The Role of Carrier Lifetime in Forward Bias Degradation of 4H-SiC PiN Diodes

摘要

The role of excess carrier lifetime reduction in the mechanism for on-state voltage (V_f) degradation of high voltage 4H-SiC PiN diodes is investigated. A method is developed to electrically monitor the emitter, base, and end region excess carrier lifetimes at periodic intervals during the forward bias stress condition. The lifetime measurement method involves using the turn-off reverse-recovery waveforms for conditions of high dI/dt and low dV/dt. The peak reverse-recovery current for high dI/dt is related to the excess carrier charge stored before the diode is switched off and is an indication of the total recombination rate. The low dV/dt condition minimizes the carrier sweep out and diffusion currents resulting in a current tail with a decay rate that is determined by the base and end-region lifetimes. This lifetime measurement method is used to monitor diodes with degradation times ranging from one minute to over several hundred hours. The measurements indicate that V_f degradation is accompanied by a reduction in end region lifetime and/or reduction in device conduction area.