p-n-p-n charge dynamics

A simple unified charge model applicable to both unsaturated and saturated p-n-p-n dynamic behavior is analyzed. Expressions are obtained for three important dynamic conditions: di/dt prior to saturation, voltage drop during turn-on, and reverse current during recovery. Comparison with measurement shows that interdigitated gate p-n-p-n devices match one-dimensional turn-on theory and closely approximate the behavior of p-i-n rectifiers under similar pulsed conditiom. The major analytical simplifications of the one-dimensional theory are examined in the Appendixes. The limitations imposed by these simplifications can be avoided by use of numerical integration techniques.