Physical modeling of avalanche-transistor switching

The phenomenon of avalanche second breakdown in epitaxial planar transistors was studied. It is shown that there are two distinct modes of avalanche second breakdown operation: (1) due to temperature rise the thermal mode; and (2) due to excess injection of current under high voltage bias, the current mode. For a fast switching avalanche transistor, the current mode second breakdown is dominant. A two dimensional analysis is used to model the final destruction of the device. When the duration of the second breakdown in an avalanche transistor is limited however such a device is used as a rather fast and repeatable electrical switch, such as in a pulse generation circuit. To design an avalanche transistor for particular applications or to choose an avalanche transistor for a specific circuit, the fundamental relations between the basic structure of the device and its quasisteady-state operational characteristics, together with its operational limitations, are important. It is suggested that the second breakdown is a result of an expanding plasma wave.