Hello, A diode is represented by an EMF equal to the electric field in depletion zone plus a resistance. This resistance is obtained from the I/U characteristic of a diode. My question is, this resistance is due to what? The resistivity of P and N junctions or because in forward bias case, there's still a depletion region (electric field) that resists the flow of charges? I know in both case we have an electric field, but in both case is there heat dissipation? Thank you.