How
does the gate bias in a Tunnel Field Effect Transistor align the
conduction band of the intrinsic region with the valence band of the P
region?
I understand that once aligned, the electrons can tunnel through the
boundary, but I don't understand how the applied voltage at the gate
"aligns" the two bands.
An appropriate gate voltage will raise the energy of the valence band
electrons to an energy equal (or maybe just close to) the conduction
band. At this point the semiconductor changes from insulator to
conductor.
Voltage is a measure of the potential energy of electrons, IRCC.
Raise the voltage and your raise the PE of electrons in the vicinity.
In this case, the potential energy of the intrinsic conduction band is
lowered by increasing voltage, until it is down to the level of the
p-type valence band, allowing for tunneling.
One volt is defined as "the potential difference over which a positive
coulomb of charge gains one Joule of potential energy".
So the
direction of voltage is tied to the arbitrary definition of charge, in
order to make it match up with the non-arbitrary definition of energy.
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