Tunnel Diode

Solid State Devices and Solid State Power Supplies and Amplifiers
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TC 9-62

TUNNEL DIODE - a heavily doped PN junction that exhibits negative resistance

over part of its range of operation. The heavy doping causes the tunnel diode

to have a very narrow depletion region and also causes the valence band of one

of the semiconductor materials to overlap the energy level of the conduction

band of the other semiconductor material. At the energy overlap point,

electrons can cross from the valence band of one material to the conduction

band of the other material without acquiring any additional energy. This action

is called tunneling. Tunnel diodes are used as amplifiers, oscillators, and high-

speed switching devices.

VARACTOR - a diode that exhibits the characteristics of a variable capacitor. The

depletion region at the PN junction acts as the dielectric of a capacitor and is

caused to expand and contract by the voltage applied to the diode. This action

increases and decreases the capacitance. Varactors are used in tuning circuits

and can be used as high-frequency amplifiers.

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TC 9-62

23 June 2005

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