OPtimum Low-Level Injection Efficiency of Silicon Transistors with Shallow Arsenic Emitters
The influence of As surface concentration CsE on the emitter efficiency βϒ and the temperature dependence of βϒ are reported. The theoretical model that is used to explain the variation ofβϒ with CSE is based upon the difference in the effective energy bandgaps in the emitter and base regions ΔEg. Experimental measurements of ΔEg versus CSE are presented. Measurements of β, versus CSE show that the effective emitter doping density QE/X5 reaches a maximum value at CSE≌1.5 × 1020 atoms /cm3, corresponding to the threshold above which ΔEg>0. For the case of a constan: active base doping/em2 QB, this also corresponds to an optimum ir. the emitter efficiency βϒ. However, it is shown that in typical sequential diffusion processing of transistors, βϒ increases monotonically with CBE because QB =QB(CSE) decreases. In addition, for devices fabricated in this study, Δβ/ ΔCSE at CSE = 2 × 1020 atoms/ cm3 for As-diffused emitters (doped oxide) was≈ 5 times greater than for ion-implanted-diffused As emitters, showing the superiority of implantation in controlling gain. Finally, transistors that were made with [ommited formula]. © 1973, IEEE. All rights reserved.
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