Electronic properties of undoped polycrystalline silicon

Standard semiconductor measurements and techniques have been applied to undoped, high-purity polycrystalline silicon to determine its electronic properties. Resistivity and Hall mobility were determined as function of temperature, and the ability of polycrystalline silicon to form Schottky barriers and p?i?n junctions has been evaluated experimentally. Present results show Si grain boundaries behaving as p-type layers separating high-resistivity grains. An effective mobility, half the monocrystalline value, and an average carrier density in the 10¹⁵ cm^?3 range are deduced. A qualitative model is discussed to describe present results.     

Electronic properties of polycrystalline ceramic cadmium sulphide

An attempt has been made to explain the current transport mechanism of ceramic cadmium sulphide layers using a semiconductor-grain boundary-semiconductor barrier model. It is shown that a sine-hyperbolic current-voltage relationship holds good for ceramic cadmium sulphide. Grain boundary parameters like potential barrier (φ_B) and average one-electron trapping state density (N_T) in the grain boundary are determined experimentally for the first time for ceramic cadmium sulphide through the study of the current-voltage characteristics and zero-bias capacitances. The variation of φ_B and N_T with temperature (28°C to ?120°C) and bias voltage has also been investigated. It is concluded that the thermionic field emission components of current play a major role in the current transport characteristics of a ceramic cadmium sulphide layer.     

含缺陷态的非线性介质材料的光子晶体的双稳态特性

文章报道了在具有缺陷态的二维非线性介质材料的光子晶体中光的传播特征 ,光子晶体是含有多单元层的简单和复杂周期的介质结构。事实上 ,我们感兴趣的主要是缺陷模式的传播和局域的光强的增强因素。用转移矩阵方法 ,我们计算了光子晶体的电磁场波的传播 ;从而获得局域光的增强效应 ;这种方法计算了有限厚度材料的传播特性 ,数字结果表明非线性介质材料的缺陷结构的光传播能引起输入的光强度的改变 ;这种改变表现出双稳态特征 ;对于简单和复杂的光子晶体 ,假设输入的光强度是稳定的 ;这种双稳态特征就容易出现 ;对于复杂结构的光子晶体 ,则便显出复杂的特征。总的传输量是大的情况 ,双稳态也会出现。另外 ,缺陷介质的饱和吸收系数 ,折射率比值及介质层数值确定了双稳特性的可见性     

Electronic properties of variably charged defects in crystalline semiconductors

The electronic properties of defects with various spatial configurations are examined in relation to corresponding sets of valence bonds. The examination is based on the analysis of the energy functional, in which the elastic energy in the anharmonic approximation, the variation in the electronic term of the defect quasi-molecule defined by the electron localization, and Hubbard’s interaction energy are taken into account. Two types of such defects are recognized, namely, the defects with strong and weak electron-atom interaction. For defects of the first type, which are characterized by positive effective correlation energy, no variations of the adiabatic potential topology are observed after the electron localization. The pair of carbon atoms (C_iC_s) and donor-acceptor pairs in the crystalline silicon belong to this type of defect. The effective occupancy is calculated for this type of defects as a function of adiabatic potential parameters. Transformation of the initial double-well potential into the single-well potential after the localization of the carriers is substantial for the properties of the second type defects. In this case, the effective correlation energy can be either positive or negative. The analysis of the known experimental results permits us to assume that the interstitial boron atom in silicon belongs to this type of defect. The adiabatic potential (in which the interstitial boron atom moves), the activation energies for transitions between different charge states of this defect, and the effective occupancy are calculated from the experimental data reported by Watkins.     

An overview of laminate materials with enhanced dielectric properties

This report focuses on laminate materials (resins and reinforcements) having potential applications in the manufacture of multi-layer printed wiring boards (PWBs) that are required to efficiently transmit high-speed digital pulses. It is intended to be a primer and a reference for selection of candidate materials for such high-performance PWBs. Included are dielectric and physical properties, and where available chemical composition and/or structure, commercial availability, compatibility with typical PWB processing schemes and approximate relative cost. Recommendations are made as to the most viable candidate materials for this type of PWB application, based on a comparison of electrical and physical properties together with processing and cost considerations. The cyanate ester resin system appears promising. Such a resin may be reinforced with regular E-glass, or the more newly available S-glass, to produce a laminate useful for intermediate performance applications. For more demanding applications the E-glass will have to be replaced by a material of much lower relative permittivity. The expanded-PTFE reinforced laminates fromW. L. Gore appear to be a good choice for these applications. The processing of theGore materials can be expected to deviate from that used with FR-4 type materials, but is likely to be less problematic than laminates comprised of a fluorinated resin. Processing is a key obstacle to the implementation of any of the new materials herein. If implementation is to be successful, programs must be established to develop and optimize processing procedures. Cost will remain an important issue. However, the higher cost of the new materials may be justified in high-end products by the performance they deliver.     

Transmission properties of multilayer films composed ofmagneto-optical and dielectric materials

In this paper, we investigated the transmission properties of multilayer films composed of magneto-optical and dielectric materials, in relation to layer stacking structure. The basic structures are made of alternating layers of these materials having a conventional symmetric periodicity with the center of the structure. Films with these basic structures exhibit an enhanced Faraday rotation effect. The rotation increases to an angle close to 45°, which is required for an optical isolator, as the repetition number of alternating layers increases. However, the transmittance decreases in these films as the rotation increases. To clarify the possibility of improving the transmittance, we also investigated films composed of multiple stacks of the basic structures. We found that, by using the multiple stacks, the transmittance can be improved without degrading the rotation characteristics     

溶胶-凝胶法制备SiO_2材料及其微波介电性能研究

采用溶胶-凝胶法制备了非晶SiO_2粉体,并研究了不同溶液配比对所得粉体粒度和分散性的影响。结果表明:当H2O和TEOS摩尔比为20:1和40:1时,可以制备出分散性较好的非晶SiO_2粉体,其粒度分别为700 nm和120 nm。在此基础上,研究了不同原料粉体对SiO_2材料烧结特性和微波介电性能的影响规律。研究发现:粉体粒度较小,有利于降低SiO_2材料的烧结温度,提高其相对密度,抑制其析晶现象。当烧结温度为1050~1200℃时,SiO_2材料的相对介电常数为2.50~3.75,Q·f值为9850~61 272 GHz,τf值的变化范围为±15×10–6/℃(温度范围为25~85℃),适合用于制作微波介质基板。     

Electronic properties of the interface between the organic semiconductor α-sexithiophene and polycrystalline palladium

The interface properties of α-sexithiophene (α-6T) and polycrystalline, atomically clean and contaminated palladium have been studied by combined core level X-ray photoemission spectroscopy and valence band ultraviolet photoemission spectroscopy. Our data indicate for the atomically clean palladium substrate a chemical reaction between the α-sexithiophene molecules and the substrate during the formation of a monolayer of flat lying α-6T molecules. We find an interface dipole of −1.2 eV and an injection barrier for holes of about 0.7 eV. In the case of ex-situ treated, contaminated palladium as metal electrode material we find a reduced interface dipole −0.4 eV and hole injection barrier 0.5 eV. By the comparison to the results of α-sexithiophene on gold we demonstrate the importance of the strength of chemical reactions at the interface.     

基于不同介质材料的AOTF特性研究综述

基于不同介质材料的AOTF(声光可调谐滤波器)具有不同的性质及应用场合.目前应用于紫外、可见光和红外波段的AOTF主要以α-SiO2、TeO2和TAS( Tl3AsSe3)为介质.为了得到性能更优的AOTF,人们一直在探寻新型双折射晶体材料来代替α-SiO2和TAS.文章汇总并讨论了近年来人们针对基于TeO2、KDP(...     

Low dielectric constant materials

The more advanced an integrated circuit becomes, the more stringent are the demands for certain properties of a dielectric or insulating material. In addition, it is essential that the layer maintain its specific electrical, physical, and chemical properties after incorporation in the device structure and during subsequent processing. Due to temperature budget constraints and the accelerated decrease of feature sizes below 0.25 μm, one can no longer rely on traditional choices but has to search for alternatives, both for low and high permittivity replacements. In this article we survey currently used low dielectric constant materials and future trends for microelectronic applications.     

含空位缺陷碳化硅纳米管的电子结构和光学性质

Based on first-principle calculations,the electronic structures and optical properties of a single-walled (7,0) SiC nanotube(SiCNT) with a carbon vacancy defect or a silicon vacancy defect are investigated.In the three silicon atoms around the carbon vacancy,two atoms form a stable bond and the other is a dangling bond.A similar structure is found in the nanotube with a silicon vacancy.A carbon vacancy results in a defect level near the top of the valence band,while a silicon vacancy leads to the formation of three defect levels in the band gap of the nanotube.Transitions between defect levels and energy levels near the bottom of the conduction band have a close relationship with the formation of the novel dielectric peaks in the lower energy range of the dielectric function.     

Grain boundary diffusion in columnar structure polycrystalline materials

A simple but rigorous solution for the problem of grain boundary diffusion in columnar structure semi-infinite polycrystalline materials is proposed. The method is advantageous over other known methods in that it can be easily extended to media of finite thickness.     

Millimeter-wave dielectric measurement of materials

It is no longer necessary to use extrapolated microwave dielectric values when designing millimeter-wave components and systems. Very recently, highly accurate millimeter-wave (5- to 1/2-mm) data on complex dielectric permittivity and loss tangent have become available to engineers for a variety of materials such as common ceramics, semiconductors, crystalline, and glass materials. One quasi-optical measurement method has proved to be most accurate and reproducible, namely, dispersive Fourier transform spectroscopy (DFTS) applied to a polarizing interferometer. The openresonator method and the Mach-Zehnder-IMPATT spectrometer will also be described and compared. The fact that the dielectric loss increases with frequency in the millimeter, unlike the microwave, is an important feature of these data. Reliable measurements also reveal that the methods of preparation of nominally identical specimens can change the dielectric losses by a factor of three.     

Molecular basis of the interphase dielectric properties of microelectronic and optoelectronic packaging materials

High frequency microelectronic and optoelectronic device packaging requires the use of substrate and encapsulation materials having a low dielectric constant, low dielectric loss and high volume resistivity. Most packaging materials are polymer-ceramic composites. A clear understanding of the broadband dielectric properties of composite materials is thus of great current importance for the effective development of high frequency packaging materials and optimized package design. Toward this goal, a general framework for understanding the dielectric properties of packaging materials was recently developed in which the dielectric constant of polymer-ceramic composite materials is characterized by the electrical properties of the polymer phase, the filler phase and an interphase region within the composite system. However, for this framework to be a viable tool for tailoring the dielectric properties of packaging materials, one must understand the dielectric properties of the polymer-filler interphase region, which represents a region of polymer surrounding and bonded to the surface of each filler particle having unique dielectric and physical characteristics. This work presents a model to explain and predict the dielectric properties of the composite interphase region based on dipole polarization theory.     

Dielectric properties of polycrystalline ZnS

The temperature and frequency dependences of the permittivity of polycrystalline zinc sulfide are investigated. The permittivity is calculated from the electronic-structure parameters. It is shown that an increase in the permittivity at frequencies below 10 kHz occurs as a result of space-charge polarization, which is due to the presence of charged dislocations in interlayer and grain boundaries.     

Electronic progress in materials science

Materials such as polymers, superconducting ceramics, and diamond films are likely to shape the electronics industry in the coming decade. Processing technologies for these improved materials will also gain importance.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.     

Mobility,lifetime and diffusion length in polycrystalline materials

Theoretical investigations of the influence of grain size on mobility, lifetime and diffusion length in a polycrystalline material are made. it is found that the variation of diffusion length with grain size can be accounted for if the dependence of mobility and lifetime on grain size are considered. The calculations reasonably represent the experimentally observed variations of diffusion lengths with grain size.     

Electrical properties of fine-grained polycrystalline CdTe

The temperature dependence of conductivity, the photoconductivity, and the hole mobility in fine-grained polycrystalline CdTe have been studied. The results obtained agree well with the concept of charged grain boundaries. The potential barriers at grain boundaries and the way in which these barriers affect the free carrier mobilities have been determined.     

Switching processes and dielectric breakdown in polycrystalline Nb2O5 films

Repetitive resistive switching from the high-to the low-resistance state in thin polycrystalline Nb₂O₅ films was investigated. The switching process, and dielectric breakdown, are associated with four successive conduction states. The thermal activation energy in the first conduction state is 0.35 eV and in the second state is 0.047 eV; in the third and fourth resistance states the temperature coefficient of resistance exhibits metallic behavior. The I-V relationship changes from the Poole-Frenkel mechanism in the first state to space-charge-limited conduction in the second state and a linear relation in the third and fourth states. These and other results indicate that dielectric breakdown occurs through a process of a metallic precipitation increasing in each consecutive state and the formation of a highly conductive filament in the fourth and final state in the dielectric breakdown process. The values of important switching parameters such as the threshold field for switching E_s, holding current and voltage I_h and V_h, switching time τ_s, delay time τ_d and recovery time τ_r are presented. The dependence of the delay time τ_d on the applied voltage and temperature is studied and the relation τ_d∝exp(−k(V/V_s)) is established, with k showing only a slight temperature dependence. Supported by the Office of Naval Research     

Optical properties of polycrystalline zinc selenide

Dependences of the exponent of radiation flux attenuation on the ZnSe grain size and the wave-length are experimentally determined. At a wavelength of 1.1 μm, the minimum and maximum attenuation is observed in crystals with the smallest and largest grain sizes, respectively. A reverse situation arises at a wave-length of 10 μm. It is concluded that the optical radiation at wavelengths of 1.1 and 10 μm is scattered at internal grain defects and mainly at grain boundaries, respectively. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 3, 2004, pp. 322–324. Original Russian Text Copyright ? 2004 by Bryzgalov, Musatov, Buz’ko.