Principle and structure of Schottky 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 internal circuit structure of a typical Schottky rectifier is based on N-type semiconductors, on which an N-epitaxial layer is formed with arsenic as a dopant. The anode (barrier layer) metal material is molybdenum. Silicon dioxide (SiO2) is used to eliminate the electric field in the edge area and improve the voltage withstand value of the diodee. The N-type substrate has a very 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, and its function is to reduce the contact resistance of the cathode. By adjusting the structure parameters, a suitable Schottky barrier can be formed between the substrate and the anode metal. When the positive bias voltage E is added, the metal An and N-type substrate B are connected to the positive and negative poles of the power supply, respectively, and the barrier width Wo becomes narrow. When the negative bias is-E, the width of the barrier increases.
To sum up, the structure principle of Schottky rectifier diodee is very different from that of PN junction rectifier diodee. Generally speaking, PN junction rectifier diodee is called junction rectifier diodee, and metal-semi-conduit rectifier diodee is called Schottky rectifier diodee. In recent years, aluminum-silicon Schottky diodes manufactured by silicon plane technology have also come out, which can not only save precious metals, greatly reduce costs, but also improve the consistency of parameters.
The Schottky rectifier diodee uses only one kind of carrier (electron) to transport charge, and there is no accumulation of excess minority carriers outside the barrier, so there is no charge storage problem (Qrr storage 0), so the switching characteristics are improved. The reverse recovery time can be reduced to less than 10ns. However, its reverse voltage withstand value is low and generally does not exceed 100V in the past tense. Therefore, it is suitable to work under the condition of low voltage and high current. Making use of the characteristic of low voltage drop, the efficiency of low voltage and high current rectifier (or continuous current) circuit can be improved.
Second, the structure of Schottky diode.
Schottky diodes are very different from PN junction diodes in structure and principle. The interior of Schottky diodes is composed of anode metal (barrier layer made of materials such as molybdenum or aluminum), SiO2 electric field elimination material, N-epitaxial layer (arsenic material), N-type silicon substrate, N + cathode layer and cathode metal, as shown in figure 4-44. A Schottky barrier is formed between the N-type substrate and the anode metal. When a forward bias voltage is added at both ends of the Schottky barrier (the anode metal is connected to the positive pole of the power supply, and the N-type substrate is connected to the negative pole of the power supply), the Schottky barrier layer becomes narrower and its internal resistance becomes smaller; on the contrary, if a reverse bias voltage is added at both ends of the Schottky barrier, the Schottky barrier layer becomes wider and its internal resistance becomes larger.
Schottky diodes are divided into two packaging forms: lead and surface mount (patch).
Schottky diodes with lead packaging are usually used as high frequency and high current rectifier diodes, continuous current diodes or protective diodes. It has two packaging forms: single-diodee and pair-diodee (double diodes).