1.1: Introduction

Having investigated the characteristics of extrinsic N-type and P-type materials in the prior chapter, we shall continue by examining what happens when the these two materials are combined into a single device. It is critical to understand that when we combine P- and N-type materials, we do not do so through simple mechanical means. That is, we do not in some way solder, weld, bolt, friction-fit, glue or duct tape one type of material to another. Rather, we must maintain a single piece of mono-crystalline silicon, not a poly-crystalline amalgam of individual pieces. This can be achieved via a diffusion or ion implantation technique that is applied repeatedly to a single piece of silicon crystal. This will leave regions or zones in the crystal that are N-type or Ptype. In fact, it is quite possible to have a region of one type completely embedded within a region of the opposite type as we shall see in later chapters.

By creating a single zone of N material adjacent to a zone of P material, we wind up with the PN junction. The PN junction is arguably the fundamental building block of solid state semiconductor devices. PN junctions can be found in a variety of devices including bipolar junction transistors (BJTs) and junction field effect transistors (JFETs). The most basic device built from the PN junction is the diode. Diodes are designed for a wide variety of uses including rectifying, lighting (LEDs) and photodetection (photodiodes). We shall begin by examining the basic structure and operation of the PN junction. This will include a look at the many different kinds of diodes available. To assist with circuit analysis, a series of simplified models will be created and investigated. We shall use these models to solve a number of example circuits that feature the many diode variations available.