The Impact Avalanche Transit Time (IMPATT) diode is a high power radio frequency (RF) generator that operates from 3 to 100 GHz. IMPATT diodes are manufactured from silicon, gallium arsenide or silicon carbide.
An IMPATT diode is reverse biased above the breakdown voltage. The high doping levels produce a thin depletion region.
![Principle of IMPATT diode Principle of IMPATT diode](https://i0.wp.com/www.electricalandcontrol.com/wp-content/uploads/2023/09/Principle-of-IMPATT-Diode.png?resize=247%2C196&ssl=1)
The arising high electric field rapidly accelerates carriers which free other carriers in collisions with the crystal lattice. Holes are swept into the P+ region. Electrons drift toward the N regions. The cascading effect creates an avalanche current which increases even as voltage across the junction decreases. The pulses of current lag the voltage peak across the junction. A “negative resistance” effect in conjunction with a resonant circuit produces oscillations at high power levels.
![Oscillator circuit with an IMPATT diode in use Oscillator circuit with an IMPATT diode in use](https://i0.wp.com/www.electricalandcontrol.com/wp-content/uploads/2023/09/IMPATT-diode-in-use-.png?resize=264%2C159&ssl=1)
The DC reverse bias is applied through a choke which keeps RF from being lost in the bias supply. Low power RADAR transmitters may employ an IMPATT diode as a power source.
Related: The Shockley Diode Features & Operation