Difference Between Schottky Diode and Fast Recovery Diode

Apr. 02, 2025

Schottky diodes and fast recovery diodes are both designed for high-frequency applications, offering exceptionally fast switching speeds. While they serve similar purposes, each type has distinct characteristics and advantages that make them suitable for different use cases.

Before exploring the key differences between Schottky diodes and fast recovery diodes, let's first understand their fundamental principles.

Schottky Diode

A Schottky diode is a semiconductor device characterized by a metal-semiconductor (MS) junction, which enables extremely fast switching speeds. Unlike conventional diodes, which rely on a PN junction, Schottky diodes are unipolar, meaning that only one type of majority carrier contributes to current flow. This unique structure makes them ideal for high-frequency applications, particularly in low-power RF circuits operating up to 100 GHz.

Structure & Characteristics

Schottky diodes consist of an N-type semiconductor and a metal layer, such as aluminum, tungsten, platinum, or gold. The absence of a P-type layer reduces the forward voltage drop (typically 0.4 to 0.6V) but increases reverse leakage current, making N-type semiconductors the preferred choice.

The MS junction provides very low junction capacitance, which enables an extremely fast switching speed due to a low reverse recovery time in the range of 0.1 to 10 ns. By adjusting the doping concentration of the semiconductor and selecting appropriate metal materials, the switching speed can be further optimized.

Symbol & Connections

In circuit diagrams, the Schottky diode symbol is similar to a standard diode, but with the vertical cathode bar modified into an ‘S' shape. The anode is internally connected to the metal layer, while the cathode connects to the semiconductor layer.

Fast Recovery Diode

A fast recovery diode is a specialized PN junction diode designed for rapid switching by minimizing reverse recovery time. Also known as a fast diode, it is commonly used for high-frequency rectification applications up to 100 kHz.

Structure & Characteristics

Structurally, a fast recovery diode is similar to a conventional PN junction diode, but with modifications that enhance switching speed. The key improvement comes from recombination centers embedded within the N-type semiconductor layer. Gold is often used as a recombination center, accelerating the recombination of holes (slow-moving charge carriers) that drift back into the depletion region. This process reduces carrier lifetime, allowing the depletion region to clear quickly and effectively blocking reverse current.

While the addition of gold significantly reduces recovery time, it also increases reverse leakage current, which can be a limiting factor in certain applications. However, unlike Schottky diodes, fast recovery diodes can withstand higher reverse voltages, making them suitable for applications that require both fast switching and high voltage handling capability.

Key Differences Between Schottky and Fast Recovery Diodes

The following table shows the comparison between Schottky & Fast Recovery diodes.

Schottky Diode	Fast Recovery Diode
It is a metal & semiconductor junction diode.	It is a PN junction diode with gold doping as recombination centers.
It is a unipolar diode i.e. only one type of majority carriers is used for current flow.	It is a bipolar diode both electrons and holes participate in the current flow.
It has a positive terminal or anode as metal & negative terminal or cathode as an N-type semiconductor.	Its anode terminal is a P-type semiconductor while the cathode is an N-type semiconductor
The MS junction has very thin depletion region	The PN junction has a wider depletion region.
It has lower junction capacitance.	It has relatively higher junction capacitance.
It has an ultra-high switching speed used for signals up to 100 GHz.	It has a high switching speed used for rectification of signals up to 100 kHz.
Its reverse recovery time is around a few nanoseconds to 10 ns.	Its reverse recovery time is about 10ns to 200 ns
It has a low forward voltage of around 0.4 to 0.6 ns.	It has a relatively higher forward voltage of about 1.3 to 3.6 volts.
It has higher efficiency.	It has lower efficiency.
It can withstand maximum reverse voltage up to 150 volts.	It can withstand large reverse voltages up to 1200 volts.
It is used for the rectification of high-frequency signals.	It is used for RF applications.

Key Differences Between Schottky and Fast Recovery Diodes

Definition

A Schottky diode is a semiconductor device formed by the junction of a metal and an N-type semiconductor.

A fast recovery diode is a PN junction diode with gold doping, designed to minimize reverse recovery time.

Structure

A Schottky diode consists of two layers: a metal layer and an N-type semiconductor.

A fast recovery diode is composed of two semiconductor layers: a P-type and an N-type, with gold doping in the N-layer to enhance performance.

Current Flow

A Schottky diode is a unipolar device, meaning current flow is dominated by a single type of majority carrier.

A fast recovery diode is a bipolar device, where both majority and minority carriers contribute to current flow.

Junctions

The Schottky diode has a junction between a metal such as aluminum, tungsten, Platinum gold, and an N-type semiconductor.

The junction in a fast recovery diode is a conventional PN junction between a P-type semiconductor & N-type semiconductor.

Switching Speed

A Schottky diode has an ultra-high switching speed, reaching up to 100 GHz, due to its metal-semiconductor (MS) junction, which results in a thin depletion region and low junction capacitance.

A fast recovery diode also offers high switching speed, but it is slightly slower than a Schottky diode due to the presence of recombination centers in its semiconductor structure.

Reverse Recovery Time

A Schottky diode has an extremely short reverse recovery time of just a few nanoseconds, thanks to its unipolar nature and the absence of a PN junction, which prevents charge storage.

A fast recovery diode has a longer reverse recovery time of around 100 ns, which is still significantly shorter than a conventional diode due to gold doping.

Reverse Voltage Handling

A Schottky diode has a limited reverse voltage tolerance, typically less than 150V, as its MS junction is not designed to withstand high reverse voltages.

A fast recovery diode, with its PN junction, can handle much higher reverse voltages, reaching up to 1200V.

Power Consumption

A Schottky diode operates at a low forward voltage of 0.4V to 0.6V, resulting in lower power consumption.

A fast recovery diode has a higher forward voltage of 1.3V to 1.6V, leading to greater power consumption compared to a Schottky diode.