Small-signal characteristics of semiconductor punch-through injection and transit-time diodes

Abstract

The two terminal impedance characteristics of the semiconductor punch-through structure are examined for operation under low-field, i.e. constant mobility, conditions. It is shown that a straightforward analytical description can be obtained by the use of the complex number methods of alternating current theory. Various modes of operation are described as characterised by space-charge-limited injection, emission-limited injection and barrier-limited injection. Negative resistance is found in all cases and is due to the propagation of space-charge waves which move in anti-phase with the local field through a substantial volume of the device. The negative resistance effects are increased by the use of low-mobility material which increases the phase lag of current. Series resistance and series capacitance are calculated as functions of frequency and current bias for representative silicon devices. The magnitude of the available negative resistance is numerically small in the low-field structure and is unlikely to lead to practical applications. However, the analysis which is presented provides insight into the working mechanisms of the high-field structure and this device, known as the punch-through transit-time diode or BARITT diode, is already proving to have practical value in microwave systems.