page_title: Gunn diode
section_title: Applications
hierarchical_section_title: Gunn diode / Applications
caption_attribution_description: English: Inside a disassembled radar speed gun, used by police to measure the speed of cars. The copper-colored cone is the horn antenna which emits the beam of microwaves. The small grey unit mounted at its apex is a 24GHz Gunn diode oscillator which generates the microwaves. The GaAs Gunn diode is mounted inside a resonant waveguide cavity diecast from Mazak zinc aluminium alloy.
context_page_description: A Gunn diode, also known as a transferred electron device, is a form of diode, a two-terminal semiconductor electronic component, with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 1962 by physicist J. B. Gunn. Its largest use is in electronic oscillators to generate microwaves, in applications such as radar speed guns, microwave relay data link transmitters, and automatic door openers.
  Its internal construction is unlike other diodes in that it consists only of N-doped semiconductor material, whereas most diodes consist of both P and N-doped regions. It therefore does not conduct in only one direction and cannot rectify alternating current like other diodes, which is why some sources do not use the term diode but prefer TED. In the Gunn diode, three regions exist: two of those are heavily N-doped on each terminal, with a thin layer of lightly n-doped material between. When a voltage is applied to the device, the electrical gradient will be largest across the thin middle layer.
context_section_description: Because of their high frequency capability, Gunn diodes are mainly used at microwave frequencies and above.  They can produce some of the highest output power of any semiconductor devices at these frequencies.   Their most common use is in oscillators, but  they are also used in microwave amplifiers to amplify signals.  Because the diode is a one-port (two terminal) device, an amplifier circuit must separate the outgoing amplified signal from the incoming input signal to prevent coupling.  One common circuit is a reflection amplifier which uses a circulator to separate the signals.    A bias tee is needed to isolate the bias current from the high frequency oscillations.
caption: Disassembled radar speed gun.  The grey assembly attached to the end of the copper-colored horn antenna is the Gunn diode oscillator which generates the microwaves.
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