1,Specialized English,电子科学与技术专业英语 ,2,电子科学与技术专业英语 ,Semiconductor Materials 1.1 Energy Bands and Carrier Concentration 1.1.1 Semiconductor Materials Solid-state materials can be grouped into three classesinsulators(绝缘体）, semiconductors, and conductors. Figure 1-1 shows the electrical conductivities (and the corresponding resistivities 1/)associated with(相关） some important materials in each of three classes. Insulators such as fused（熔融） quartz and glass have very low conductivities, in the order of 1E-18 to 1E-8 S/cm;,固态材料可分为三种：绝缘体、半导体和导体。图11 给出了在三种材料中一些重要材料相关的电阻值（相应电导率1/)。绝缘体如熔融石英和玻璃具有很低电导率，在10-18 到10-8 S/cm;,3,电子科学与技术专业英语 ,导体如铝和银有高的电导率，典型值从104到106S/cm;而半导体具有的电导率介乎于两者之间。半导体的电导率一般对温度、光照、磁场和小的杂质原子非常敏感。在电导率上的敏感变化使得半导体材料称为在电学应用上为最重要的材料。,and conductors such as aluminum and silver have high conductivities, typically from 104 to 106 S/cm. Semiconductors have conductivities between those of insulators and those of conductors. The conductivity of a semiconductor is generally sensitive to temperature, illumination（照射） , magnetic field, and minute amount of impurity atoms. This sensitivity in conductivity makes the semiconductor one of the most important materials for electronic applications.,5,电子科学与技术专业英语 ,6,Prior to the invention of the bipolar transistor（双极二极管） in 1947,semiconductors were used only as two-terminal（电极） devices, such as rectifiers（整流器） and photodiodes（光敏二极管）. In the early 1950s, germanium was the major semiconductor material.,电子科学与技术专业英语 ,在1947年双极晶体管发明之前，半导体仅用作双极型器件如整流器和光敏二极管。早在20世纪50年代，锗是主要的半导体材料。,7,However, germanium proved unsuitable in many applications because germanium devices exhibited high leakage currents（漏电流） at only moderately elevated temperatures. In addition, germanium oxide is water soluble and unsuited for device fabrication. Since the early 1960s silicon has become a practical substitute（实际取代） and has now virtually supplanted（事实上替代） germanium as a material for semiconductor fabrication(结构）,电子科学与技术专业英语 ,然而锗不太适合在很多方面应用因为温度适当提高后锗器件会产生高的漏电流。另外，锗的氧化物是水溶性的不适合器件制作。所以20世纪60年代实际上锗被硅所取代，事实上硅替代锗成为半导体制作的材料之一。,8,The main reasons we now use silicon are that silicon devices exhibit much lower leakage currents, and high-quality silicon dioxide can be grown thermally. There is also an economic consideration. Device grade silicon costs much less than any other semiconductor material. silicon in the form of silica and silicates（硅酸盐） comprises 25% of the Earths crust（地表）, and silicon is second only to oxygen in abundance（分布）. At present, silicon is one of the most studied elements in the periodic table; and silicon technology is by far the most advanced among all semiconductor technologies.,电子科学与技术专业英语 ,我们用硅材料的主要原因有硅器件存在非常低的漏电流且能够通过热法生长出高质量的二氧化硅。器件级硅成本远少于其它半导体材料。硅以硅石和硅酸盐形式存在并占地球地表层的25，而且硅元素在分布中排在氧之后的第二位。当今硅是在元素周期表中研究最多的元素；硅技术是在所有半导体技术中最先进的。,9,Many of the compound semiconductors have electrical and optical properties that are absent（缺少） in silicon. These semiconductors, especially gallium arsenide (GaAs), are use mainly for microwave and photonic applications. Although we do not know as much about the technology of compound semiconductor as we do about that of silicon, compound semiconductor technology has advanced partly because of the advances in silicon technology. In this book we are concerned mainly with device physics and processing technology of silicon and gallium arsenide.,电子科学与技术专业英语 ,有很多化合物半导体具有硅所缺少的电光性能。这些半导体特别是GaAs主要用作微波和光学应用。虽然我们了解化合物半导体技术不如硅材料的多，但化合物半导体技术由于硅技术的发展而发展。在本书中我们主要介绍硅和砷化镓的器件物理和制备技术。，,10,Crystal Structure The semiconductor materials we will study are single crystals, that is, the atoms are arranged in a three-dimensional periodic fashion. The periodic arrangement（排布） of atoms in a crystal is called a lattice（晶格）. In a crystal, an atom never stray（偏离） far from a single, fixed position. The thermal vibrations associated with the atom are centered about this position. For a given semiconductor, there is a unit cell（晶胞） that is representative of the entire lattice; by repeating the unit cell throughout the crystal, one can generate the entire lattice.,电子科学与技术专业英语 ,我们研究的半导体材料是单晶，也就是说，原子是按照三维周期形式排列。在晶体中原子的周期排列称为晶格。在晶体里，一个原子从不远离它确定位置。与原子相关的热运动也是围绕在其位置附近。对于给定的半导体，存在代表整个晶格的晶胞，通过在晶体中重复晶胞组成晶格。,11,Figure 1-2 shows some basic cubic-crystal unit cells. Figure 1-2(a) shows a simple cubic（立方） crystal; each corner of the cubic lattice is occupied by an atom that has six equidistant（等距） nearest neighboring atoms. The dimension a is called the lattice constant. Only polonium（钋） is crystallized in the simple cubic lattice. Figure 1-2(b) is a body-centered cubic（体心立方） (bcc) crystal, where in addition to the eight corner atoms, an atom is located at center of the cube.,电子科学与技术专业英语 ,图12给出一些立方晶体晶胞。图12（a）给出了一个简单的立方晶体；立方晶格的每个角由一个原子占据，所以有6个等距原子。a的大小称为晶格常数。只有金属钋明确是单立方晶体。图12（b）是体心立方晶体，除了8个角原子外，一个原子在其立方中心上。,12,In a bcc lattice, each atom has eight nearest-neighboring atoms. Crystals exhibiting bcc lattices include those of sodium（钨） and tungsten（钠）. Figure 1-2(c)shows a face-centered cubic (fcc) （面心立方）