3.1 P-N JUNCTION

All modern semiconductor devices and integrated circuits (IC), which are the backbone of modern day electronics, contain at least one junction between p-type and n-type semiconductor, commonly known as p-n junction. This p-n junction is the most fundamental semiconductor device as all other devices like various types of transistors (Bipolar Junction Transistor, Field Effect Transistor, Metal Oxide Semiconductor Field Effect Transistor, etc.) require p-n junctions of various configurations, which will be discussed in subsequent chapters. Various analog and digital operations and performance like rectification, amplification, switching, logic operations require this fundamental semiconductor device. In this chapter, we will discuss various issues related to the p-n junction followed by application of such junction diodes, called p-n junction diodes, for various operations.

In chapter 2, we have been familiar with different types of semiconductors, classified in different aspects. We recall p- and n-type semiconductor, which are realized by doping an intrinsic semiconductor with different type of impurities to obtain large number of free carriers in the form of holes in p-type semiconductor and electrons in n-type semiconductor, respectively. However, these n-type and p-type semiconductors having electrons and holes in abundance are electrically neutral, as they are neutralized by the impurity ions which have created them. To be more specific, electrons are neutralized by associated donor ions, each of which has equal (opposite in sign) amount of charge as that of each electron, and holes are neutralized by acceptors ions, each of which has equal (opposite in sign) amount of charge as that of a hole, ensuring a charge neutrality. This is clearly shown in Figure 3.1. However, if we consider a semiconductor whose two sides are differently doped with acceptor and donor impurities, their effect is not like two isolated pieces of p- and n- type semiconductor due to the transport phenomena of the mobile charge carriers. Such a device is known as p-n junction and needs to be discussed in detail. It is the most fundamental semiconductor device and is the backbone of modern day electronics.