A nnpn transistor has an emitter area of 10mm x10mm. The dopingconcentrations are as follows: in the emitterNd=1019 cm3, in the baseNa=1017 cm3, and the collectorNd=1015 cm3. The transistoris operating at T=300K. For electrons diffusing in the base,Ln=17mm and Dn=21.3cm2/s. For holes diffusing in the emitter,Lp=0.6mm and Dp=1.7cm2/s.
Calculate Is and b whenthe base width W is a) 1mm and b)4mm.
c) In the case where W=1um, whathappens to the gain if you decrease the emitter doping toNd=1018 cm3 ?
d) In the case where W=1um, what happens to the gain if you increase the base doping toNa=1018 cm3 with the emitter andcollector doping the same as in part a)?
e) Based on these results, if youwere to design a BJT, what physical and doping characteristics are required to achieve a large gain?