Residual damage effects on gate contacts formed on SiC surfaces etched by using the amorphization technique

A trench fabrication process has been proposed and experimentally demonstrated for silicon carbide using the amorphization technique. In the present work, the quality of gates [oxide for metal oxide semiconductor field-effect transistors (MOSFETs) and Schottky barrier contacts for metal semicondcutor field-effect transistors (MESFETs)] fabricated on the etched surfaces are compared with those formed on the as-grown silicon carbide surface. The resistivity and breakdown electric field of the thermal oxide grown on the etched surface was found to be comparable to that of thermal oxide grown on silicon. However, a large concentration of acceptor type interface states (0.5-1 x 10¹³ cm⁻²eV⁻¹) was observed. This results in a large negative interface charge at room temperature and a significant shift in flat band voltage as a function of temperature, which makes the process unsuitable for formation of gates in UMOSFETs. Titanium Schottky contacts formed on the etched surface showed superior reverse current-voltage characteristics and higher breakdown voltages than the Schottky diodes formed on unetched surface with similar doping concentrations. This indicates that the argon implant process for trench formation is suitable for fabrication of gate regions in high voltage vertical MESFETs (or SITs).     

望远镜红膜物镜色度设计与检验初探

在红膜的设计与低镀制过程中，由于影响薄膜的因素较多，因而实际镀制的红膜射颜色是不一致的，造成了红膜标准的多样性。为此，本文将从色度计量方面给出设计的具体要求：从光谱特性曲线计算红物镜的透射色度和反射色度，即XYZ表色系统的色度坐标值（X、Y、Z）及其取值范围、色饱和度以及检验时的光路、光源等。     

Effect of thin film coating of Au on joint strength in invar-invar packages

The effect of a thin film coating of Au on the joint strength, weld width, and penetration depth in laser welding techniques for Invar-Invar packages is investigated experimentally. It is found that the joint strength, weld width, and penetration depth are strongly dependent on the coating of Au thickness on the Invar material. The welded joints with thick Au coating show narrower weld width, shallower penetration, and hence less joint strength than those of the packages with thin Au coating. The increase in both the thermal conductivity and the vapor volume in the welded joints as the coating of Au thickness increases are the possible mechanisms for the reduction. Detailed knowledge of the effect of thin film coatings of Au on the welded materials, which gives both the highest joint strength and good adhesion, is essential for practical design and fabrication of reliable optoelectronic packaging.     

KrF Laser-induced Damage to ZrO_2/SiO_2 Coatings

ＫｒＦＬａｓｅｒ－ｉｎｄｕｃｅｄＤａｍａｇｅｔｏＺｒＯ_２／ＳｉＯ_２Ｃｏａｔｉｎｇｓ￥ＷＡＮＧＮａｉｙａｎ；ＧＡＯＨｕａｉｌｉｎ（ＣｈｉｎａＩｎｓｔｉｔｕｔｅｏｆＡｔｏｍｉｃＥｎｅｒｇｙ，Ｐ．Ｏ．Ｂｏｘ２７５－７，Ｂｅｊｉｊｎｇ１０２４１３，Ｃｈｉｎ...     

镀减反射膜后半导体激光器端面反射率谱的测量

比较相同偏置条件下镀减反射膜前后的半导体激光器端面自发辐射谱，测得了端面反射率随波长变化的关系曲线。该方法突破了Ｋａｍｉｎｏｗ法单一波长测量的限制，同时也避免了Ｋａｍｉｎｏｗ法在两端面镀膜后所遇到的调制度过小的问题。实验中确定出了低于８×１０（－５）的第二镀膜端面反射率。     

Electron spin resonance study of defects in CVD-grown 3C-SiC irradiated with 2MeV protons

Electron spin resonance (ESR) was used to study defects induced by 2MeV-proton irradiation in cubic silicon carbide (3C-SiC) epitaxially grown on Si substrates by chemical vapor deposition. A new ESR signal labeled T5 was observed at temperatures lower than ≈100 K in Al doped, p-type 3C-SiC epilayers irradiated. The T5 signal has anisotropic g-values of g₁ = 2.0020 ± 0.0001, g₂ = 2.0007 ± 0.0001,and g₃ = 1.9951 ± 0.0001. The principal axes of the g-tensor were found to be along the 〈100〉 directions, indicating that the T5 center has D₂ symmetry. Isochronal annealing of the irradiated epilayers showed that the T5 center was annealed at temperatures around 150° C. A tentative model is discussed for the T5 center.     

Effects of potassium on the reaction pathway of C3H7 species over Mo2C/Mo (1 0 0)

The adsorption and surface reactions of propyl iodide on clean and potassium-modified Mo₂C/Mo(1 0 0) surfaces have been investigated by thermal desorption spectroscopy (TPD), X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) in the 100-1200 K temperature range. This work is strongly related to the better understanding of the catalytic effect of Mo₂C in the conversion of hydrocarbons. Potassium was found to be an effective promoter: it induced the rupture of C-I bond in the adsorbed C₃H₇I even at 100 K. The extent of C-I bond scission varied approximately linearly with the concentration of K coverage at the adsorption temperature of 100 K. As revealed by HREELS and TPD measurements the primary products of the dissociation are C₃H₇ and I. The former one was stabilized by potassium and underwent dehydrogenation and hydrogenation to give propene and propane. The desorption of both compounds is reaction-limited process. A fraction of propyl groups was converted into di-σ-bonded propene, which was stable up to ∼380 K. The coupling reaction of propyl species was also facilitated by potassium and resulted in the formation of hexane and hexene with T_p ∼ 230-250 K. Hydrogen was released with T_p = 390 K, indicative of a desorption limited process. The effect of potassium was explained by the extended electron donation to adsorbed propyl iodide in one hand, and by the direct interaction between potassium and I on the other hand. This was reflected by the shift of the desorption of potassium from the coadsorbed layer at and above 1.0 ML to higher temperature, and by the coincidal T_p values (∼700 K) of potassium and iodine. The formation of KI was also supported by the appearance of a loss feature at 650 cm⁻¹ in the HREEL spectra attributed to a phonon mode of KI.     

Structural characterization of oxide layers thermally grown on 3C-SiC films

The oxidation of 3C-SiC films deposited on off-oriented Si(001) substrates by reactive magnetron sputtering has been studied. The oxidation was carried out using dry conditions at a temperature of 1200°C. The composition of the oxide layer was investigated by Auger electron spectroscopy (AES). The oxide layer was found to contain no C except for the region very close to the interface, and the stoichiometry was found to be close to that of SiO₂. Cross-sectional transmis-sion electron microscopy (XTEM) showed the oxide layer to be completely amorphous, dense, and homogeneous with a uniform thickness. High-resolution XTEM imaging showed an atomically sharp SiO₂/SiC interface.     

Peculiarities of silicon carbide crystal growth under the diffusion mechanism of vapour transfer

In the present work the gas dynamics in the growth zone of SiC crystals is investigated. It is shown that the propagation of SiC vapour from the growth cavity walls towards the lids is effected by diffusion. On this basis the calculation of the concentration distribution of SiC vapour (n), the equilibrium vapour concentration (n_s) and the supersaturation (α = [(n – n_s)/n_s] × 100%) in the crystal growth zone at different radial and axial gradients is carried out by solving the Laplace equation in cylindrical co-ordinates for a stationary case corresponding to the conditions of crystal growth. The results obtained are compared with the available experimental data, which gives the possibility of explaining some of the observed peculiarities during SiC crystal growth from the vapour phase by the sublimation method.     

碳化硅薄膜及压阻效应研究

研究了SiC薄膜的制备及其压阻特性。利用热丝化学气相沉积(HFCVD)法在硅(111)晶面制备SiC薄膜,对制备的薄膜进行X射线衍射分析和其它测试。结果表明:SiC薄膜晶向取向一致,薄膜生长速率为3 m / h,厚度约为5 m。同时,利用高阻仪研究该薄膜的压阻特性,测得应变量()在(2~6)×104范围内,电阻的相对变化量(ΔR·R1)和压阻灵敏度因子(k)随应变量()的变化曲线。结果表明该薄膜有明显的压阻效应。