On the variation of small-signal alphas of a p-n-p-n device with current

Abstract

The physical mechanisms that govern the variation of alphas of a silicon p-n-p-n device with current are investigated and an analytical expression for the small-signal alphas is derived. It is shown that both diffusion and electric field contribute to the transport of carriers and, therefore, affect the device transport factors and injection efficiencies. The value of alpha can be tailored to the desired range by choosing properly the base width, the diffusion length and the doping levels. A numerical example is worked out and the small-signal alpha, the d.c. alpha, the transport factor and the injection efficiency are plotted as functions of current for several values of base width of the p-n-p section of a p-n-p-n device. It is seen that the small-signal alpha is always greater than the d.c. alpha in the current range investigated. © 1967.