Electronic – what is the use of a resistor in the PNP transistor

It's a small signal AC model, so the DC currents don't matter. Since \$ \frac{dI_{C}}{dV_{BE}}\$ is the same polarity for both, we can use the same model (i.e. a larger b-e voltage results in a larger load current, just they are both negative for the PNP version (which equates to the same result as the NPN)

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.