掺氮6H-SiC单晶的电阻率、迁移率及自由载流子浓度

测试了国产和美国Cree公司生产的n型6H-SiC低温下的电学参数,包括电阻率、迁移率和自由载流子浓度,并用FCCS软件数据拟合分析得到两种SiC的杂质浓度和能级.实验结果表明:杂质浓度和补偿度对低温下SiC的电性能有很大影响,轻度补偿的掺氮6H-SiC是施主氮的两个能级共同起作用;而重度补偿的6H-SiC在低温时则是受主能级起作用,并且后者迁移率随温度变化曲线的峰值降低并右移.同时发现重度补偿的SiC在较低温度时由n型转变成了p型,并从理论上分析了产生这种现象的原因.     

钒掺杂形成半绝缘6H-SiC的补偿机理

研究了钒掺杂生长半绝缘6H-SiC的补偿机理.二次离子质谱分析结果表明,非故意掺杂生长的6H-SiC中,氮是主要的剩余浅施主杂质.通过较深的钒受主能级对氮施主的补偿作用,得到了具有半绝缘特性的SiC材料.借助电子顺磁共振和吸收光谱分析,发现SiC中同时存在中性钒(V4+)和受主态钒(V3+)的电荷态,表明掺入的部分杂质钒通过补偿浅施主杂质氮,形成受主态钒,这与二次离子质谱分析结果相吻合.通过对样品进行吸收光谱和低温光致发光测量,发现钒受主能级在6H-SiC中位于导带下0.62eV处.     

钒掺杂形成半绝缘6H-SiC的补偿机理

研究了钒掺杂生长半绝缘6H-SiC的补偿机理.二次离子质谱分析结果表明,非故意掺杂生长的6H-SiC中,氮是主要的剩余浅施主杂质.通过较深的钒受主能级对氮施主的补偿作用,得到了具有半绝缘特性的SiC材料.借助电子顺磁共振和吸收光谱分析,发现SiC中同时存在中性钒(V4 )和受主态钒(V3 )的电荷态,表明掺入的部分杂质钒通过补偿浅施主杂质氮,形成受主态钒,这与二次离子质谱分析结果相吻合.通过对样品进行吸收光谱和低温光致发光测量,发现钒受主能级在6H-SiC中位于导带下0.62eV处.     

钒受主能级在n型4H-SiC中的深能级瞬态傅里叶谱和光致发光

借助深能级瞬态傅里叶谱研究了钒离子注入在SiC中引入的深能级陷阱.掺人的钒在4H-SiC中形成两个深受主能级,分别位于导带下0.81和1.02eVt处,其电子俘获截面分别为7.0 × 10-16和6.0×10-16cm2.对钒离子注入4H-SiC样品进行低温光致发光测量,同样发现两个电子陷阱,分别位于导带下0.80和1.6eV处.结果表明,在n型4H-SiC掺入杂质钒可以同时形成两个深的钒受主能级,分别位于导带下0.8±0.01和1.1±0.08eV处.     

钒受主能级在n型4H-SiC中的深能级瞬态傅里叶谱和光致发光

借助深能级瞬态傅里叶谱研究了钒离子注入在SiC中引入的深能级陷阱.掺人的钒在4H-SiC中形成两个深受主能级,分别位于导带下0.81和1.02eVt处,其电子俘获截面分别为7.0 × 10-16和6.0×10-16cm2.对钒离子注入4H-SiC样品进行低温光致发光测量,同样发现两个电子陷阱,分别位于导带下0.80和1.6eV处.结果表明,在n型4H-SiC掺入杂质钒可以同时形成两个深的钒受主能级,分别位于导带下0.8±0.01和1.1±0.08eV处.     

钒注入4H-SiC半绝缘特性的研究

研究了2100keV高能量钒注入4H-SiC制备半绝缘层的方法和特性,注入层的浓度分布用蒙特卡罗分析软件TRIM进行模拟.采用一种台面结构进行I-V测试,发现钒注入层的电阻率与4H-SiC层的初始导电类型有很大关系.常温下,钒注入p型和n型4H-SiC的电阻率分别为1.6×1010和7.6×106Ω·cm.测量了不同退火温度下的电阻率,发现高温退火有利于钒的替位激活和提高电阻率,由于钒扩散的影响1700℃退火使得电阻率略有下降.测量了n型SiC钒注入层在20～140℃时的电阻率,计算出钒受主能级在4H-SiC中的激活能为0.78eV.     

钒注入4H-SiC半绝缘特性的研究

研究了2100keV高能量钒注入4H-SiC制备半绝缘层的方法和特性,注入层的浓度分布用蒙特卡罗分析软件TRIM进行模拟.采用一种台面结构进行I-V测试,发现钒注入层的电阻率与4H-SiC层的初始导电类型有很大关系.常温下,钒注入p型和n型4H-SiC的电阻率分别为1.6×1010和7.6×106Ω·cm.测量了不同退火温度下的电阻率,发现高温退火有利于钒的替位激活和提高电阻率,由于钒扩散的影响1700℃退火使得电阻率略有下降.测量了n型SiC钒注入层在20～140℃时的电阻率,计算出钒受主能级在4H-SiC中的激活能为0.78eV.     

电子辐照下的SiC少子寿命退化模型

从理论上对电子辐照在4H-SiC中引入的缺陷数量和各种缺陷能级进行了分析.结果表明,EH6和EH7缺陷能级在4H-SiC中起着有效复合中心的作用.采用SRH模型来估计电子辐照下4H-SiC的少子寿命,并给出了电子辐照下4H-SiC少子寿命损伤系数的模型.结合具体的测量条件,证明了这个模型是合理的.辐照电子对Si、GaAs和4H-SiC产生的不同影响展示了在高空、高辐照条件下 SiC存在着优势.     

掺氮6H—SiC材料电学性质温度依赖关系测量与分析

测量了７－１０００Ｋ的掺氮６Ｈ－ＳｉＣ材料基本电学性质，用电子性方程对载流子浓度温度倒数关系曲线进行拟合，利用化全物半导体散射机构计算了行 率。数据拟合分析得到样品的掺杂浓度、补偿浓度、杂质激光活能和载波子有效质量。分析结果表明，控制杂质能级和表观杂质激活能由补偿度和杂质浓度决定。掺氮６Ｈ－ＳｉＣ材料预期有０．０８ｅＶ、０．１２ｅＶ两个能级，当补偿杂质浓度大于较小能级浓度时，材料将由较高的能级控制     

n型4H-SiC单晶生长工艺研究

采用PVT法掺氮得到n型4H-SiC体单晶。研究了生长温度、冷却孔直径、掺氮量对晶体结晶质量的影响。实验结果表明:生长温度过低或过高会引入多型;冷却孔过大会使晶体产生较大的热应力,导致晶体开裂;掺入较多的氮使SiC晶格畸变。通过调整温场、优化掺氮工艺,获得了生长n型4H-SiC单晶的工艺条件,生长出结晶质量较好的n型4H-SiC单晶。     

GEMNET: a generalized, shuffle-exchange-based, regular, scalable,modular, multihop, WDM lightwave network

GEMNET is a generalization of shuffle-exchange networks and it can represent a family of network structures (including ShuffleNet and de Bruijn graph) for an arbitrary number of nodes. GEMNET employs a regular interconnection graph with highly desirable properties such as small nodal degree, simple routing, small diameter, and growth capability (viz. scalability). GEMNET can serve as a logical (virtual), packet-switched, multihop topology which can be employed for constructing the next generation of lightwave networks using wavelength-division multiplexing (WDM). Various properties of GEMNET are studied     

Thermodynamics of copper matte converting: Part III. Steady-state volatilization of Au,Ag, Pb,Zn, Ni,Se, Te,Bi, Sb,and As from slag,matte, and metallic copper

A comprehensive compilation of various thermodynamic data required for a complete analysis of copper matte converting reactions is presented. The data comprise estimated free energies of formation for such gases as SeO, SeS, TeO, TeS, BiO, BiS, SbO, SbS, AsO, and AsS, as well as activity coefficients in dilute copper alloys and vapor pressures of various elements and compounds. The volatilization of minor elements in steady-state reactors comprising gas and several condensed phases is mathematically formulated, and a parameter which governs the volatilization in such reactors is defined and named volatilization constant. The vapor pressures of various volatile species are calculated thermodynamically for the Noranda Process reactor by assuming equilibrium conditions. The volatilization constants of various minor elements are expressed explicitly as functions of oxygen and sulfur activities. Formerly Associate Professor, Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT     

Bits, symbols, bauds, and bandwidth

The use of clear, concise, and unambiguous language in telecommunications engineering is vital to communicate a desired meaning and understanding. Terminology should be based on rigorous engineering principles and traceable to well known and dependable sources. This article deals with four everyday terms commonly encountered in the popular semi-technical press as well as in serious engineering periodicals. The misuse of these and other terms can lead to low-balled cost proposals, court litigation, and patent infringement cases. Imagine how an engineering student can be confused when she/he typically encounters bandwidth measured in bits per second     

Novel planar, square-shaped, dielectric-waveguide, single-, and dual-mode filters

This paper presents a novel concept of a square-shaped dielectric-waveguide resonator, which can easily realize a dielectric-waveguide cross-coupled filter or a dielectric-waveguide dual-mode filter, using the conventional printed circuit board (PCB) process. This planar dielectric-waveguide resonator has a higher Q value than a microstrip resonator. The physical mechanisms of both single- and dual-mode filters are elucidated. Some new coupling structures are developed for undergoing the PCB process. Filter design procedures are detailed. Design curves for the coupling coefficients of internal- and external-coupling structures are determined by full-wave finite-element-method electromagnetic calculations. Measurement results are highly consistent with theory for all trial filters. This study offers an effective means of producing low-cost high-performance planar circuit filters.     

Uncertainty, Value, Communication, and Problematic Integration

This essay discusses problematic integration (PI) theory, a general perspective on the nature of the dynamic relationship between communication and tensions among expectations and desires and considers the relevance and potential value of PI theory to questions foundational to the field of communication research. The paper begins with a discussion of the main propositions of PI theory, then considers the relationship between the theory and emerging analyses of uncertainty, attending in particular to the meanings of uncertainty and the tensions among uncertainties, wants, and wishes.