Transient Response Characteristics of Unijunction Transistors

Carrier transport in unijunction transistors is due primarily to electric fields rather than diffusion gradients. Thus, the high-frequency and transient response characteristics of unijunction transistors are considerably different from the characteristics associated with diffusion type devices. The high-frequency and transient response characteristics of silicon unijunction transistors are described. A previously published solution of the electrodynamic equations, taking into account field and recombination effects, is used to calculate theoretical frequency and transient response characteristics which are subsequently compared to experimental measurements. It is shown that: 1) Electric field effects lead to resonance characteristics which are somewhat similar to those encountered in wave interference phenomena. 2) The frequency response characteristics of unijunction transistors are predominantly determined by the electric field gradient for high fields and by recombination effects for low fields. 3) The large-signal transient response of unijunction transistors is characterized by at least two time constants, one of which is related to transit time and the other to minority carrier lifetime. 4) The maximum large-signal switching speeds and minimum trigger energy of regenerative unijunction transistor circuits depend upon both the electric field and lifetime characteristics of the device.