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Re: Why n plus is used instead of n minus for diffusion regi
as you know that in case of nmos,substrate is p-type so for the formation of channel depends on +ve gate voltage and since the substrate is p-type it has holes as the majority carriers and electrons as minority
so, when the small +ve voltage is applied at the gate the -ve charge will start coming closser to form a channel but it will not be enough for the current to flow across drain and source.
as gate is made more +ve more -ve charges come closser between the source and drain and these excess electrons are provided by n+ regions
so it has to be n+ to provide these excess electrons for the formation of invertion layer and the current to flow.