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 and high field) in which avalanche