On the Transient Behavior of Semiconductor Rectifiers

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Abstract
If the forward current through a p‐n junction suddenly ceases, an emf appears due to nonequilibrium carrier concentrations at the junction barrier. Measurements of the barrier emf have been made with a wide range of injection currents and yield current vs barrier voltage characteristic curves. The open circuit case of voltage decay across a p‐n junction in the range V≫kT/q is discussed. The voltage decay is observed to be linear with time with a slope kT/qτ. It follows from an analysis based on a simple model that the excess minority carrier concentrations decrease exponentially with the time constant τ. The floating emitter and collector voltages, VE(t) and VC(t), of p‐n‐p transistors are observed to decay like the open circuit voltage across a p‐n junction, and it is noted that VE(t) ≈ VC(t) in the range V≫kT/q. The transient response of a semiconductor rectifier connected in parallel with a large external capacitance is analyzed. The response calculated for large negative excursions of voltage gives a simple relation by which the saturation current may be determined. Measurements are presented and discussed.