Forward transient charge injection in psn diodes at medium to high injection levels

The forward transient in psn power diodes has been studied. A new expression, simpler than the conventional one, has been developed for the evolution of the carrier distributions in response to a current step in pin diodes. The usefulness of this expression as an approximate solution for lightly doped psn rectifiers is considered. A critical current density is derived, above which a psn diode behaves as a pin diode. This critical current density is shown to be useful for designing drift step-recovery diodes, and other similar modern power structures that require pulsed forward biasing. In particular, it allows the bias current to be chosen so as to minimize the step-recovery ramp voltage, and it allows an estimate of the maximum stored charge in a drift step-recovery diode commensurate with step-recovery action.