A student is trying to create a homebrew pnp BJT by connecting together the cathode terminals of two separate pn diodes to obtain the n-type base, and by designating one of the anodes as the p-type...

A student is trying to create a homebrew pnp BJT by connecting together the cathode terminals of two separate pn diodes to obtain the n-type base, and by designating one of the anodes as the p-type emitter, and the other as the p-type collector. Soon, the student fi nds that the resulting device doesn’t provide any base-current amplifi cation. Why? List at least two reasons. (b) Undaunted, the student decides to use the B-E junction of one pnp BJT sample and the B-C junction of another pnp BJT sample to meet the relative doping constraints needed of a BJT. He then connects together their base terminals to form the base terminal of the composite device. The student still fi nds that the device doesn’t provide any current gain. Why?