I am working on Gate All Around Nanowire MOSFET, if the semiconductor is n-type, therefore threshold voltage should be negative value. so how the workfunction difference between metal and semiconductor shifts the threshold voltage to positive values?
I think depletion mode devices are slow in speed of operation as compared to enhancement mode devices and hence depletion mode is normally used as pull up load with source connected to gate.
as far as my knowledge goes modifying work function might not help in this particular case.
Two suggestion from my side.
Better Follow aparna,
Otherwise If you dont want to change material controlled it using other supply which I think not a viable solution
Dear Ahmed,
In order to make the transistor with n-type substrate normally off you have to deplete it through the contact difference of potential between the gate material and the substrate material. That is the work function of the gate material must be much blow the fermi level of the n-substrate material such that depletion layer forms at the surface of the n- semiconductor. It is said that the gate metal builds Schottky diode with the substrate. If one makes the thickness of the n-substrate smaller than the equilibrium space charge layer width, then full depletion occurs. Therefore the transistor will be normally off. To make it conducting, one has to apply positive voltage on the gate to reform the channel
and make the transistor conducting.
Best wishes
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