Do you know what a Schottky diode is?

The Schottky diode is named after its inventor, Dr. Schottky, and SBD is the abbreviation for Schottky Barrier Diode (Schottky Barrier Diode, abbreviated as SBD). SBD is not made by using the principle of forming a PN junction between a P-type semiconductor and an N-type semiconductor, but by using the principle of a metal-semiconductor junction formed by contact between a metal and a semiconductor. Therefore, SBD is also called a metal-semiconductor (contact) diode or a surface barrier diode, which is a hot carrier diode.

Schottky diodes are metal-semiconductor devices made of precious metals (gold, silver, aluminum, platinum, etc.) A as the anode and N-type semiconductor B as the cathode. The barrier formed on the contact surface of the two has rectification characteristics. Because there are a large number of electrons in N-type semiconductors and only a very small amount of free electrons in precious metals, electrons diffuse from the high concentration of B to the low concentration of A. Obviously, there are no holes in metal A, and there is no diffusion movement of holes from A to B. As electrons continue to diffuse from B to A, the electron concentration on the surface of B gradually decreases, and the surface neutrality is destroyed, so a potential barrier is formed, and the direction of the electric field is B→A. However, under the action of this electric field, the electrons in A will also move from A to B, thereby weakening the electric field formed by the diffusion movement. When a space charge region with a certain width is established, the drifting movement of electrons caused by the electric field and the diffusion movement of electrons caused by different concentrations reach a relative balance, forming a Schottky barrier.

The internal circuit structure of a typical Schottky rectifier is based on an N-type semiconductor, and an N-epitaxial layer with arsenic as a dopant is formed on it. The anode uses materials such as molybdenum or aluminum to make a barrier layer. Use silicon dioxide (SiO2) to eliminate the electric field in the edge area and improve the withstand voltage of the tube. The N-type substrate has a small on-state resistance, and its doping concentration is 100% higher than that of the H-layer. An N+ cathode layer is formed under the substrate, and its function is to reduce the contact resistance of the cathode. By adjusting the structural parameters, a Schottky barrier is formed between the N-type substrate and the anode metal, as shown in Figure 1. When a forward bias is applied to both ends of the Schottky barrier (the anode metal is connected to the positive electrode of the power supply, and the N-type substrate is connected to the negative electrode of the power supply), the Schottky barrier layer becomes narrower and its internal resistance becomes smaller; on the contrary, if When reverse bias is applied to both ends of the Schottky barrier, the Schottky barrier layer becomes wider and its internal resistance becomes larger.

In summary, the structure principle of Schottky rectifier is very different from PN junction rectifier. PN junction rectifier is usually called junction rectifier, while metal-half-conductor rectifier is called Schottky rectifier. , Al-Si Schottky diodes manufactured using silicon planar technology have also come out, which not only saves precious metals, greatly reduces costs, but also improves the consistency of parameters.