BJT solid state

[brad sue]

Hi i would to a clarification on the base current of BJT.

I would like tto know this:
when is the base current proportional to emitter perimeter and when is it propational to the emitter area?
does the recombination of carriers at the interface has a role in it?

I am reading a difficult book on processing intergation and I was perplex about those statements.

thank you