OVERVIEW OF ELECTRONIC DEVICES

This Chapter reviews some of the basic physics and operation of selected circuit elements used in microelectronic devices. For a complete review, see the suggested readings. Basic resistance, capacitance, and inductance were covered in Chapter 2. We focus here on diodes, including clas-sic homojunctions, heterojunctions, and Schottky barriers, because they illustrate most of the important issues in microelectronic materials and because both field-effect and bipolar junction transistors are constructed from them. Once we have discussed diodes, a brief review of these two major classes of transistors is provided. Finally, we finish the review with some of the issues unique to light emitting and laser diodes. 

The terms homojunction and heterojunction are used frequently in this chapter. A homojunction is a contact between two of the same semiconductors (silicon with sdicon for example) while a heterojunction is a contact between two dissimilar materials. Heterojunctions, see Sections 3.3-3.4, can include a semiconductor with a semiconductor (Si with Ge for example) or semiconductors with metals (Ni with GaAs for example). 

Diodes (solid state devices rather than vacuum tubes) can be any of these jxmction types and have the property that they pass current easily in only one direction. Understanding diodes requires knowledge of how charges move when jrmctions are formed and how contact potentials are created. Thus, one must first understand the movement of carriers in solids in response to electric fields or chemical concentration gradients. These motions are typically divided into two categories, diffusion driven by concentration gradients and drift - motion resulting from electric fields. 

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