Doped PNP Bipolar Transistor

Question

When doping a PNP bipolar transistor, does it matter which parts are doped by what amount? The picture below will show my question. Am I right in saying that the Emitter is connected to one P region, the Base is connected to the N region and the collector is connected to another P region?

The confusing part in the question is that it says "not in that order". So can I just use the values given to dope the regions in any random way. Or does the Emitter area require the highest doping amount or the base area the lowest amount etc.

Thanks

Answer 1

Any Bipolar junction transistor (BJT) constitutes :

1. a heavily doped emitter
2. a lightly doped and small size base
3. a moderately doped collector

So according to your question, the emitter should have been doped to a concentration of 10^23/cm^3, the base doped to 10^16/cm^3 and the collector doped to a concentration of 10^18/cm^3.

Now your assumption about the emitter being connected to a P region, the base to a N region and the collector to a P region is correct.

And keep in mind that a Si atom has 4 valence electrons and that hole concentration will be in the order: emitter > collector > base and reverse for electron concentration.The calculations are quite easy to do.