Thanks

You may read paper entitled "Nanowire transistors without junctions"  to understand the physics of the junctionless transistors. Please, follow the link.

http://www.nature.com/nnano/journal/v5/n3/full/nnano.2010.15.html

Thanks, but junctionless transistor is normally on devices which conduct current at zero gate voltage, but in the paper entitled"Nanowire transistors without junctions" it appears that for n-type transistor it does not conduct current at zero gate voltage. so, as the describes that the workfunction difference between metal and semiconductor is the reason for shifting the threshold voltage to positive values

Thank you very much for your answer