Editing IMPATT diode (section)

==Device structure==
The IMPATT diode family includes many different [[Electrical junction|junctions]] and metal [[semiconductor device]]s. The first IMPATT oscillation was obtained from a simple silicon [[p–n junction]] diode biased into a reverse avalanche break down and mounted in a microwave cavity.  Because of the strong dependence of the ionization coefficient on the electric field, most of the electron–hole pairs are generated in the high field region. The generated electron immediately moves into the N region, while the generated holes drift across the P region. The time required for the hole to reach the contact constitutes the transit time delay.

The original proposal for a microwave device of the IMPATT type was made by Read. The Read diode consists of two regions (1) the avalanche region (a region with relatively high [[doping (semiconductor)|doping]] and high field) in which avalanche multiplication occurs and (2) the drift region (a region with essentially intrinsic doping and constant field) in which the generated holes drift towards the contact. A similar device can be built with the configuration in which electrons generated from the avalanche multiplication drift through the intrinsic region.

An IMPATT diode generally is mounted in a microwave package. The diode is mounted with its low–field region close to a silicon [[heat sink]] so that the heat generated at the diode junction can be readily dissipated. Similar microwave packages are used to house other microwave devices.

The IMPATT diode operates over a narrow frequency band, and diode internal dimensions must correlate with the desired operating frequency. An IMPATT oscillator can be tuned by adjusting the resonant frequency of the coupled circuit, and also by varying the current in the diode; this can be used for [[frequency modulation]].