Semiconductor Basics

7Diode Applications

OBJECTIVES OF THIS CHAPTER

In Chapter 5 I covered the simplest, most basic device we can make by combining an n‐type semiconductor with a p‐type semiconductor. The pn‐junction allows current to flow in just one direction. That, by definition, is what a diode does. This property is extremely useful. So now that we know how the pn‐junction works and the electrical properties of the passive elements, resistors, inductors, and capacitors, we are ready to discuss the large number of very useful applications of diodes, from solar cells to rectifiers to a variety of other uses. In this chapter I discuss all of these devices using only pn‐junctions, including solar cells, rectifiers, voltage doublers, surge protectors, and others.

7.1 Solar Cells

One of the most important and valuable applications of the pn‐junction is the solar cell. The solar cell is a very simple application of a diode. It does not need a complicated circuit to understand how it works, just the basic properties of the pn‐junction (see Figure 7.1).

The top figure shows the standard structure of a semiconductor diode, an n‐type material adjoined to a p‐type semiconductor. In the middle we have the depletion or the transition region. This is the region where electrons from the n‐type material diffuse toward the p‐type material and in doing so the n‐type material becomes more positive until the internal potential cancels the diffusion forces. The lower sketch shows the electrostatic potential ...