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.
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.
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.
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