User:John R. Brews/Draft

A semiconductor diode is a two-terminal device that conducts current in only one direction, made by joining a p-type semiconducting layer to an n-type semiconducting layer.

Electrical behavior

(PD) Image: John R. Brews
Nonideal pn-diode current-voltage characteristics.

The ideal diode has zero resistance for the forward bias polarity, and infinite resistance (conducts zero current) for the reverse voltage polarity. The pn-diode is not ideal. As shown in the figure, the diode does not conduct appreciably until a nonzero knee voltage (also called the turn-on voltage) is reached. Above this voltage the slope of the current-voltage curve is not infinite, but exhibits a nonzero forward resistance. In the reverse direction the diode conducts a nonzero leakage current (exaggerated by a smaller scale in the figure) and at a sufficiently large reverse voltage below the breakdown voltage the current increases very rapidly with more negative reverse voltages.

Types

Semiconductor diodes come in a large variety of types:

• pn-diode: The pn junction diode consists of an n-type semiconductor joined to a p-type semiconductor.
• Zener diode: The Zener diode is a special type of pn-diode made to operate in the reverse breakdown region. The breakdown voltage in these didoes is sometimes called the Zener voltage. The diode is not destroyed in this mode of operation because it is made up of very heavily doped semiconductors leading to Zener breakdown, an electron tunneling behavior, rather than a destructive avalanche breakdown.
• Schottky diode: The Schottky diode is made using a metal such as aluminum or platinum, on a lightly doped semiconductor substrate.
• Metal-oxide varistor: The varistor works like a Zener diode in both voltage directions.
• Tunnel diode: Like the Zener diode, the tunnel diode is made up of heavily doped n- and p-type layers. Conduction takes place by electron tunneling.
• Light-emitting diodes: The light-emitting diode is designed to convert electrical current into light.