The structure of Schottky diodes

The structure and materials of the new high-voltage SBD are different from the traditional SBD. Traditional SBD is formed by contacting metal and semiconductor. The metal material can be aluminum, gold, molybdenum, nickel, and titanium, and the semiconductor is usually silicon (Si) or gallium arsenide (GaAs). Since electrons have higher mobility than holes, in order to obtain good frequency characteristics, N-type semiconductor materials are selected as the substrate. In order to reduce the junction capacitance of the SBD and increase the reverse breakdown voltage without making the series resistance too large, a high-resistance N- thin layer is usually epitaxially on the N+ substrate. Its structure diagram, graphic symbols and equivalent circuit. CP is the tube-case parallel capacitance, LS is the lead inductance, RS is the series resistance including the semiconductor body resistance and the lead resistance, and Cj and Rj are the junction capacitance and junction resistance (both are functions of bias current and bias voltage), respectively.　As you all know, there are a lot of conductive electrons inside metal conductors. When the metal is in contact with the semiconductor (the distance between the two is only an order of magnitude of the size of an atom), the Fermi level of the metal is lower than the Fermi level of the semiconductor. At the sub-energy level corresponding to the conduction band of the semiconductor inside the metal, the electron density is less than that of the conduction band of the semiconductor. Therefore, after the two contact, electrons will diffuse from the semiconductor to the metal, so that the metal is negatively charged and the semiconductor is positively charged. Since metal is an ideal conductor, the negative charge is only distributed in a thin layer with the size of an atom on the surface. For N-type semiconductors, the donor impurity atoms that have lost electrons become positive ions, which are distributed in a larger thickness. As a result of the diffusion of electrons from the semiconductor to the metal, a space charge region, self-built electric field and potential barrier are formed, and the depletion layer is only on the side of the N-type semiconductor (all the barrier regions fall on the side of the semiconductor). The direction of the self-built electric field in the barrier region is directed from the N-type region to the metal, and the self-built field increases with thermionic emission, and the drift current opposite to the diffusion current increases, and finally reaches a dynamic equilibrium, forming a contact potential between the metal and the semiconductor Barrier, this is the Schottky barrier.

When the applied voltage is zero, the diffusion current of electrons is equal to the reverse drift current, achieving dynamic equilibrium. When a forward bias is applied (that is, a positive voltage is applied to a metal, and a negative voltage is applied to a semiconductor), the self-built field is weakened and the barrier on the semiconductor side is lowered, thus forming a positive current from the metal to the semiconductor. When a reverse bias is applied, the self-built field increases and the barrier height increases, forming a smaller reverse current from the semiconductor to the metal. Therefore, the SBD, like the PN junction diode, is a non-linear device with unidirectional conductivity.