What are the characteristics of Schottky diodes different from other diodes?

2018-08-15

The SBD is not fabricated by the principle of forming a PN junction by contacting a P-type semiconductor with an N-type semiconductor, but by a metal-semiconductor junction principle formed by metal-to-semiconductor contact. Therefore, SBD is also called a metal-semiconductor (contact) diode or a surface barrier diode, which is a hot carrier diode.


The internal circuit structure of a typical Schottky rectifier is based on an N-type semiconductor on which an N- epitaxial layer using arsenic as a dopant is formed. The anode is made of a material such as molybdenum or aluminum to form a barrier layer. Silica (SiO2) is used to eliminate the electric field in the edge region and increase 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 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.


When a forward bias is applied to both ends of the Schottky barrier (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 is narrowed, and the internal resistance becomes small; When a reverse bias is applied across the Schottky barrier, the Schottky barrier layer becomes wider and its internal resistance becomes larger.


The Schottky rectifier uses only one kind of carrier (electron) to transport the charge, and there is no excess of minority carriers on the outside of the barrier. Therefore, there is no charge storage problem (Qrr→0), which makes the switching characteristics visible. improve. Its reverse recovery time can be shortened to less than 10ns. However, its reverse withstand voltage is low, generally not exceeding 100V when going. Therefore, it is suitable to work under low voltage and high current conditions. With its low dropout characteristics, the efficiency of low voltage, high current rectification (or freewheeling) circuits can be improved.


Schottky diodes are available in both leaded and surface mount (sMD) packages. Schottky diodes in leaded packages are commonly used as high frequency, high current rectifier diodes, freewheeling diodes or protection diodes. Common models are SR120, MBR1030, 1N5820, etc., and the chip package is often used for SS12.


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