The Diode

When wafers of n-type and p-type material are in physical contact, the result is a p-n junction with certain properties. Figure 1 shows the electronic symbol for a semiconductor diode. The n-type material is represented by the short, straight line in the symbol and is the cathode. The p-type material is represented by the arrow and is the anode.
In a perfect diode, electrons flow in the direction opposite the arrow but cannot flow in the direction the arrow points. If a battery and resistor are connected in series with a diode, current flows if the cathode is negative relative to the anode (Fig. 2a) but does not flow if the battery is reversed (see Fig. 2b). This is an example of something with which you should by now be familiar: the idealized scenario! In the real world, diodes can approach but never attain this state of perfect one-way conduction.

Fig.1. Anode and cathode symbology for a diode.

Fig. 2. (a) Forward bias of a diode results in a flow of current. (b) Reverse
bias normally produces near-zero current.