vbe bipolar
I think is true for Vbe > 0, because the rule Vbe > 0.7V is just an aproximation for fast design .... in Art of Eletronics the autor just says that equation is true if three rules are obeyed:
1) The collector must be more positive then emitter
2) The base emitter and base collector behave like diodes
3) And not exceed Ic, Ib, Vce, Ic*Vce and temperature
they works with this equation.
You can find it on pages 62 and 80.
the correct equation is: Ic = Is*[exp(Vbe/Vt)-1]
leomecma