Avalanche Breakdown in Silicon

An avalanche theory of breakdown at room temperature is proposed for semiconductors based on the assumption of approximately equal ionization rates for electrons and positive holes. The problem of obtaining ionization rates from data obtained in inhomogeneous fields is solved exactly for two specific field distributions. Ionization rates for silicon thus calculated from experimental data on breakdown voltage and on prebreakdown multiplication for both linear-gradient and step junctions are in good agreement. The temperature coefficient of the ionization rate exhibits a similar internal consistency. It is concluded that internal field emission has not been observed in silicon.Detailed observations are reported of the pulse-type noise associated with breakdown. It is shown that this noise represents the unstable onset of breakdown and that, for the junctions studied, all of the current flow in the breakdown region can be attributed to the current carried by the noise pulses.