——电材专业英语课文翻译
Semiconductor Materials
? 1.1 Energy Bands and Carrier Concentration
? 1.1.1 Semiconductor Materials
? Solid-state materials can be grouped into three classes—insulators(绝缘体）, semiconductors, and conductors. Figure 1-1 shows the electrical conductivities δ (and the corresponding resistivities ρ≡1/δ)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1－1 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ρ≡1/δ)。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;
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.
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。
The study of semiconductor materials began in early nineteenth century. Over the years many semiconductors have been investigated. Table 1 show a portion（部分) of the periodic(周期） table related to semiconductors. The element semiconductors, those composed of single species of atoms, such as silicon (Si) and germanium (Ge), can be found in Column Ⅳ. However, numerous compound semiconductors are composed of two or more elements. For example, gallium arsenide (GaAs) is a Ⅲ-Ⅴ compound that is a combination（合成） of gallium (Ga) from Column Ⅲ and arsenic (As) from Column Ⅴ.
早在19世纪人们已经开始研究半导体材料。多年来人们研究了很多半导体材料。表1给出了与半导体相关的周期表中的部分元素。由单种元素组成的单质半导体如硅和锗在第Ⅳ族。而大量的化合物半导体有两个甚至更多元素组成。如GaAs是Ⅲ-Ⅴ化合物是由Ⅲ族的Ga和Ⅴ族的As化合而得。
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.
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。
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）
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。
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 Earth’s 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
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。
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.
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。
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 singl
e, 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.
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。
??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.
图1－2给出一些立方晶体晶胞。图1－2（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1－2（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。
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）crystal that has one atom at each of the six cubic faces in addition to（还有） the eight corner atoms. In an fcc lattice, each atom has 12 nearest neighboring atoms. A large number of elements exhibit the fcc lattice form, including aluminum, copper, gold, and platinum（铂）.
在体心立方晶格中，每个原子具有8 个相近原子。呈bcc晶格的晶体包括钨和钠晶体。图1－2（c）给出了面心立方晶体除了8个角原子外六个立方面上还有一个原子。在fcc晶格中每个原子有12 相邻原子。大量的元素是fcc晶格形式，包括铝、铜、金和铂。
The element semiconductors, silicon and germanium, have a diamond lattice structure（金刚石晶体结构）. This structure also belongs to the cubic-crystal family and can be seen as two interpenetrating（渗透） fcc sublattices(亚点阵） with one sublattice displaced（移动） from the other by one quarter of the distance along a diagonal（对角线） of the cube (i.e.,a displacement（位移） of a ).
元素半导体如硅和锗具有金刚石晶体结构。这种结构属于金刚石结构并且视为两个互相贯穿的fcc亚点阵结构，这个结构具有一个可以从其它沿立方对
角线距离的四分之一处移动的子晶格（位移 。）
All atoms are identical in a diamond lattice, and each atom in the diamond lattice is surrounded by four equidistant（等距） nearest neighbors that lie at the corners of a tetrahedron（四面体）. Most of the Ⅲ-Ⅴ compound semiconductors (e.g.,GaAs) have a zincblende（闪锌矿） lattice, which is identical（相同） to a diamond lattice except that one fcc sublattice has column Ⅲ atoms (Ga) and the other has Column Ⅴatoms (As).
在金刚石晶体所有原子都相同，且在金刚石晶体都有在四面体角上的四个等距相近原子所包围。多数每个原子Ⅲ-Ⅴ 化合物半导体具有闪锌矿结构，它有金刚石相同结构除了一个fcc子晶格结构有一个Ⅲ 族原子Ga和 Ⅴ族原子 As。
? Therefore, the crystal properties along different planes are different, and the electrical and other device characteristic are dependent on the crystal orientation. A convenient method of defining the various planes in a crystal is to use Miller indices（密勒指数）.
因此，不同面的晶体特性也不同，且电和其它器件特性依赖于晶体取向。一种常用定义在晶体中不同晶面的方法是用密勒指数。
Valence Bonds （价键）
As discussed in Section 1.1.2, each atom in a diamond lattice is surrounded by four nearest neighbors. Each atom has four electrons in the out orbit（轨道）, and each atom shares these valence electrons（价电子） with its neighbors. This sharing of electrons is known as covalent bonding（共价键）; each electron pair（电子对） constitutes a covalent bond. Covalent bonding occurs between atoms of the same element, or between atoms of different elements that have similar outer-shell electron configurations（结构）. Each electron spends an equal amount of time with each nucleus.
?如1.1.2节所述，在金刚石结构的每个原子被4个相邻原子所包围。每个原子在外轨道具有4个电子，并且每个电子与相邻原子共享价电子；每对电子组成一个共价键。共价键存在于同种原子之间或具有相同外层电子机构的不同元素的原子间。每个电子与每个原子核达到平衡需要相同时间。
However, both electrons spend most of their time between the two nuclei. The force of attraction（吸引力） for the electrons by both nuclei holds the two atoms together. For a Zincblende lattice（闪锌矿） such as gallium arsenide, the major bonding force is from the covalent bonds. However, gallium arsenide has a slight（少） ionic bonding force that is an electrostatic（静电引力） attractive force between each Ga+ ion and Its four neighboring As- ions, or between each As- ion and Its four neighboring Ga+ ions.
然而，所有电子需要很多时间在两个原子核间达到平衡。两个原子核对电子的吸引力保证两个原子在一起。对于闪锌矿结构如砷
化镓主要的价键引力主要来自于共价键。当然，砷化镓也具有小的离子键引力即Ga+离子与四周 As-离子,或 As- 离子和四周 Ga+ 离子.
At low temperatures, the electrons are bound（束缚） in their respective（各自） tetrahedron（四面体） lattice; consequently, they are not available for conduction. At higher temperatures, thermal vibrations may break the covalent bonds. When a bond is broken, a free electron results that can participate（参与） in current conduction. An electron deficiency（空位） is left in the covalent bond. This deficiency may be filled by one of the neighboring electrons, which results in a shift of the deficiency location, as from location A to location B . We may therefore consider this deficiency as a particle similar to an electron. This fictitious（假想） particle is called a hole.
在低温下，电子束缚在它们各自四面体晶格中；从而不能用来导电。当一个价键断开，一个自由电子能参与电路导电。一个电子空位留在共价键中。这个空位被相邻电子填充导致空位移动，如A到B位置。我们可以空位认同于与电子相同的粒子。这个假想粒子称为空穴。
It carries a positive charge and moves, under the influence of an applied electric field, in the direction opposite to that of an electron. the concept of a hole is analogous（类似） to that of an electron. The concept of a hole is analogous to that of a bubble（泡沫） in a liquid. Although it is actually the liquid that moves, it is much easier to talk about the motion（移动） of the bubble in the opposite direction.
它带有正电荷在外加电场下，沿着电子运动方向相反地方移动。空穴的概念类似电子的概念。空穴的概念类似于液体中泡沫的定义。虽然它的确可与液体流动，这很容易想到泡沫移动是向相反方向。
Energy Bands
For an isolated (孤立）atom, the electrons of the atom can have only discrete（不连续） energy levels. For example, the energy levels for an isolated hydrogen atom are given by the bohr model
?对于孤立原子，原子的电子有不连续的能级。如，孤立氢原子的能级可由玻尔模型得出：
Where m0 is the free-electron mass, q is the electronic charge,ε0is the free-space permittivity （电导率）, h is the plank constant, and n is a positive integer（整数） called the principal quantum（量子） number. The discrete energies are -13.6eV for the ground level (n=1), -3.4eV for the first excited (n=2),etc.
?式中m0 代表自由电子质量, q是电荷量,ε0是真空中电导率, h 是普朗克常数， n 是正整数称为主量子数。不连续能量在基态为 -13.6eV (n=1), 第一激发态为-3.4eV (n=2),etc.
We now consider two identical（相同） atoms. When they are far apart（远离）, the allowed energy levels for a given principal quantum number (e.g., n=1)consist
of one doubly degenerate（双重简并） level, that is, each atom has exactly then same energy (e.g., -13.6eV for n=1). As the two atoms approach one another, the doubly degenerate energy level will spilt into two levels by the interaction （相互作用）between the atoms. When we bring N atoms together to form a crystal, the N-fold degenerate energy level will split into N separate but closely spaced levels due to atomic interaction.
我们考虑两个相同原子.当它们 远离时, 对所给主量子数 (e.g., n=1)的允态能级具有双重简并能级,也就是说，每个原子具有相同能级 (e.g., -13.6eV for n=1).当两个原子相互靠近，这个双重简并能级将被原子间相互作用分成两个能级。当从晶体中引入N个原子，N重简并能级将会分成N个能级，但原子相互作用能级相互接近。
This results in an essentially（基本） continuous band of energy.
The detailed energy band structures of crystalline solids have been calculated using quantum mechanics(量子理论）. Figure 1-3 is a schematic diagram of the formation of a diamond lattice crystal from isolated（孤立） silicon atoms. Each isolated atom has its discrete（不连续） energy levels (two levels are shown on the far right of the diagram). As the interatomic（原子间） spacing decreases, each degenerate energy level splits to form a band.
这导致一个基本连续的能带。结晶固体的详细能带结构能够用量子理论计算而得。图1－3是孤立硅原子的金刚石结构晶体形成的原理图。每个孤立原子有不连续能带（在右图给出的两个能级）。如原子间隔的减少，每个简并能级将分裂产生带。
Further decrease in spacing causes the bands originating（引起） from different discrete levels to lose their identities（同性） and merge（合并） together, forming a single band. When the distance between atoms approaches the equilibrium interatomic spacing of the diamond lattice (with a lattice constant of 0.543 nm for silicon), this band splits again into two bands.
在空间更多减少将导致能带从不连续能级到失去其特性并合并起来，产生一个简单的带。当原子间距离接近金刚石结构的平衡原子间距（对硅而言晶格常数0.543 nm ），这个带分为两个带区。
These bands are separated by a region which designates（指明） energies that the electrons in the solid cannot possess. This region is called the forbidden gap, or bandgap（带隙） Eg. The upper band is called the conduction band（导带）, while the lower band is called valence band（价带）, as shown on the far left of Figure 1-3.
?这些带被固态电子不能够拥有的能量区域分开。这个区域称为禁带或带隙Eg。如图1－3左侧所示上面称为导带下面称为价带。
Figure1-4 shows the energy band diagrams of three classes of solids –insulators, semiconductors, and conductors.
In an insulator such as silicon dioxide (SiO2), the valence electrons form strong bonds between neighboring atoms. These bonds are difficult to break, and consequently（因此） there are no free electrons to participate（产生） in current conduction.
?图1－4给出了三种固体（绝缘体、半导体、导体）的能带图。在绝缘体（如SiO2), 价电子在相邻原子间产生强的价键。这些键很难断开，因此没有自由电子在电流传导过程中产生。
As shown in the energy band diagram Figure1-4(a), there is a large bandgap（带隙）. Note that all energy levels in the valence band are occupied（填充） by electrons and all energy levels in the conduction band are empty. Thermal energy or an applied electric field（外加电场） cannot raise the uppermost electron in the valence band to the conduction band. Therefore, silicon dioxide is an insulator, which cannot conduct current..
?如图1－4（a）能带图所示，有一个大带隙。注意到所有的价带都被电子充满而导带中能级是空的。热能量和外加电场不能够提高在价带中最上层电子到导带。因此，二氧化硅是绝缘体不能导电。
As we discussed in section 1.1.3, bonds between neighboring atoms in a semiconductor are only moderately（适中） strong. Therefore, thermal vibrations（振动） will break some bonds. When a bond is broken, a free electron along with a free hole result. Figure 1-4(b) shows that the bandgap of a semiconductor is not as large as that of an insulator (e.g., Si with a bandgap of 1.12eV).
?如1.1.3节所述，在半导体中相邻原子价键仅仅一定程度强。因此，热振动将断开其中的价键。当价键断开后，产生了自由电子连同自由空穴。图1－4（c）给出的半导体的带隙不如绝缘体宽。（如硅带隙1.12eV）
Because of this ,some electrons will be able to move from the valence band to the conduction band, leaving holes in the Valence band .when An electric field is applied, both the electrons in the conduction band and the holes in the valence band will gain kinetic energy（动能） and conduct electricity.
?正因为此，一些电子能够从价带移动到导带，在在价带中留下空穴。当外加电场后，所有在导带中电子和在价带中的空穴将得到动能并能够导电。
In conductors such as metals, Figure 1-4(c),the conduction band either is partially（部分） filled or overlaps（重叠） the valence band so that there is no bandgap. As a consequence（结果）, the uppermost electrons in the partially filled band or electrons at the top of the valence band can move to the next-higher available energy level when they gain kinetic energy (e.g., from an applied electric field（外加电场）). therefore, current conduction can readily occur in conductors.
在导体中如金属，图1－4（c)所示，导带不是部分填充即使与价带重叠以至于没有带隙结果
，半满带的最上层电子以及价带顶部电子在获得动能（外加电场）可以运动到与其相应的其它较高能级。因此，电流很容易在导体中产生。
The energy band diagrams shown in Figure 1-4 indicate（说明） electron energies. When the energy of an electron is increased, the electron moves to a higher position in the band diagram. On the other hand, when the energy of a hole is increased, the hole moves downward in the valence band. (This is because a hole has a charge opposite that of an electron.)
如图1－4能带图说明了电子能量。当电子能量增加，电子将移动到带图中高的位置。相反，当空穴能量增加，空穴将移动到价带的低位置。（这是因为空穴带电量与电子相反）
As we discussed before, the separation （间距）between the energy of the lowest conduction band and that of the highest valence is called the bandgap Eg, which is the most important parameter（参数） in semiconductor physics. We designate（设定） Ec as bottom of the conduction band; Ec corresponds to the potential energy of an electron, that is, the energy of a conduction electron that is at rest.
正如以前讨论过，最高价带能量与最低导带能量之间间距称为带隙，带隙是半导体物理中最重要的参数。我们设Ec为导带的底端；Ec与电子势能相关，也就是，静止时导电电子的能量。
the kinetic energy of an electron is measured upward from Ec. Similarly ,we designate Ev as top of the Valence band; Ev corresponds to the potential energy（势能） of a hole. the kinetic energy of a hole is measured downward from Ev.
At room temperature and under normal atmosphere, the value of the bandgap are 1.12ev for silicon and 1.42ev for gallium arsenide. The bandgap approaches 1.17ev for silicon and 1.52 ev for gallium arsenide at 0 K.
一个电子的动能可以从Ec上端测得。同样，我们设Ev为价带的上端值；Ev与空穴的势能相关。空穴的动能可从Ev下端值测得。
在室温和标准大气压下，带隙值硅（ 1.12ev ）砷化镓（1.42ev）在0 K带隙研究值硅（ 1.17ev ）砷化镓（1.52ev）
1.1.5 Density of States
当电子在半导体材料中沿着x方向前后运动时，其运动可以用驻波来描述.驻波波长和半导体的长度的关系是:
? nx是一个整数.波长可以表示为）
? h是普朗克常数， px是晶体在x方向的动量。把方程1-2代入方程1-1得到
? 每增加1，动量的增量是
? 对边长为L的三维立方体，有:
? 对L=1的单位立方体，动量空间中的体积于是等于h3.n变化产生一组整数(nx,ny,nz),每组整数(nx,ny,nz)相应于一个允许的能态.
? 所以对于能态的动量空间的大小为h3,从p到p+dp的两个同心球之间的体积是4πp2dp （此体积中包含的能态数是2(4πp2dp)/h3 ，这里因子2计入了电子自旋。用E代替p 得到.
N(E)叫做状态密度
，就是每单位体积允许的能态密度。