1) why the energy band bends near the insulator semi conductor interface?
2)why the fermi level at the metal portion goes upward or backward due to the application of gate potential?
3)instead of using the insulator between the semi conductor and metal gate if we directly insert the gate to the channel region then what will happen? is there any advantage using the insulator?
4)for doping by the donar type impurity to a samy conductor the fermi level moves upward and come closer to conduction band. why?
Sorry, your question is outside of my experience as it relates more to molecular energy theory than electronics. However, I think the following may be of use for your further understanding.
Best wishes to you. It was a good question, sorry I could not give you a more precise answer.