Controlling the Conductivity of Semiconductors

Silicon can also be doped with a group 3A element, such as gallium, which has only three valence electrons. When gallium is incorporated into the silicon crystal structure, it results in electron holes, or empty molecular orbitals, in the valence band. The presence of holes also allows for the movement of electrical current because electrons in the valence band can move between holes. In this way, the holes move in the opposite direction as the electrons. This type of semiconductor is called a p-type semiconductor because each hole acts as a positive charge. 

The heart of most modem electronic devices are silicon chips containing millions of p-n junctions, tiny spots that are p-type on one side and n-type on the other. These junctions can serve a number of functions including acting as diodes (circuit elements that allow the flow of electrical current in only one direction) or amplifiers (elements that amplify a small electrical current into a larger one). 

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Understand how n-type and p-type doping can be used to control the conductivity of semiconductors. [Section 12.7]... 

Many of the elements that lie along the zigzag diagonal hne that divides metals and nonmetals are metalloids and exhibit mixed properties. Several metalloids are also classified as semiconductors because of their intermediate (and highly temperature-dependent) electrical conductivity. Our ability to change and control the conductivity of semiconductors makes them useful to us in the manufacture of the electronic chips and circuits central to computers, cellular telephones, and many other modem devices. Good examples of metalloids include sihcon, arsenic, and antimony. 

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