PREBREAKDOWN AND BREAKDOWN PHENOMENA IN HIGH-FIELD SEMICONDUCTOR-DIELECTRIC SYSTEMS

The complexity of the semiconductor-dielectric system behavior under h igh electric fields is discussed. Time dependence of the voltage drop, electrical current, and light emissions, and the strong influence of the nature and quality of the surrounding dielectric, as well as the q uality of the semiconductor processing and contacts, are analyzed for high-purity bulk silicon-dielectric vacuum or gas systems under impuls e voltage stress. On the basis of the analysis of the main characteris tics of the time response of the system up to breakdown, as well as of the variation of the current components with the applied voltage, a n ew comprehensive physical model of the prebreakdown and breakdown phen omena in the high-field semiconductor-dielectric systems is proposed. The model points out the active behavior of two parts, the semiconduct or and the ambient dielectric, and the main role of the semiconductor in the initiation of the breakdown phenomena in the system. Based on a large number of experimental results, the present model proposes two totally different breakdown processes in semiconductor-dielectric syst ems: surface flashover and semiconductor bulk breakdown, depending on the defect distribution in the semiconductor. The key to the model is offered by the role of the conduction currents in the semiconductor, e specially by the local avalanche current generated by avalanche proces ses in defect zones of the crystal, for fields much smaller than the t heoretical intrinsic breakdown field of the material. The main charact eristics of the prebreakdown and breakdown response of the system for different conditions are explained on the basis of the proposed model. A short discussion of the main reported results of other groups is al so presented in view of the new physical model. The role of the semico nductor and ambient-dielectric quality, as well as of the system confi guration quality in the breakdown phenomena of high-field semiconducto r-dielectric systems, are emphasized on the basis of the proposed mode l.