Basic principles of Schottky diodes

Basic principles of Schottky diodes

Schottky barrier diode SBD for short Schottky diode is a low-power, high-current, ultra-high-speed semiconductor device that has emerged in recent years. Its reverse recovery time is extremely short, the forward voltage drop is only about 0.4V, while the rectified current can reach several thousand amperes. These excellent characteristics are unmatched by fast recovery diodes. Most of the small and medium power Schottky rectifier diodes are packaged.

Schottky diodes are "metal semiconductor junction" diodes with Schottky characteristics. Its forward starting voltage is low. In addition to tungsten materials, the metal layer can also be made of gold, molybdenum, nickel, titanium and other materials. Its semiconductor materials are silicon or gallium arsenide, and most of them are type semiconductors. This kind of device is conducted by majority carriers, so its reverse saturation current is much larger than that of a PN junction that conducts by minority carriers. Since the storage effect of the minority carriers in the Schottky diode is very small, its frequency response is only limited by the RC time constant. Therefore, it is an ideal device for high-frequency and fast switching.

Schottky diodes use the barrier formed by the contact between metal and semiconductor to control the current. Its main feature is that it has a lower forward voltage drop; in addition, it has multiple sons participating in conduction, which has a faster response speed than a minority son device. Schottky diodes are commonly used in gate circuits as clamping diodes for the collector of the triode to prevent the triode from being saturated and reducing the switching speed.

A Schottky diode is a metal-semiconductor device made of noble metal 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 electrical neutrality of the surface is destroyed, so a potential barrier is formed, and the direction of the electric field is B→A. But under the action of this electric field, the electrons in A will also produce a drifting movement from A→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 Schottky rectifier uses only one type of electron to transport charge, and there is no accumulation of excess minority carriers outside the barrier. Therefore, there is no charge storage problem, and the switching characteristics are significantly improved. Its reverse recovery time has been shortened to less than 10ns. But its reverse withstand voltage is low, generally not more than 100V. Therefore, it is suitable to work under low voltage and high current conditions. Utilizing this feature of low voltage drop, the efficiency of low voltage and high current rectifier circuit can be improved.