Chapter Doping

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • DopingFor a semiconductor material to have the properties needed to work in electronic com-ponents, impurities are usually added. The impurities cause the material to conductcurrents in certain ways. The addition of an impurity to a semiconductor is called dop-ing. Sometimes the impurity is called a dopant.Donor impuritiesWhen an impurity contains an excess of electrons, the dopant is called a donor impu-rity. Adding such a substance causes conduction mainly by means of electron flow, asin a metal like copper. The excess electrons are passed from atom to atom when a volt-age exists across the material. Elements that serve as donor impurities include anti-mony, arsenic, bismuth, and phosphorus.A material with a donor impurity is called an N type semiconductor, because elec-trons have negative charge.Acceptor impuritiesIf an impurity has a deficiency of electrons, the dopant is called an acceptor impurity.When a substance such as aluminum, boron, gallium, or indium is added to a semicon-ductor, the material conducts by means of hole flow. A hole is a missing electron; it isdescribed in more detail shortly.A material with an acceptor impurity is called a P-type semiconductor, becauseholes have positive charge.Majority and minority charge carriersCharge carriers in semiconductor materials are either electrons, which have a unit neg-ative charge, or holes, having a unit positive charge. In any semiconductor material,some of the current is in the form of electrons passed from atom to atom in a nega-tive-to-positive direction. Some current occurs as holes that move from atom to atom ina positive-to-negative direction.Sometimes electrons dominate the current flow in a semiconductor; this is the caseif the material has donor impurities. In substances having acceptor impurities, holesdominate. The dominating charge carriers (either electrons or holes) are the majoritycarriers. The less abundant ones are the minority carriers.The ratio of majority to minority carriers can vary, depending on the nature of thesemiconducting material.Electron flowIn an N-type semiconductor, most of the current flows as electrons passed from atom to atom. But some of the current in a P-type material also takes this form. You learned about 362 Introduction to semiconductors