Theory of Alpha for P-N-P Diffused Junction Transistors

Equations are developed for the emitter and collector currents for this type of transistor, and the resulting expressions are then used to obtain the current-gain factor. The low-frequency value of the current-gain factor and its high-frequency cutoff value are shown to depend strongly on the width of the base region, the behavior at high frequencies being better for small base width. The high-frequency behavior when used in grounded emitter applications depends more directly on the lifetime of holes in the germanium and shows only a second-order dependence on the base width; the lower the lifetime the higher the frequency cutoff value.