The matter and material in nature can be divided into three categories: conductor, semiconductor and insulator according to their conductivity. The resistivity of the semiconductor is in the range of 1m Omega cm ~ 1G Omega cm (the upper limit is taken by Xie Jiakui's "electronic circuit", as well as its 1/10 or 10 times; the current description is temporarily used because of the unavailability of the corner mark). In general, the conductivity of semiconductors decreases with the increase of temperature, which is exactly opposite to that of metal conductors.
All materials with the above two characteristics can be classified as semiconductor materials. Reflecting the intrinsic properties of semiconductor materials is the physical effects and phenomena caused by various external factors acting on semiconductors，such as light, heat, magnetism, electricity and so on.These can be collectively referred to as the semiconductor properties of semiconductor materials. Most of the substrate materials of the solid state electronic devices are semiconductors,and it is these various semiconductor properties of semiconductor materials have special functions and features of different types of semiconductor devices in different. The basic chemical characteristics of semiconductors lie in the existence of saturated covalent bonds between atoms. The typical characteristic of the covalent bond is the tetrahedral structure on the lattice structure, so the typical semiconductor material has the structure of diamond or sphalerite (ZnS). Since the earth's mineral deposits are mostly compounds, the earliest used semiconductor materials are compounds, such as PbS, used early for radio detection, copper oxide (Cu2O) as solid rectifier, sphalerite (ZnS) as a well known solid luminescent material, and the rectifying effect of silicon carbide (SiC) was also used earlier. Selenium (Se) is the first discovered and utilized element semiconductor， It once was an important material for solid rectifiers and photocell. The discovery of elemental semiconductor germanium (Ge) has opened up a new page in the history of semiconductors, and from this time electronic devices began to be transistors. China's semiconductor research and production began in 1957 with the production of high purity (99.999999% to 99.9999999%) germanium for the first time. After the use of elemental semiconductor silicon (Si), it not only increases the type and variety of transistors, but also improves the performance of the transistors. It also ushered in the era of large-scale and ultra large scale integrated circuits. The discovery of III - V compounds represented by gallium arsenide (GaAs) has promoted the rapid development of microwave devices and optoelectronic devices.
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