UNEQUAL SPACE-CHARGE REGION WIDTHS AND DEVIATION OF AVALANCHE REGION CENTER IN SYMMETRICAL PULSED DOUBLE-DRIFT IMPATT DIODE

Unequal space charge region widths on the p and n sides of a symmetric al double drift Si IMPATT diode are observed under pulsed operating co nditions. 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 cu rrent densities. This unusual behaviour in a symmetrical structure is attributed to the carrier's space-charge effect. Moreover, the deviati on of the avalanche region centre from the p-n junction interface is n ot significant at mm-wave frequencies, as commonly believed. The inequ ality in space charge region widths in symmetrical structure starts in the range of current levels where the conventional design mode is val id. It thus violates conventional design criteria and reduces the diod e's Q and efficiency. An optimisation method for improved performance of pulsed IMPATT diodes in the conventional design mode is presented a nd shown by extending Chang and Ebert's symmetrical optimum design for 10-15W pulsed power at 94GHz.