there is such an equation pn = ni^2 exp(Va/Vt) in junction given in textbook. I am wondering how true it is against other equations. suppose Va is zero, pn = ni^2 exp(Va/Vt) => pn = ni^2 at same time p is p(0)= Ni^2/Nd, and n(0) = Ni^2/Na, so...