Work function difference between Gate metal and silicon. This is one source of voltage differences between the Si channel and the gate metal which create band bending in Si. This band bending of, or the voltage drop in, silicon must be first compensated by the applied bias and then an additional bias voltage has to be applied to bend the Si eneergy band enough to induce a charge inversion layer under the gate oxide.

In the following applet, you may change condition in the text field or in the choice box, or mouse drag the Fermi level of silicon.

Best is the gate metal - silicon combination where the work function difference is the smallest.

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