Compared with PN junction devices, silicon carbide diodes are more like an ideal switch. The two most important performance indicators of Schottky diodes are its low reverse recovery charge (Qrr) and recovery softening coefficient. When the diode voltage becomes reverse biased, the low Qrr greatly shortens the time required for the turn-off process, that is, the reverse recovery time trr. The trr of the silicon carbide diode is less than 0.01 microseconds. It is easy to use in the high frequency range. Some data show that its operating frequency can reach 1 MHz (some reports also show that it can reach 100 GHz). The high softening factor will reduce the electromagnetic interference noise generated by diode turn-off and reduce the interference of commutation operation. Silicon carbide diodes also have advantages over PN junction devices because they have low forward conduction voltage and low conduction losses.
Silicon carbide diode is a metal semiconductor device made of precious metals (gold, silver, aluminum, platinum, etc.). ) A is used as a positive electrode, and N-type semiconductor B is used as a negative electrode, and a barrier layer formed on the contact surface of the two is used to have 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 a high concentration of B to a low concentration of A. Obviously, there are no holes in metal A, so there is no diffusion movement of holes from A to B. As the electrons continue to diffuse from B to A, the concentration of electrons on the surface of B gradually decreases, and the electrical neutrality of the surface is destroyed, thus forming a barrier with the electric field direction of B A. However, under the action of this electric field, the electrons in A will also produce a drift movement 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, thus forming a Schottky barrier.
The internal circuit structure of a typical silicon carbide diode is based on an N-type semiconductor on which an N epitaxial layer doped with arsenic is formed. The anode is made of molybdenum or aluminum and other materials to form a barrier layer. Silica (silicon dioxide) is used to eliminate the electric field in the edge area and improve the pressure resistance of the tube. The N-type substrate has a very small on-resistance, and its doping concentration is 100% higher than that of the H layer. A nitrogen 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 voltage is applied to both ends of the Schottky barrier (the anode metal is connected to the anode of the power supply, and the N-type substrate is connected to the cathode of the power supply), the Schottky barrier layer becomes narrower, and Its internal resistance becomes smaller. On the other hand, if a reverse bias is applied to both ends of the Schottky barrier, the Schottky barrier layer becomes wider and its internal resistance becomes larger.
The above explanations are the basic characteristics of silicon carbide diodes. I hope that reading it will be helpful to you. If you want to learn more about silicon carbide diodes, please contact customer service online or call our company's service hotline ( The upper right corner of the website) for consultation, we will be happy to provide you with quality service!