Semiconductor Diodes and the Unijunction Transistor

Abstract

A diode is a two-terminal device, one terminal being known as the anode and the other as the cathode (see figure 3.1a). The characteristic curve of an ‘ideal’ diode is shown in figure 3.1b. The characteristic of the diode shows that when the anode is positive with respect to the cathode, it functions as though it were a switch whose contacts are closed; in this state the p.d. across the ideal diode is zero for all values of current, and the diode is said either to be in its forward biased mode or in its forward conducting mode. When the anode is negative with respect to the cathode, the diode functions as though it were a switch whose contacts are open; in this state no current flows through the diode for all values of voltage, and it is said either to be in its reverse biased mode or in its reverse blocking mode.