Impatt Diodes:

The acronym IMPATT (pronounced as "IM-pat") comes from the terms impact avalanche transit time. We won't anxiety ourselves in this section with the precise nature of this effect, except to note that it is similar to negative resistance. The IMPATT diode is a microwave oscillating device such as a Gunn diode, though it is produced with silicon instead of gallium arsenide.

An IMPATT diode can be used as a low-power amplifier for the microwave radio signals. As an oscillator (a circuit which generates rf ac), an IMPATT diode generates around the same quantity of output power, at analogous frequencies, as a Gunn diode.