10.11:
Fermi Level Dynamics
The vacuum level represents the energy threshold for an electron to escape a material's surface. It typically lies above a semiconductor's conduction band and serves as a reference for electron energies.
In semiconductors, electron affinity is the energy gap between the conduction band minimum and the vacuum level.
The work function is the minimum energy required to liberate an electron from the Fermi level to the vacuum level and is material-dependent.
Metals exhibit high work functions, around 2 to 5 eV, due to their dense Fermi level states.
Semiconductors exhibit variable work functions as their Fermi levels change, influenced by doping and temperature.
A metal and semiconductor in contact achieve equilibrium, creating a continuous vacuum level across the junction.
Simultaneously, charge transfer continues until the Fermi levels align, causing energy band bending in the semiconductor and forming a Schottky barrier.
The junction's barrier height is determined by the metal's work function and the semiconductor's electron affinity.
10.11:
Fermi Level Dynamics
The vacuum level denotes the energy threshold required for an electron to escape from a material surface. It is usually positioned above the conduction band of a semiconductor and acts as a benchmark for comparing electron energies within various materials.
Electron affinity in semiconductors refers to the energy gap between the minimum of its conduction band and the vacuum level and it is a critical parameter in determining how easily a semiconductor can accept additional electrons.
The work function represents the least amount of energy required to move an electron from the Fermi level, which is the energy level where an electron has a 50% chance of being present, to the vacuum level. This value varies across materials, with metals typically showcasing high work functions ranging from 2 to 5 eV, attributed to their densely populated Fermi levels.
Semiconductors, on the other hand, display dynamic work functions due to the varying nature of their Fermi levels influenced by factors such as doping and temperature changes.
When a metal and a semiconductor come into contact, they seek equilibrium, leading to a uniform vacuum level across the junction through charge transfer, continuing until the Fermi levels of both materials align. This triggers energy band bending within the semiconductor, leading to the creation of a Schottky barrier, a potential energy barrier for electrons moving across the metal-semiconductor junction.
The Schottky barrier's height governs the conductivity of the junction and it is determined by the relationship between the metal's work function and the semiconductor's electron affinity.