Working Of Schottky Barrier Rectifier And Its Applications

The Schottky diode or Schottky Barrier Rectifier is named after the German physicist &#;Walter H. Schottky&#;, is a semiconductor diode designed with a metal by the semiconductor junction. It has a low-forward voltage drop and a very rapid switching act. In the early days of wireless, cat&#;s-whisker detectors are used and in early power applications, metal rectifiers used which can be measured primitive Schottky diodes. Despite the fact that, in today&#;s high tech electronics prospect these diodes have several applications. Actually, it is one of the oldest semiconductor devices in reality. As a metal-semiconductor device, its applications can be traced back to before where crystal detectors, cat&#;s whisker detectors and the like were all effectively Schottky barrier diodes.

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Schottky Barrier Rectifier?

The Schottky Barrier rectifier diode is an electronic component that is generally used in RF applications like a mixer or detector diode. This diode is also used in power applications like a rectifier because of its features like its low forward voltage drop important to lower levels of power loss contrasted to normal PN junction diodes.

The symbol of the Schottky diode is similar to the basic diode circuit symbol. This diode symbol is distinguished from other kinds of the diode by the adding of the two additional legs on the bar on the symbol.

Construction of Schottky Barrier Diode

In this diode, connection created between metal and semiconductor to form Schottky barrier i.e. metal side performs as an anode and n-type semiconductor works as a cathode. The selection of the combination of the metal and semiconductor decides the forward voltage of the diode. Both p-type and n-type semiconductor can increase Schottky barriers but p-type semiconductor has a low forward voltage contrast to the n-type semiconductor.

As we know that, a forward voltage is inversely proportional to outflow current that is if this voltage is low then the reverse outflow current is high which is not preferable. That&#;s why we are using n-type semiconductor material in this diode. Typical metals used in the assembly of Schottky barrier diode are platinum, tungsten or chromium, molybdenum, palladium silicide, platinum silicide, gold etc.

Working of Schottky Barrier Diode

As shown in the below figure, when the voltage is applied to the diode in such a way that the metal is +Ve with respect to the semiconductor. It is a unipolar device as it has electrons as majority charge carriers on both sides of the junction. When these two are brought in contact, electrons begin to flow in both directions across the metal-semiconductor interface.

Therefore there are no depletion region shapes near the junction that is, there is no large current from the metal to the semiconductor in reverse bias. Due to the time of electron-hole recombination, the delay there in the junction diodes is not present. N-type semiconductors have superior potential energy as a contrast to electrons of metals. The voltage increased across the diode will be against the built-in potential and makes simple to the flow of current.

Advantages and Disadvantages

Schottky diodes are used in a lot of applications where other kinds of the diode will not execute as well. They offer a number of advantages that include the following.

• Low turn-on voltage
• Fast recovery time
• Low junction capacitance
• High efficiency and High current density
• These diodes work at high frequencies.
• These diodes generate less unnecessary noise than P-N junction diode
• The main disadvantage of Schottky diode is, it generates large reverse saturation current than the p-n junction diode

V-I Characteristics

• The V-I characteristics of Schottky diode are shown in the figure below. The vertical line in the figure signifies the flow of current in the diode and the Horizontal line signifies the voltage applied across the diode.
• The V-I characteristics of this diode are approximately related to the P-N junction diode. But, the forward voltage drop of this diode is very little as contrasted to the P-N junction diode.
• The forward voltage drop of Schottky diode ranges from 0.2 to 0.3 volts whereas the forward voltage drop of silicon P-N junction diode ranges from 0.6 to 0.7 volts.
• If the forward bias voltage is superior to 0.2 or 0.3 volts, then the flow of current starts flowing through the diode.
• In this diode, the reverse saturation current happens at a very low-voltage as contrasted to the silicon diode.

Applications of Schottky Diode

Schottky diodes are used for many purposes which include the following

• Schottky diodes are used as rectifiers in high power application circuits
• Schottky diodes are used in various applications like RF, power, detect signal, logic circuits
• Schottky diodes play an essential role in GaAs circuits
• Schottky diodes used in the stand-alone PV (photovoltaic) system to stop batteries from discharging through the solar panels at nighttime as well as in the network connection system.
• Schottky diodes are used in voltage clamping applications.

Thus, this is all about Schottky Barrier Rectifiers Working and Its Applications. We hope that you have got a better understanding of this concept. Furthermore, for any doubts regarding this article or to implement any electrical projects please give your valuable suggestions in the comment section below. Here is a question for you, what is the main function of Schottky diode?

In my earlier years working on unique semiconductor devices, the last thing we wanted was to form a Schottky barrier at a metal-semiconductor interface. The resulting rectifying behavior is undesirable in many applications, but you can take advantage of this rectification between a metal and semiconductor. This type of diode is called a Schottky diode, and it finds its home in a number of important applications requiring rectification with low voltage drop.

Compared to p-n diodes, a Schottky diode provides lower voltage drop across the diode at low reverse bias. Some applications of Schottky diodes include rectifiers in switching regulators, discharge protection in power electronics, and rectifying circuits requiring high switching rate. If you&#;re planning on simulating the behavior of circuits with Schottky diodes, or any circuit with a rectifying element, pay attention to the highly nonlinear behavior of these components. Here&#;s what you need to keep in mind when designing these circuits.

What is a Schottky Diode?

A Schottky diode is sometimes called a Schottky barrier diode, or simply a barrier diode. These diodes are built by placing a metal film in contact with a semiconductor layer (normally n-type). These diodes are forward biased when the metal side is held at higher potential than the semiconductor side, and vice versa for reverse bias. Typical metals used in a Schottky diode are platinum, chromium, molybdenum, or tungsten. Certain metal silicides, such as palladium silicide and platinum silicide, are also used in Schottky diodes.

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Obviously, there must be a metal on the other side of the semiconductor layer to provide a path for charge carriers to move through the device. In a Schottky diode, two dissimilar metals are used for electrical contacts. The metal at the anode forms the rectifying junction in a Schottky diode, known as a Schottky barrier. At the cathode side, there is no rectifying junction, and the metal-semiconductor interface acts like a small resistor (called an Ohmic contact).

Schottky diode symbol and structure

Compared to a p-n diode, there is only a single Ohmic contact in a Schottky diode, while a p-n diode has two Ohmic contacts (one on each side of the device). This is one reason a Schottky diode has lower forward voltage drop than a p-n diode; voltage is only dropped across a single Ohmic contact, while the other contact in a Schottky diode provides rectification. The forward voltage drop across a Schottkey diode is ~300 mV, while it is ~600 mV in a silicon diode.

Aside from this characteristic, Schottky diodes exhibit the same behavior as standard p-n diodes when run with DC bias. If you&#;re looking to simulate these components prior to making your actual circuit, it&#;s important to note, especially with their unique recovery times and doping considerations, that SPICE models can make this easy, accurate, and advantageous for your overall design process. But, when the DC bias is switched, or when run with an AC signal, Schottky diodes have very different behavior than standard p-n diodes or Shockley diodes. 

Schottky Diode Reverse Recovery Time

One important aspect of Schottky diode behavior is its reverse recovery time when switched between the rectifying and non-rectifying states. Thanks to the metal contact in the device, a Schottkey diode has much faster reverse recovery time than a typical p-n diode. Any diode will have some capacitances at the metal contacts. In a Schottky diode, the parasitic capacitance at the metal-semiconductor interface is lesser than that at the junction in a silicon diode, thus its reverse recovery time is much faster.

The reverse recovery time in a Schottkey diode can reach as low as ~100 ps. Larger Schottkey diodes that are used in power electronics (e.g., in switched-mode power supplies) have longer reverse recovery times, usually reaching ~10 ns. Compare this with a typical fast p-n diode, where the reverse recovery time is at least ~100 ns.

This is why a Schottkey diode finds its home in switching regulators. The fast recovery time of a Schottkey diode allows it to be used with PWM frequencies reaching MHz levels. Combine this with a faster edge rate for the PWM signal, and you have a system that can run successfully at higher frequencies that fully switches off the MOSFET driver in the regulator. If a p-n diode were used in such a system, the maximum PWM frequency and edge rate would be limited by the slow reverse recovery time of the p-n diode.

Schottky Diodes for RF and Power Electronics

If the transistor in your regulator is saturating, a Schottky diode is also useful for voltage clamping, which limits the voltage applied to the base by channeling some current to the emitter/collector (or source/drain in a MOSFET). Another possible application is in a high frequency clipping circuit, where a pair of Schottky diodes in a back-to-back configuration will limit the output voltage at the reverse saturation current. This nicely limits the amplitude of a switching signal to some maximum, preventing potential damage to a downstream device.

Voltage clamping and RF detection with a Schottky diode

Smaller Schottky diodes are also important in RF detectors and mixers, which can operate up to 50 GHz. These smaller diodes are limited in the maximum voltage they can handle, but their low parasitic capacitances provide the fast switching time needed for RF detection (see the above circuit). There are many other applications that can benefit from a Schottky diode, thanks to its low forward voltage drop and fast reverse recovery time.

No matter which type of Schottky diode you&#;re building, you can accurately evaluate circuit behavior when you use the right PCB design and analysis software and a set of verified component models for your simulations. The design and simulation tools in PSpice Simulator for OrCAD and the full suite of analysis tools from Cadence are ideal for evaluating rectification, switching behavior, and other aspects of these components in a larger system. The manufacturing preparation tools also help ensure your components will be sourceable at scale.

If you&#;re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.

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