schottky diode is a metal semiconductor device made of noble metal (gold, silver, aluminum, platinum, etc.) a as positive electrode and n-type semiconductor b as negative electrode. the potential barrier formed on the contact surface of the two devices has rectification characteristics. because there are a lot of electrons in n-type semiconductors and only a few free electrons in noble metals, electrons diffuse from high concentration b to low concentration a. obviously, there is no hole in metal a, so there is no hole diffusion from a to b. with the diffusion of electrons from b to a, the electron concentration on the surface of b decreases gradually, and the surface electronegativity is destroyed, thus forming a potential barrier with the electric field direction of b → a. however, under the action of this electric field, the electrons in a will drift from a to b, thus weakening the electric field formed by diffusion. when a certain width of space charge region is established, the relative balance between the electron drift motion caused by electric field and the electron diffusion motion caused by different concentration will be relatively balanced, thus forming schottky barrier.
the internal circuit structure of a typical schottky rectifier is shown in figure 1. it is based on n-type semiconductor, on which an n-epitaxial layer with arsenic as dopant is formed. the metal material of anode (barrier layer) is molybdenum. silicon dioxide (sio2) is used to eliminate the electric field in the edge area and improve the withstand voltage value of the tube. the n-type substrate has very small on-state resistance, and its doping concentration is 100% higher than that of h-layer. an n cathode layer is formed under the substrate to reduce the contact resistance of the cathode. by adjusting the structure parameters, a suitable schottky barrier can be formed between the substrate and the anode metal. when the positive bias voltage e is added, metal a and n-type substrate b are respectively connected to the positive and negative electrodes of the power supply, and the barrier width wo becomes narrower. when negative bias - e is applied, the barrier width increases, as shown in figure 2.
