Nearly everything that we use contains semiconductors. From old relics such as "Transistor Radios", to computers, and everything in between, semiconductors make modern human technology operate. Before this book, wikibooks had a number of sources on semiconductors, scattered as stub pages and individual chapters in other books. However, this book is an attempt to bring all that information together into a single resource, and therefore become more valuable to the wikibooks community at large. Now, other books that used to provide their own mini discussions of semiconductors can instead link to this book in an effort to save time and space.
Semiconductors are special materials (frequently silicon-based) that conduct differently under different conditions. This is, of course, only a partial definition, but it is certainly an important part. Semiconductors can be used to control the flow of electricity in a circuit, they can be used to amplify a signal, or they can be used to switch current flow on or off. In fact, this is only a small subset of the things that semiconductors can do. This book will explain what semiconductors are, and how they are used.
It is the intent of this book to become a thorough and complete reference resource on semiconductors. The first section will discuss what semiconductors are, and how they are constructed physically. The second section will begin to discuss transistors, first through the use of specific models (Transistors as a switch, and Transistors as an amplifier). Section 3 will talk about Field Effect Transistors (FET), how they operate, and how they are made. Section 4 will talk further about the use of transistors as amplifiers, and will discuss Op-Amp circuits in detail. Section 5 will discuss rectifier circuits and regulator circuits. Section 6 will talk more in depth about using transistors as switches, and will discuss the popular CMOS and TTL design methodologies. Finally, section 7 will discuss the use of light with semiconductors, including phototransistors, photodiodes, and LEDs. In the future, additional topics may be covered.
|To understand the fundamental concepts of semiconductors, one must apply modern physics to solid materials. More specifically, we are interested in semiconductor crystals. Crystals are solid materials consisting of atoms, which are placed in a highly ordered structure called a lattice. Such a structure yields a periodic potential throughout the material, which results in some remarkable properties. |
|Two properties of crystals are of particular interest, since they are needed to calculate the current in a semiconductor. First, we need to know how many fixed and mobile charges are present in the material. Second, we need to understand the transport of the mobile carriers through the semiconductor.|
|In this chapter we start from the atomic structure of semiconductors and explain the concepts of energy bands, energy band gaps and the density of states in an energy band. We also show how the current in an almost filled band can more easily be analyzed using the concept of holes. Next, we discuss the probability that energy levels within an energy band are occupied. We will use this probability density to find the density of electrons and holes in a band. |
|Two carrier transport mechanisms will be considered. The drift of carriers in an electric field and the diffusion of carriers due to a carrier density gradient will be discussed. Recombination mechanisms and the continuity equations are then combined into the diffusion equation. Finally, we present the drift-diffusion model, which combines all the essential elements discussed in this chapter.|
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