Working principle and characteristics of Schottky Diode

Schottky diode (SBD) is a kind of semiconductor device with low power consumption, high current and ultra-high speed. Its remarkable characteristics are that the reverse recovery time is very short (which can be as small as a few nanoseconds), the positive guide voltage drop is only about 0.4 V, but the rectified current can reach thousands of amperes. Schottky diodes are mostly used as high-frequency, low-voltage, high-current rectifier diodes, continuous current diodes, protection diodes, and also used as rectifier diodes and small signal detection diodes in microwave communication circuits. Commonly used in color TV secondary power rectifier, high-frequency power rectifier.
The Schottky SchottkyBarrierDiode is named after its inventor, Dr. Schottky (Schottky). Schottky SBD is short for Schottky barrier diode (SBD). SBD is not made by the principle of PN junction formed by the contact between P-type semiconductor and N-type semiconductor, but by the principle of metal-semiconductor junction formed by the contact between metal and semiconductor. Therefore, SBD, also known as metal-semiconductor (contact) diode or surface barrier diode, is a kind of hot carrier diode. Schottky diodes are multi-generic semiconductor devices made of precious metals (gold, silver, aluminum, platinum, etc.) An as positive electrode and N-type semiconductor B as negative electrode. 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 are diffused from high concentration B to low concentration A. Obviously, there is no hole in metal A, so there is no diffusion movement of hole from A to B. With the continuous diffusion of electrons from B to Aline B, the electron concentration on the surface of B decreases gradually, and the electrical neutrality of the surface is destroyed, so a potential barrier is formed, and the direction of the electric field is Benza. However, under the action of the electric field, the electrons in A will also drift from A to B, thus weakening the electric field formed by the diffusion motion. When the space charge region of a certain width is established, the electron drift motion caused by the electric field and the electron diffusion motion caused by different concentrations reach a relative balance, and the Schottky barrier is formed. The basic principle is that on the interface between metal and N-type silicon wafer, the current is controlled by the potential barrier formed by the contact between metal and semiconductor.
There is a fundamental difference in the rectifying principle between Schottky and PN junction. Its voltage resistance is only about 40V, and most of them are not higher than 60V, so that its application range is limited. Its specialty is that the switching speed is very fast and the reverse recovery time is very short. Therefore, switching diodes and low-voltage high-current rectifier diodes can be made. The main features of Schottky diode (SBD) are as follows:
1) forward voltage decrease: because the height of Schottky barrier is lower than that of PN junction, the threshold voltage and forward voltage drop of Schottky junction are lower than that of PN junction diode (about 0.2V).
2) Fast reverse recovery time: because SBD is a multi-carrier conductive device, there are no minority carrier lifetime and reverse recovery problems. The reverse recovery time of SBD is only the charge and discharge time of Schottky barrier capacitors, which is completely different from that of PN junction diodes. Because the reverse recovery charge of SBD is very small, the switching speed is very fast and the switching loss is very small, so it is especially suitable for high frequency applications.
3) High working frequency: because the storage effect of minority carriers in Schottky diode is very small, its frequency response is only limited by RC time constant, so it is an ideal device for high frequency and fast switching. Its working frequency can reach 100GHz.
4) low reverse voltage: because the reverse barrier of SBD is thin and breakdown is easy to occur on its surface, the reverse breakdown voltage is relatively low. Because SBD is more vulnerable to thermal breakdown than PN junction diodes, the reverse leakage current is larger than PN junction diodes. The structure and characteristics of SBD make it suitable for high frequency rectifier in low voltage and high current output, for detection and mixing in very high frequency (such as X band, C band, S band and Ku band), and as clamp in high speed logic circuits. SBD is also often used in IC, such as SBDTTL integrated circuits have long become the mainstream of TTL circuits and are widely used in high-speed computers. In addition to the characteristic parameters of ordinary PN junction diodes, the SBD electrical parameters used for detection and mixing also include intermediate frequency impedance (which refers to the impedance to the specified intermediate frequency when the rated local oscillator power is applied by the SBD, generally between 200 Ω and 600 Ω), voltage standing wave ratio (VSWR) (generally ≤ 2) and noise figure.