Analysis of Excess Carrier Concentration Control in Fast-Recovery High Power Bipolar Diodes at Low Current Densities

Abstract

The combination of emitter control with local lifetime tailoring by ion irradiation is experimentally analyzed in fast-recovery high power diodes. For this purpose, the carrier lifetime and excess carrier concentration profiles are measured and modeled within the low doped region of unirradiated and helium irradiated diodes under low current densities (<20 A/cm2). The interest in working under these current conditions responds to the fact that the only recombination mechanism that modulates the steady-state carrier concentration is that of the multiphonon-assisted case (Shockley–Read–Hall model). This enables us to extract parameters for their modeling under arbitrary working conditions and to detect the influence of ion irradiation on the excess carrier distribution. For a better comprehension of the results, the excess carrier profile in the unirradiated diode is physically analyzed in detail by an analytical model. Afterward, physical simulations are also carried out, employing the experimental lifetime profiles as input parameters. As a result, a very good agreement between simulation predictions and experiments is observed, which is used to explain, by the support of analytical expressions, how the ion-irradiation process can improve the diode operation at low current densities during the late phase of the reverse recovery.