Junction under DC forward bias

Under a DC forward bias (V>0) and within the framework of the weak injection model, the total current flowing through the diode is an exponential function of the applied bias V. However, if the forward bias is very high, the ohmic resistances of the two N- and P-doped parts are not negligible any more. It is no longer possible to assume that the voltage applied to the device (noted Va) does not induce a voltage drop in these doped regions; instead it must be written as where V is the voltage required to lower the junction potential barrier to a value around kT/q while represents the voltage drop due to the ohmic resistance of the N and P regions.