What are the working principles and applications of Schottky diodes?

Schottky diodes are metal-semiconductor devices made of precious metals (gold, silver, aluminum, platinum, etc.) A as the positive electrode and N-type semiconductor B as the negative electrode. Because there are a large number of electrons in N-type semiconductors, and there are only a very small number of free electrons in precious metals, electrons diffuse from B with a high concentration to A with a low concentration. Obviously, there are no holes in metal A, and there is no diffusion movement of holes from A to B. As the electrons continue to diffuse from B to A, the electron concentration on the B surface gradually decreases, and the surface electroneutrality is destroyed, so a potential barrier is formed, and its electric field direction is B→A. However, under the action of this electric field, the electrons in A will also drift from A → B, thus weakening the electric field formed due to diffusion motion. When a certain width of the space charge region is established, the electron drift motion caused by the electric field and the electron diffusion motion caused by different concentrations reach a relative equilibrium, and the Schottky barrier is formed.

　　The internal circuit structure of a typical Schottky rectifier diodee is based on an N-type semiconductor with an N-type semiconductor as a substrate on which an N-epitaxial layer with arsenic as a dopant is formed. The anode uses materials such as molybdenum or aluminum to make a barrier layer. Silica (SiO2) is used to eliminate the electric field in the edge area and increase the pressure resistance value of the diodee. N-type substrates have very small on-state resistance, and their doping concentration is 100% times higher than that of the H-layer. An N+ cathode layer is formed at the bottom of 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, as shown in the figure. 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.

　　To sum up, the structural principle of Schottky rectifier diodee is very different from PN junction rectifier diodee, usually PN junction rectifier diodee is called junction rectifier diodee, and the metal-semi-conduit rectifier diodee is called Schottky rectifier diodee, and the aluminum-silicon Schottky diode made by silicon plane process has also come out, which can not only save precious metals, greatly reduce costs, but also improve the consistency of parameters.

　　Schottky diode applications

　　The structure and characteristics of SBD make it suitable for high-frequency rectification in low-voltage and high-current output occasions, detection and mixing at very high frequencies (such as X-band, C-band, S-band and Ku-band), and clamping in high-speed logic circuits. SBD is also often used in ICs, such as SBD?TTL 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 electrical parameters of SBDs used for detection and mixing also include IF impedance (refers to the impedance of the specified IF when the rated local oscillator power is applied by the SBD, generally between 200Ω~600Ω), VSWR ratio (generally ≤2) and noise figure.

　　Schottky diode action

　　Schottky diodesSchottky diodes, also known as Schottky barrier diodes