D. C. Current amplification factor of junction transistors

In the design of transistors for class B amplifier and switching applications, a primarily important parameter is the D. C. current amplification factor. By extending the work of Shockley, Webster and Rittner, a theoretical expression has been derived for the variation of this D.C. current amplification factor versus emitter current at high injection levels. Calculations have been made based upon this theoretical expression. Results are presented for emitter currents up to the amperes range with different values of resistivity, life time, width and surface recombination velocity of the base region, and different values of conductivity and diffusion length of the emitter region as well as the size of the emitter-base junction. These results provide a quantitative guide for the design of power transistors. Recent reports, indicate that by using new alloys for p-n-p fused junction transistors, the current amplification factor can be improved tremendously. One of the speculations is that this improvement is caused by the increase in emitter conductivity. Theoretical and experimental results are given to review this speculation quantitatively.