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Semiconductors and doping Semiconductors are materials which are neither conductors or insulators, having conductivities intermediate to those of conductors like copper and insulators like wood or plastic. Common semiconductors are Silicon and Germanium. The reason semiconductors are important is that with some engineering they can sometimes both conduct and insulate depending on their connections. Thus they serve as the basis for switching and amplification, the fundamental actions of computer elements. A typical modern processor has several million transistors, one of the elements manufactured from semiconducting material which we will study here. Doping refers to the addition of impurities to a semiconductor. The addition of impurities adds charge carrying elements to the semiconductor. The two classes of doping are p-type and n-type which refer to the introduction of positive and negative charge carriers. For instance if one introduces a Phosphorus atom into a silicon lattice, the phosphous atom would prefer to shed one of the electrons in its outer shell in order to fit in with the silicon lattice. This electron is then available to slide through the material, carrying current. This is an example of n-type doping. By doping the same lattice with Boron, the Boron site wishes to suck an electron out of the silicon lattice to fit neatly into the structure. The site which is now missing an electron represents a positive charge, and therefore the doping is p-type. Movement of this site constitutes a current. Doping becomes important when p-doped and n-doped materials are connected. This constitutes a diode which is the subject of the next page. |
