Apply the gummel poon model to estimate Ic, Ie and Ib for a pnp transistor to be used in next generations of iPhones if Is= 10^-16 A, br=0.40, Veb=0.75v and Vcb=+0.70v

For what purpose is a PNP junction transistor is used? Explain in detail how it is used. 
b) If you have pure Si, P, Ge, As, Ga, and Al materials which ones would you choose to create a PNP junction transistor and why?

What is an NPN transistor?