Understanding Image Force: Barrier or Reducer?

[ssegga]

i don't quite understand how it operates.
from what i read it seems the image force is part of the barrier.
but the textbook says it reduces the barrier.
which is which?

 

[marlon]

The Schottky effect expresses the change in electrostatics at a metal /semiconductor(=SC) -interface. This change arises because charges will flow from one side to the other. For example electrons will flow from an n-type SC to the metal.

Once part of the SC conduction electrons have traveled to the metal, the positive donor-atoms remain unscreended. They give rise to a region which is positively charged (ie the depletion region) of a few nanometers thick (measured from the interface). Because of Poisson's Law, the energy bands will be bent due to this positive space charge.

This positive space charge at the SC side of the interface will yield a negative image charge at the metal side of the interface. The positive region at the SC-side "attracts" electrons from the metal-side. These electrons will not flow back toward the SC because they do not have enough energy to do so. We only get a local region of higher electron density at the metal side. This is the image charge and its effect is to lower the Schottky barrier height (SBH). This SBH is defined as the energy difference between the metal fermi level and the bottom of the n-type SC conduction band.

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marlon