Avalanche-and-Transit Time Diode

a semiconductor device with negative resistance that arises because of a phase shift between the current and the voltage at the terminals of the device as a result of the inertial properties of the avalanche multiplication of charge carriers and the finite time of their transit in the region of the p-n junction. The avalanche multiplication in the p-n junction is caused by collision ionization of atoms by the charge carriers. In contrast to other devices in this class (tunnel diodes, thyristors, and Gunn diodes), the negative resistance of avalanche-and-transit time diodes appears only at superhigh frequencies. The idea of creating this type of diode was first formulated by the American physicist W. Read in 1958. The generation of oscillations using an avalanche-and-transit time diode was first observed experimentally in the USSR by a group of researchers directed by A. S. Tager.

Avalanche-and-transit time diodes are used to generate oscillations in the frequency range from 1 to 300 gigahertz. The power of the oscillations is several watts, with an efficiency of the order of 10 percent. In 1967 a new mode of operation of the diode was discovered, in which electric oscillations arise simultaneously at two frequencies: the frequency f₀, which is characteristic of the conventional mode of operation, and its subharmonic f₀/n, where n Ⓗ 3. This mode is distinguished by its high efficiency (up to 60 percent) and by the high level of output power at subfrequencies (up to several hundred watts).

Avalanche-and-transit time diodes can be made from structures of the p⁺-n-i-n⁺ type (the Read diode) or the p-i-n, p-n, p⁺-n, and p-n⁺ types, formed by impurity diffusion, by ion implantation, by epitaxy, or by vacuum deposition, with formation of a Schottky barrier. The semiconductor materials used in the fabrication of such diodes have a high drift rate of the charge carriers, as well as a wide forbidden gap (GaAs, Si, and Ge).