The junction diode

A component made of just one p-n junction is a junction diode. It conducts only when forward biased.

Figure to be added

Figure 11.8 — (a) the p and n regions; (b) the diode symbol; (c) the anode (A, +) and cathode (K, −), with current flowing in the direction of the arrowhead.

Anode and cathode

The + terminal is the anode (A) and the − terminal the cathode (K). The diode conducts only when the anode is made positive, and the arrowhead of its symbol shows the direction of the current.

Figure to be added

Figure 11.9 — a junction diode: a black cylinder with a white or silver band at the cathode end.

Diodes are marked with a number to tell them apart. Not every diode looks like this one.