Unequal space charge region widths and deviation of avalanche region centre in symmetrical pulsed double-drift IMPATT diode

Unequal space charge region widths on the p and n sides of a symmetrical double drift Si IMPATT diode are observed under pulsed operating conditions. The space charge region width on the p side is greater than its value on the n side and the difference is appreciable at higher current densities. This unusual behaviour in a symmetrical structure is attributed to the carrier´s space-charge effect. Moreover, the deviation of the avalanche region centre from the p-n junction interface is not significant at mm-wave frequencies, as commonly believed. The inequality in space charge region widths in symmetrical structure starts in the range of current levels where the conventional design mode is valid. It thus violates conventional design criteria and reduces the diode´s Q and efficiency. An optimisation method for improved performance of pulsed IMPATT diodes in the conventional design mode is presented and shown by extending Chang and Ebert´s (1980) symmetrical optimum design for 10-15 W pulsed power at 94 GHz