Diffusion current and resistance of a diode In a diode, there is a resistance  in the p and n region, and electric field is required to move the charges in forward bias conditions. My question is: when there is diffusion current is the electric field helping the diffusion current because of the resistance? Thus can we say this is also a drift current?
 A: There seems to be some confusion about carrier motion on your part. Carrier diffusion occurs all the time - in a field-free region the net will eventually go to zero in steady state (but carriers are still moving and diffusing around). Drift current is the result of the (slight)  bias in charge carrier motion caused by an applied electric field. No field, no drift current, just diffusion. With field, both drift and diffusion, but the drift is the portion caused by the presence of the field. Resistance is caused by carrier scattering processes, and impacts both drift and diffusion equally.
The separation of current into drift and diffusion is physicists imposing a model for carrier motion where we want separate it into those two terms. It isn't like you can paint some electrons red, and say they are only drifting, while those blue ones over there are only diffusing - it is all the same electrons executing a complicated motion that is a combination of random diffusion (field or no field) and drift under the applied field.
Resistance is then the scattering (and resulting momentum scrambling) of the electrons. The more times they scatter and forget where they are going, the harder it is to make them eventually go in the direction the field is pointing.  
