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1、无 锡 职 业 技 术 学 院毕业设计说明书（英文翻译）Semiconductors1 Semiconductors Fundamentals1.1 Semiconductors MaterialsSolid-state materials can be grouped into three classesinsulators, semiconductors and conductors. Insulators such as fused quartz and glass have very low conductivities. Semiconductors have conductivit
2、ies, typically between those of insulators and those of conductors. The conductivity of a semiconductor is generally sensitive to temperature, illumination, magnetic field, and minute amount of impurity atoms. This sensitivity in conductivity makes the semiconductor one of most important materials f
3、or electronic application.The study of semiconductor materials began in the early nineteenth century. Over the years many semiconductors have been investigated. The element semiconductors, those composed of single species of atoms, such as silicon (Si) and germanium (Ge)can be found in Column 4.howe
4、ver, numerous compound semiconductors are composed of two or more elements. For example, gallium arsenide (GaAs) is an 3-5 compound that is a combination of gallium (Ga) from Column 3 and arsenic (As) from Column 5.Prior to the invention of the bipolar in 1947, semiconductors were used only as two-t
5、erminal devices, such as rectifiers and photodiodes. In the early 1950s, germanium was the major semiconductor material. However, germanium proved unsuitable in many applications because germanium devices exhibited high leakage currents at only moderately elevated temperatures. In addition, germaniu
6、m oxide is water soluble and unsuited for device fabrication. Since the early 1960s silicon has become a practical substitute and has now virtually supplanted germanium as a material for semiconductor fabrication. The main reasons we now use silicon are that silicon devices exhibit much lower leakag
7、e currents, and high-quality silicon dioxide can be grown thermally. There is also an economic consideration. Silicon in the form of silica and silicates comprises 25% of the Earths crust, and silicon is second only to oxygen in abundance. At present, silicon is one of the most studied elements in t
8、he periodic table; and silicon technology is by far the most advanced among all semiconductor technologies.Many of the compound semiconductors have electrical and optical properties that are absent in silicon. There semiconductors especially gallium arsenide (GaAs) are used mainly for microwave and
9、photonic applications. Although we do not know as much about the technology of compound semiconductors as we do about that of silicon, compound semiconductor technology has partly because of the advances in silicon technology.1.2 Crystal StructureSolids may be classified by structural organization i
10、nto crystalline, polycrystalline, and, amorphous types. An amorphous solid does not have a well-define structure; in fact, it is distinguished by its formlessness. In the past decade, amorphous silicon has received a great deal of attention, primarily due to its application in lowcost solar cells. R
11、ecently, amorphous silicon solar cells with an efficiency of greater than 10 percent have been realized, and lower-efficiency devices are being used in consumer electronics, e. g., hand-held calculators and cameras. Exploratory work is being performed to build amorphous field-effect transistors (FET
12、s) for large-area displays and image sensors. Nevertheless, amorphous semiconductors are not expected to play an important role in microelectronics in the foreseeable future. It shoud be pointed out that silicon dioxide, an extremely important material in semiconductor technology is also an amorphou
13、s solid. However, it is used as an insulator, so its electrical conduction property is not of importance to us.In a polycrystalline solid, there are many small regions, each having a well-organized structure but differing from its neighboring regions. Such a material can be produced inexpensively an
14、d is used extensively in microelectronics, e.g., polycrystalline silicon (Poly-Si),which is used as a conductor , contact, or gate in transistors. Both amorphous and polycrystalline materials are structurally more complex, resulting in less well-defined device physics.1.3 Valence Bonds Model of Soli
15、dIn a crystal lattice, a positively charged nucleus is surrounded by negatively charged orbiting electrons in each constituent atom. If the atoms are closely packed, the orbits of the outer-shell electrons will overlap to produce strong interatomic forces. The outer electrons, i.e., valence electron
16、s, are of primary importance in determining the electrical properties of the solid. In a metallic conductor such as aluminum or gold, the valence electrons are shared by all the atoms in the solid. These electrons are not bound to individual atoms and are free to contribute to the conduction of current upon the application of an electric field. The free-electron density of a metallic conductor is on the order of 10 23 cm-3, and the resulting resistivity is sma
