When a metal or superconductor comes into close contact with a semiconductor, the Fermi levels in both materials must be equal at thermal equilibrium. Additionally, the vacuum level must remain continuous across the interface. These two requirements lead to a unique energy band diagram for the contact, as depicted in Figure 1.
The resulting band bending at the interface creates a potential barrier known as the Schottky barrier.
The height of this barrier, denoted as ΦBn, is simply the difference between the metal work function, Φm (representing the energy difference between the metal Fermi level and the vacuum level), and the electron affinity, Χ, of the semiconductor (representing the difference between the semiconductor’s conduction band edge and the vacuum level).
The width of the Schottky barrier depends on various factors, including the doping density of the semiconductor. As a result, in the case of semiconductor-superconductor-semiconductor (SSmS) junctions, it becomes possible to adjust the barrier to allow either more or fewer electrons to tunnel through it.
In summary, the Schottky barrier forms at the interface between a metal or superconductor and a semiconductor due to the alignment of Fermi levels and the continuity of the vacuum level. The barrier height is determined by the difference between the metalwork function and the semiconductor’s electron affinity. The width of the barrier can be tuned based on the doping density of the semiconductor, enabling control over electron tunneling through the junction.
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