Silicon semiconducting properties

Semiconductors may also be made from a maferial which is normally an insulator by infroducing an impurify, a process known as doping. Figure 9.9 shows fwo ways in which an impurify may promote semiconducting properties. In Figure 9.9(a) fhe dopanf has one more valence election per atom fhan fhe hosf and confribufes a band of filled impurify levels 1 close to fhe conduction band of fhe hosf. This characterizes an n-fype semiconductor. An example is silicon (KL3s 3p ) doped wifh phosphoms (KL3s 3p ), which reduces fhe band gap to abouf 0.05 eY Since kT af room femperafure is abouf 0.025 eY the phosphoms... 

Polysilanes can be regarded as one-dimensional analogues to elemental silicon, on which nearly all of modern electronics is based. They have enormous potential for technological uses [1-3]. Nonlinear optical and semiconductive properties, such as high hole mobility, photoconductivity, and electrical conductivity, have been investigated in some detail. However, their most important commercial use, at present, is as precursors to silicon carbide ceramics, an application which takes no advantage of their electronic properties. 

The crystal structure of germanium is similar to that of diamonds and sihcon, and its semiconducting properties are also similar to silicon. 

Semiconducting Properties. Silicon carbide is a semiconductor it has a conductivity between that of metals and insulators or dielectrics (4,13,46,47). Because of the thermal stability of its electronic structure, silicon carbide has been studied for uses at high (>500° C) temperature. The Hall mobility in silicon carbide is a function of polytype (48,49), temperature (41,42,45—50), impurity, and concentration (49). In n-type crystals, activation energy for ionization of nitrogen impurity varies with polytype (50,51). 

The theory outlined above was developed for group IY semiconducting elements such as silicon and germanium some of the compounds of group III and Y elements, the III-V compounds, are also covalently bonded and have similar electrical properties which can be described in terms of a band model. The best known semiconducting III-V compound is GaAs, which is exploited for both its photonic and semiconducting properties. 

The alternatives to metal-based semiconductors are organic semiconductors, but they struggle to reach efficiencies of 5%, although there are hints in the scientific literature of polymers that are comparable to silicon in their semiconducting properties. Even so, polymers rely on double bonds along the backbone of the polymer to provide the structure along which electrons and holes can move, but double bonds are always susceptible to oxidation by the oxygen of the atmosphere so they have to be protected. 

Silicon s most familiar use is in the production of microprocessor chips. Computer microprocessor chips are made from thin slices, or wafers, of a pure silicon crystal. The wafers are doped with elements such as boron, phosphorus, and arsenic to confer semiconducting properties on the silicon. A photographic process places patterns for several chips onto one wafer. Gaseous compounds of metals are allowed to diffuse into the open spots in the pattern, and then the pattern is removed. This process is repeated several times to build up complex microdevices on the surface of the wafer. When the wafer is finished and tested, it is cut into individual chips. 

Explain why you would expect germanium to have the same type of structure and semiconducting properties as silicon. 

Silicon only exhibits semiconducting properties when ultrapure. 

Elemental silicon is used to make silicone polymers. Its semiconducting properties (Section 13-17) are used in transistors and solar cells. 

Metalloids have some chemical and physical properties of metals and other properties of nonmetals. In the periodic table, the metalloids lie along the border between metals and nonmetals. Silicon (Si) is probably the most well-known metalloid. Some metalloids such as silicon, germanium (Ge), and arsenic (As) are semiconductors. A semiconductor is an element that does not conduct electricity as well as a metal, but does conduct slightly better than a nonmetal. The ability of a semiconductor to conduct an electrical current can be increased by adding a small amount of certain other elements. Silicon s semiconducting properties made the computer revolution possible. 

The elements that fall into this category are silicon, germanium, selenium and tellurium. Iodine shows some semiconducting properties, and phosphorus, sulfur and arsenic can each be obtained in a crystalline form that has the properties of a semiconductor, although this is not the most stable form of these elements under normal conditions. 

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