Editing Gunn diode (section)

==Gunn diode oscillators==
[[Image:Gunn diode IV curve.svg|thumb|Current–voltage (''I''–''V'') curve of a Gunn diode. It shows [[negative resistance]] above the threshold voltage (''V''<sub>threshold</sub>).]]

The negative differential resistance, combined with the timing properties of the intermediate layer, is responsible for the diode's largest use: in [[electronic oscillator]]s at [[microwave]] frequencies and above. A microwave oscillator can be created simply by applying a [[Direct current|DC]] voltage to bias the device into its negative resistance region. In effect, the diode's negative differential resistance cancels the load circuit's positive resistance, thus creating a circuit with zero differential resistance, which will produce spontaneous oscillations. The oscillation [[frequency]] is determined partly by the properties of the middle diode layer but can be tuned by external factors. In practical oscillators, an electronic [[resonator]] is usually added to control frequency in the form of a [[waveguide]], [[microwave cavity]], or [[YIG sphere]]. The diode is usually mounted inside the cavity. The diode cancels the resonator's loss resistance, producing oscillations at its [[resonant frequency]]. The frequency can be tuned mechanically, by adjusting the size of the cavity, or in the case of YIG spheres, by changing the [[magnetic field]]. Gunn diodes are used to build oscillators in the 10 [[GHz]] to [[Terahertz radiation|THz]] frequency range.

[[Gallium arsenide]] Gunn diodes are made for frequencies up to 200&nbsp;GHz, [[gallium nitride]] materials can reach up to 3 [[Terahertz (unit)|terahertz]].<ref>V. Gružinskis, J. H. Zhao, O. Shiktorov and E. Starikov, [http://www.scientific.net/MSF.297-298.341 "Gunn Effect and the THz Frequency Power Generation in n<sup>+</sup>–n–n<sup>+</sup> GaN Structures"], Materials Science Forum, 297–298, 34–344, 1999.</ref><ref>Gribnikov, Z. S., Bashirov, R. R., Mitin, V. V. (2001). "Negative effective mass mechanism of negative differential drift velocity and terahertz generation". IEEE Journal of Selected Topics in Quantum Electronics, 7(4), 630–640, {{doi|10.1109/2944.974235}}.</ref>