Schottky diode: what it is and what is special about it

El schottky diode is another Electronic components most interesting for electronics projects. A very particular type of diode that has some peculiarities that make it unique and practical for certain applications. Given its high switching speeds, it is also widely used in TTL logic ICs.

In this guide you will know what it is the Schottky diode, who invented it, its properties, applications, where you can buy it, etc.

What is a diode?

Un semiconductor diode It is an electronic component with 2 terminals that allows the circulation of electric current through it, but only in one direction, blocking the passage to the opposite. These properties make them very useful for various applications, such as power supplies. It can also be used for control.

There are various types of diodes, for example:

Avalanche diode or TVS, which conduct in the opposite direction when the reverse voltage exceeds the breakdown voltage.
LED diode, capable of emitting light of different colors depending on the composition. This happens when charge carriers pass the junction and emit photons.
tunnel effect diode or Esaki, that allows to amplify signals and operate at very high speeds. They can be used in environments with very low temperatures, high magnetic fields, and high radiation due to high charge concentration.
Gunn diode, similar to those of tunnel and that produce a negative resistance.
laser diode, similar to LED, but can emit a laser beam.
thermal diode, can serve as a temperature sensor, since depending on it, the voltage varies.
Photodiodes, attached to optical charge carriers, that is, sensitive to light. They can also be used as light sensors.
PIN diode, is like a normal junction, but with a central section without dopant. That is, an intrinsic layer between P and N. They are used as high-frequency switches, attenuators, or ionizing radiation detectors.
Schottky diode, this diode is the one that interests us for this article, it is a diode with contact metal that has a much lower breakdown voltage than the PN.
stabistor or forward reference diode, capable of being extremely stable in forward voltage.
varicap, a variable capacitance diode.

What is a Schottky diode?

El Schottky diode was named after the German physicist Walter Hermann Schottky., since it creates a Schottky barrier (metal-semiconductor or MS junction) instead of using a conventional semiconductor junction. For that reason, in some places you will find it under the name Schottky barrier diode or surface barrier diode.

Thanks to that union, this diode has a lower forward voltage drop than PN diode, and can be used in radio frequency (RF) and high-speed switching applications. Also, another difference with the silicon PN junction diode is that it has a typical forward voltage of 0.6 to 0.75V, while the Schottky one is 0.15 to 0.45V. That lower need for voltage is what makes them switch faster.

The drop can vary from one Schottky diode to another, since it depends on the metal used. To find out what it is, read the product manufacturer's datasheet.

Returning to the topic of the MS union, the metal is usually tungsten, chromium, platinum, molybdenum, some silicides (very common because they are cheap, abundant and have good conductivity), or also gold, while the semiconductor is usually N-type doped silicon, although there are also other compounds semiconductors. The metallic side is the anode, while the semiconductor side corresponds to the cathode.

The Schottky diode lacks depletion layer, and is classified as a unipolar semiconductor device, rather than bipolar like PNs. Also, the current will be the result of majority carriers (electrons) drifting through the diode, and as there is no P-zone, there are no minority carriers (holes), and when reverse biased, the diode conducts will stop almost instantly, throttling the flow of current.

Schottky diode operation

As to Schottky diode operation, can act in several ways depending on the polarization:

Not polarized: Without bias, the MS junction (being the N-type semiconductor), the conduction band electrons or free electrons move from the semiconductor to the metal to establish an equilibrium state. As you know, when a neutral atom gains an electron it becomes a negative ion, and when it loses it it becomes a positive ion. That will cause the metal atoms to become negative ions and those on the semiconductor side to positive, acting as depletion regions. Since the metal has many free electrons, the width over which the electrons move is negligible compared to the width within the N-type zone. This results in the built-in potential (voltage) being mainly in the N-zone. built-in voltage would be the barrier encountered by electrons in the semiconductor's conduction band when trying to pass to the metal side (only a small number of electrons flow from S to M). In order to overcome this barrier, the free electrons need an energy greater than the built-in voltage or there will be no current.
Direct polarization: When the positive terminal of the power source is connected to the metal terminal (anode) and the negative terminal to the N-type semiconductor (cathode), the Schottky diode is forward biased. That generates a large number of free electrons in M and S, but they cannot cross unless the applied voltage exceeds 0.2v, to overcome that barrier (integrated voltage). That is, the current flows.
Reverse polarization: In this case, the negative terminal of the power supply will be connected to the metal side (anode), and the positive to the N-type semiconductor (cathode). In that case, the width of the depletion region increases and the current flow is cut off. Not all current is cut off though, as there is a small leakage current flow due to thermally excited electrons in the metal. If the reverse bias voltage is increased, the electric current will gradually increase due to the weakening of the barrier. And if it reaches a certain value, a sudden increase in electrical current occurs, breaking the depletion region and damaging the Schottky diode permanently.

Advantages and disadvantages of the Schottky diode

As usual with any device or system, you always have its advantages and disadvantages. In the case of the Schottky diode they are:

Schottky Diode Advantages

Low junction capacitance: In a PN diode the depletion region is formed by stored charges and there is a capacitance. In the Schottky diode these charges are negligible.
Fast reverse recovery time: is the time that the diode takes to go from ON (conductive) to OFF (non-conductive), that is, the switching speed. This is related to the above, since in order for it to pass from one state to another, the charges stored in the depletion region must be discharged or eliminated, as they are low in the Schottky, it will pass from one phase to another faster.
high current density: another consequence of the above is that a small voltage is enough to produce a large current because the depletion zone is almost negligible.
Low forward voltage drop or low ignition voltage: It is low compared to the common PN junction diode, it is usually 0.2v to 0.3v, while PNs are usually around 0.6 or 0.7v. That is, less voltage is needed to generate current flow.
High efficiency: relative to the above, and this also implies less heat dissipation in high power circuits.
Suitable for high frequencies: Being fast, they can work well in RF applications.
Less noise: Schottky diode produces less unwanted noise than conventional diodes.

Schottky Diode Disadvantages

Compared to other bipolar diodes, the Schottky diode has only one noticeable disadvantage:

High reverse saturation current: produces a reverse saturation current greater than a PN.

Differences with a PN junction diode

For more information on what a Schottky diode can contribute to your project, you can see the previous graph with the curves of the PN silicon and GaAs diodes, and the Schottky type for those same semiconductors. The differences most notable are:

Schottky diode	PN Junction Diode
Metal-semiconductor junction type N	PN semiconductor junction.
Low forward voltage drop.	High forward voltage drop.
Low reverse recovery loss and recovery time.	High reverse recovery loss and reverse recovery time.
It is unipolar.	He is bi-polar.
The current is produced solely by the movement of electrons.	Current is produced by the movement of holes and electrons.
Switching speed.	Switching slow.

Possible applications of the Schottky diode

Schottky diodes are very common in many electronic products. Their unique properties and advantages over other diodes mean they have applications as diverse as:

For RF circuits.
as power rectifiers.
For very diverse power supplies.
In systems with solar panels to protect them from reverse charging of the batteries to which they are usually connected.
And much more…

And for this, they can be presented both independently, as embedded in ICs.

where to buy these diodes

If you need Schottky diodes for your projects or to start experimenting with them and understand them better, you can find them at various specialty electronics stores, as well as on Amazon. Here you have some recommendations:

Hardwarelibre

Schottky diode: what is it and what is special about it