and aluminum nitride particle epoxy-matrix composites by particle surface treatments

The thermal conductivity of boron nitride and aluminum nitride particle epoxy-matrix composites was increased by up to 97% by surface treatment of the particles prior to composite fabrication. The increase in thermal conductivity is due to decrease in the filler-matrix thermal contact resistance through the improvement of the interface between matrix and particles. Effective treatments for BN involved acetone, acids (nitric and sulfuric) and silane. The most effective treatment involved silane such that the coating resulted from the treatment amounted to 2.4% of the weight of the treated BN. The effectiveness of a treatment was higher for a larger BN volume fraction. At 57 vol.% BN, the thermal conductivity reached 10.3 W/ m·K. The treatments had little effect on the specific surface area of the BN particles. Silane treatments were also effective for AlN. At 60 vol.% AlN, the thermal conductivity reached 11.0 W/m·K.     

In掺杂氮化亚铜薄膜的电学、光学和结构特性研究

采用射频磁控溅射方法, 在低功率和低温条件下利用纯氮气作为反应溅射气体制 备出不同In含量的三元氮化物Cu_xIn_yN薄膜. 研究发现In掺杂浓度对薄膜微结构、形貌、表面化学态以及光学特性有灵敏的调节作用. 光电子峰、俄歇峰、俄歇参数的化学位移变化从不同角度揭示了不同含量In掺杂引 起的原子结合情况的变化. XPS结果显示In含量小于8.2 at.%的样品形成了Cu-In-N键. 对In含量为4.6 at.%的样品进行XRD和TEM结构测试, 实验结果肯定了In原子填充到Cu₃N的反ReO₃结构的体心位置. 并且当In含量增至10.7 at.%时, 薄膜生长的择优取向从之前占主导地位的(001)方向转变为(111)方向. 此外, 随着In含量的增加, 薄膜的R-T曲线从指数形式变为线性. 当In含量为47.9 at.%时, 薄膜趋于大温区恒电阻率材料, 电阻温度系数TCR仅为-6/10000. 光谱测量结果显示In摻杂使得氮化亚铜掺杂薄膜的光学帯隙从间接帯隙变为直接帯隙. 由于Burstein-Moss效应, 帯隙发生蓝移, 从1.02 eV 到2.51 eV, 实现了帯隙连续可调. 关键词： 三元氮化物 薄膜 光学特性 氮化亚铜     

Synthesis of boron nitride nanostructures from catalyst of iron compounds via thermal chemical vapor deposition technique

For the first time, patterned growth of boron nitride nanostructures (BNNs) is achieved by thermal chemical vapor deposition (TCVD) technique at 1150 °C using a mixture of FeS/Fe₂O₃ catalyst supported in alumina nanostructured, boron amorphous and ammonia (NH₃) as reagent gas. This innovative catalyst was synthesized in our laboratory and systematically characterized. The materials were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The X-ray diffraction profile of the synthesized catalyst indicates the coexistence of three different crystal structures showing the presence of a cubic structure of iron oxide and iron sulfide besides the gamma alumina (γ) phase. The results show that boron nitride bamboo-like nanotubes (BNNTs) and hexagonal boron nitride (h-BN) nanosheets were successfully synthesized. Furthermore, the important contribution of this work is the manufacture of BNNs from FeS/Fe₂O₃ mixture.     

Structural and optical properties of RF magnetron sputtered aluminum nitride films without external substrate heating

We report structural and optical properties of aluminum nitride (AlN) thin films prepared by RF magnetron sputtering. A ceramic AlN target was used to sputter deposit AlN films without external substrate heating in Ar-N₂ (1:1) ambient. The X-ray diffraction and high resolution transmission electron microscopy results revealed that the films were preferentially oriented along c-axis. Cross-sectional imaging revealed columnar growth perpendicular to the substrate. The secondary ion mass spectroscopy analysis confirmed that aluminum and nitrogen distribution was uniform within the thickness of the film. The optical band gap of 5.3 eV was evaluated by UV-vis spectroscopy. Photo-luminescence broad band was observed in the range of 420-600 nm with two maxima, centered at 433 nm and 466 nm wavelengths related to the energy states originated during the film growth. A structural property correlation has been carried out to explore the possible application of such important well oriented nano-structured two-dimensional semiconducting objects.     

SrTiO3金属-绝缘体-半导体结构的介电与界面特性

采用金属有机分解法在p型Si衬底上制备了SrTiO3（STO）薄膜.研究了STO薄膜金属 绝缘体 半导体(MIS)结构的介电和界面特性.结果表明，STO薄膜显示出优异的介电性能，在10kHz处的介电常数约为105，损耗低于001，这来源于多晶结构和良好的结晶性；MIS结构中的固定电荷密度Nf和界面态密度Dit分别约为15×1012cm-2和(14—35)×1012cm-2eV-1，这主要与Si/STO界面处形成的低介电常数界面层有关. 关键词： SrTiO3薄膜 MIS结构 介电性能 Si/STO界面     

Chloride Assisted Growth of Aluminum Nitride Nanobelts and Their Enhanced Dielectric Responses

通过氯化物辅助的气-固生长方法成功地制备出了大量单晶的氮化铝纳米带. X射线衍射、透射电子显微镜以及选区衍射分析表明,所制备的纳米带是纯度高、结构均匀的单晶体,并具有六方的晶体结构. 显微观察表明所获得的氮化铝纳米带没有缺陷,其生长方向为[0001]方向. 测量了产物在50 Hz 到5 MHz范围内的介电频谱,谱图分析表明样品中的界面对样品的介电特性有很大的影响. 室温条件下,与氮化铝微米粉相比,氮化铝纳米带的介电常数高得多,并在低频情况下尤为显著.     

Inter-diffusion of cobalt and silicon through an ultra thin aluminum oxide layer

Optical emission spectroscopy of sputtered species during ion bombardment, Auger electron spectroscopy and high-resolution transmission electron microscopy were used to study the cobalt and silicon diffusion through the interfaces of Co/AlO/Si(0 0 1) hetero-structure. The results are discussed as a function of the annealing temperature of sample and show that the diffusion process at the interfaces starts for annealing temperatures above 200 °C without detectable modification of the oxide layer.     

Microstructural evolution and dielectric properties of 1D AlN powders synthesized by microwave technique

Low temperature synthesis of Aluminum nitride (AlN) powders through NH₄Cl assisted nitridation have been studied by microwave technique. The effect of processing time on the synthesis of AlN powders has been investigated. The optimum processing time was determined to be 120 min at 630 W, 200 °C. The powders were characterized by X-ray diffraction method (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray analyzer (EDS), Fourier transform infrared spectrometer (FTIR) and Impedance analyzer. XRD results revealed that the product has wurtzite phase of AlN. SEM micrographs show a 1D nanorod of AlN with a granular morphology. FTIR spectra exhibit A1 (TO) and E1 (LO) modes of wurtzite AlN. Dielectric properties of the powders were investigated by means of C–V and C–f and ε′–f characteristics. The reported results indicate a reasonable quality of the obtained AlN powders with high dielectric constant, suitable for application in the fabrication of specific electronic devices.     

Electrical and memory properties of silicon nitride structures with embedded Si nanocrystals

In this work, the electrical and memory behaviour of metal-silicon nitride-silicon structures with an embedded nanocrystalline silicon layer, which either consists of separated silicon nanocrystals, or is a continuous nanocrystalline layer, are presented. The structures were prepared by low-pressure chemical vapour deposition (LPCVD). The effect of the duration of deposition and the structure of the nanocrystalline layer were studied. The writing/erasing behaviour was similar for all the structures, but the retention properties were much worse in the structure with a continuous nanocrystalline layer, than in the structures with separated Si nanocrystals. This indicates that Si nanocrystals play role in charge storage in the studied structures.     

Deposition of hydrogenated amorphous carbon nitride films by dielectric barrier discharge plasmas

Hydrogenated amorphous carbon nitride (a-C:N:H) films were synthesized from CH₄/N₂, C₂H₄/N₂ and C₂H₂/N₂ mixtures using dielectric barrier discharge (DBD) plasmas. Atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphology, bonding structure, and composition of the a-C:N:H films. The influences of plasma parameters (discharge pressure in the range of 25-1000 Pa) and feed gases used on the composition and the structure of deposited films were systematically studied. The a-C:N:H films with the uniform surface structure were deposited by low-pressure DBD plasmas with various systems. Compared to the films deposited in C₂H₄/N₂ and C₂H₂/N₂ systems, the films deposited in the CH₄/N₂ system exhibit the relatively lower surface roughness and deposition rate. For all the films prepared in these three systems, increasing the discharge pressure leads to an increase in film surface roughness and deposition rate. Significant differences among the FTIR spectra of all deposited a-C:N:H films were also observed. Both FTIR and XPS spectra show that for all the films deposited in three different systems, increasing the N₂ fraction leads to a decrease in the H content of deposited a-C:N:H films and an increase in the N content. The properties of deposited films may change from those of polymerlike to diamond-like when the discharge pressure is increased. Correlations between the film properties and growth processes are discussed in this study.     

碳泡沫衬底上氮化铝纳米线的生长及其光致发光特性研究

为了简化了AlN/C复合泡沫材料的制备流程, 本文采用复分解反应法制备AlN纳米材料, 并通过800℃退火处理使其在碳泡沫衬底上重结晶为六方相AlN纳米线. 通过形貌表征测试, 纳米线为表面光滑的长直形圆柱体, 直径约50 nm, 长度10 μm以上, 在碳微球表面沿[001]方向生长. 同时, 采用VLS生长机理对纳米线的生长进行了解释. 对样品光致发光谱的研究表明, 中心波长423 nm处存在一尖锐发光峰且随温度升高发生明显的红移现象, 系C替N杂质能级跃迁发光所致. 样品在紫光波段具有良好的光致发光特性, 有望应用于光探测器领域.     

Growth of β-gallium oxide nanostructures by the thermal annealing of compacted gallium nitride powder

Various β-gallium oxide (β-Ga₂O₃) nanostructures such as nanowire, nanobelt, nanosheet, and nanocolumn were synthesized by the thermal annealing of compacted gallium nitride (GaN) powder in flowing nitrogen. We suggest that Ga₂O₃ vapor might be formed by the reaction of oxygen with the gaseous Ga formed by GaN decomposition. The Ga₂O₃ vapor diffuses into voids derived by compacting GaN powder and is supersaturated there, resulting in the growth of Ga₂O₃ nanostructures via the vapor–solid (VS) mechanism. Ga₂O₃ plate-like hillocks and nanostructures were also grown on the surface of a c-plane sapphire placed on the GaN pellet.     

The influence of high pressures on structure and properties of silicon nitride

Abstract

Silicon nitride as a material with both small coefficient of thermal expansion and high oxidation resistance has long attracted the attention of specialists in various fields of science and technology'. Covalent bonding in this compound is the reason for the use of high temperature sintering.     

Terahertz time domain spectroscopy of hydrothermally synthesized boehmite and ammonium dawsonite nanostructures

The frequency dependent optical and dielectric properties of boehmite (AlOOH) and ammonium aluminum carbonate hydroxide (AACH) nanostructures, prepared at different temperatures via hydrothermal synthesis, were studied by using terahertz time domain spectroscopy (THz-TDS). The complex refractive indices, absorption coefficients and complex dielectric constants were determined and compared for different synthesis temperatures. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were also performed to confirm the formation of boehmite and AACH. Scanning electron microscopy (SEM) was performed to study the morphology of nanostructures. The study reveals the formation of AACH at higher temperatures and decrease in refractive index with increasing synthesis temperature. The higher absorption coefficient and lower refractive index and dielectric constant were observed for AACH than for boehmite.     

First principle study of unzipped boron nitride nanotubes

Systematic first principle calculations have been used to explain the dangling bonds behaviour in the rolling up of a boron nitride nanoribbon (BNNR) to construct a single-walled boron nitride nanotube (BNNT). We found in armchair BNNR two degenerate dangling bonds split and move up to higher energies due to symmetry breaking of system. While in zigzag BNNR changing the topology of system does not affect on metallic features of the band structure, but in unzipped BNNT case a metallic-semimetallic phase transition occurs. Considering the width dependent electronic properties of hydrogen passivated armchair BNNRs, exhibit zigzag behaviour of energy gap in agreement with previous results.