Schottky diode 

Schottky diode is an electronic component made with a combination of metal and semiconductor material, so this junction component had many different characteristics compare to conventional P-N junction diode.

The name ‘SCHOTTKY’ is named after the German physicist ‘WALTER SCHOTTKY’, the Schottky diode had many specific electronic applications at wave shaping circuits, rectifier circuits and switching application circuits, etc..

Schottky diode construction details

Two Schottky diode regions

The construction of a Schottky diode is very much simple, one portion of the device is made with metal and the second portion is made with n-type semiconductor, the metal portion is the anode and the n-type semiconductor is the cathode.

Name of Schottky diode junction

The Schottky diode is a Unipolar or single junction semiconductor device as same as the conventional P-N junction diode, the Schottky diode junction is called the metal-semiconductor or ‘M-N’ junction.

The material used on Schottky diode

Construction-wise the cathode ‘SILICON’ n-type semiconductor is heavily doped and the anode is built with aluminum, platinum, or tungsten material.

Technically, due to the presents of two parts such as the metal and semiconductor region, the Schottky diode is known as the bilateral junction diode. 

Electrical characteristics depended on

The increasing doping at the n-type semiconductor region will result in decreasing the width of the depletion layer at the junction, so naturally electrical specifications of the Schottky diode are mainly dependent on the metal used at the p-type region and the amount of doping at the n-type region.  

Schottky diode symbolic representation

The symbolic representation of Schottky is much similar to the Zener diode but differently, the intermediate portion between anode and cathode will represent as the barrier, this is the reason why it is called a Schottky barrier diode or hot carrier diode.

Schottky diode working operation

The Schottky diode is made with a junction having metal-semiconductor materials, the junction barrier is called the Schottky barrier, at the normal condition the metal region is filled with conduction band electrons and the n-type region is partially doped.

As we can see from the internal structure of the Schottky diode, the current flows happened only with majority carriers, so the minority carrier didn’t produce any current flow, this is the reason why the Schottky diode has zero leakage current or reverse leakage current.

When the forward voltage passes through the Schottky diode, the higher energy level electrons at the n-type region penetrated to the metal region.

Different working conditions of Schottky diode

This particular section is used to explain about different working conditions of the Schottky diode, such as unbiased condition, forward biased condition, and reverse biased condition.

Unbiased condition of Schottky diode

At unbiased condition, the Schottky diode is in idle condition, this is because of the presents of the free electron at n-type and metal region junction.

At unbiased condition, a flow of electrons is happen from the n-type semiconductor region to the metal region, but the quantity of it is very limited and after that limit, electrons flow stopped.

Forward biased condition of Schottky diode  

When the positive terminal of the battery is connected to the anode and the negative terminal to the cathode means the forward biased condition.

As when a forward voltage is applied between Schottky diode, the current starts flowing from n-type region to metal region, and gradually the barrier between both junction breaks and current flows rapidly without limit.

Reverse biased condition of Schottky diode  

When the positive terminal is connected to the cathode and negative to the anode is called the reverse biased condition.

When a reverse voltage is applied between the Schottky diode, the width of the junction barrier increases.

Overall current flow at Schottky diode stops, but at metal junction more electrons become excited and due to these electrons a small amount of current will flows, this current is called the leakage current.

Gradually, the reverse voltage increases and the current flow also increase, the increase touches a limit, the voltage and current abnormality happened.

Then the current value exceeds the limit and damages the Schottky diode.  

Schottky diode VI characteristics curve

 

Forward voltage curve

The figure shows the VI characteristics curve of the Schottky diode, X-axis indicates the voltage, and Y-axis indicates the current.

The forward voltage characteristics of the Schottky diode are much similar to the PN junction diode, but the only difference is on the forward voltage drop value (Vf) is 0.3 to 0.5v.

The forward voltage at the Schottky barrier is formed due to the action of silicon at the Schottky diode.

Reverse voltage curve

The reverse voltage characteristics of the Schottky diode are also similar to conventional diode, as when a reverse voltage is applied to the Schottky diode.

A reverse leakage current will flow through the diode, the quantity is very much smaller.

After the voltage exceeds a particular value limit, the Schottky diode breaks down and an abnormal current starts to flow in the reverse direction.

Features of Schottky diode

1. High efficiency

The efficiency of the Schottky diode is very much higher than the common PN-junction diode.

The practical studies show that a calculated improvement of 0.3 to 0.5% at the efficiency is shown by Schottky diode at high load and high-frequency applications

2. Low forward voltage drop

The Schottky diode has 0.3 to 0.5v of forwarding voltage drop at its normal operation, this voltage value is achieved at Schottky by the action of silicon.

3. Low capacitance

The construction of Schottky diode is with a combination of metal-semiconductor material, the metal-based unipolar junction shows lower capacitance value compare with P-N junction.

4. Reverse recovery time

The reverse recovery time is the time taken by a diode switching from conducting to a non-conducting state.

The Schottky diode had a higher recovery time than the conventional P-N junction diode.

The only one recovery time limiting parameter for a Schottky diode is the junction capacitance.

For small-signal Schottky diode, type has a switching time of 100ps and for power Schottky diode it is a much more improved value of 10ns.

5. Reverse leakage current

The reverse leakage current is one of the main limitations of the Schottky diode at the operation.

The Schottky diode has low reverse voltage and with higher reverse leakage current.

The reverse voltage value of 50V or less, and a higher value of current leakage for higher-level Schottky diode.

The reverse leakage current will increase with the increase in temperature value.

6. Working temperature

The working temperature at the Schottky diode is much higher than a normal diode, around 200°C is the heat value at the diode, so at some of the higher applications, a special type of cooling methods and heat sink are implemented to reduce the heating.

7. Low profile surface-mount package

8. Integrated guard rings for stress protection

Schottky diode characteristics and applications

The application based on the Schottky diode will mainly utilize the properties such as switching or recovery time and forward voltage drop, so most of the applications we listed here need these two main features of the Schottky diode.

1. RF mixer and detector diode

The RF mixer is the most important device for wireless communication, the non-linear property of the Schottky diode is utilized at both the RF mixer and detector diode circuit.

The non-linearity at the operation of Schottky is used to create a different combination of signals.

The lower forward voltage drop value of the Schottky diode is used in RF mixer circuit applications.

2. Power rectifier circuit

The forward voltage drop value at the Schottky diode is shorter than the conventional diode, so power wastage is limited as it works as a rectifier component.

And then Schottky diode offers faster-switching speed or recovery time, due to this reason it had applications at SMPS circuits and they offer higher efficiency value.

3. SMPS circuit

Other than the switching speed and higher efficiency of the Schottky diode, the Schottky diode is used at SMPS circuits as a limiting circuit component.

4. Solar cell protection

The Schottky diode is used at the solar panel as the protection mechanism, the Schottky diode supports the panel to produce power when one of the cells are been shaded or damaged.

5. Voltage clamping circuit

The Schottky diodes are been used at voltage clamping circuits, as when the voltage reaches Schottky it channelizes the voltage into another path.

6. Clipping circuit

The Schottky diode had applications at chipping circuits, mainly at high-frequency clipping circuits, the applications such as frequency modulation utilize this technology.

7. Reverse current and discharge protection circuit
8. Sample and hold circuit applications
9. Charge control circuit
10. Schottky diodes at logic gates

The Schottky diode has more applications at digital circuits, the logic systems like transistor-transistor logic or (TTL) digital gates, utilize the property of Schottky diodes, such as higher frequency response, lower switching time, and lower power wastage.

Which are the types of Schottky diode  

The Schottky diode type classification is mainly done with the application basis, the uses such as rectifier, higher frequency detectors, mixer, and nonlinear elements.

• The Schottky diode series IN58xx is only used for rectifier applications.
• The Schottky diode series IN57xx is used as the small signal diodes.

Here we list two of the common Schottky diode type which has more applications at circuits.

1N5817 Schottky diode

• Maximum repetitive peak reverse voltage (V_RRM) is 20V
• The maximum DC blocking voltage (V_DC) is 20V
• Forward voltage drop (V_F) is 0.4V
• Capacitance (Cf) is 125pf
• High-frequency operation
• Used as rectifier circuits

1N5711 Schottky diode

• Maximum repetitive peak voltage (V_RRM) is 70V
• Power dissipation (Pd) is 430mW
• Forward voltage drop (V_F) is 0.4V
• Capacitance (Cf) is 2pf
• Small signal applications
• UHF/VHF detection circuits

Schottky diode SMD version

The Schottky diode is also available in SMD versions, main applications using SMD Schottky diodes are at rectifier-based components.

The SS1x (1A) and SS3x (3A) are the main and common SMD versions of the Schottky diode.

Schottky diode vs germanium diode

In the case of voltage drop values, both Schottky diode and germanium diode are much similar to each other, but the germanium diode doesn’t have many applications because the switching speed is much lower than any diode.

Advantages and disadvantages of Schottky diode

The Schottky diode has many applications on general-purpose circuits and higher ends circuits, so naturally compares with other diode types Schottky diode has many advantages and disadvantages.

Advantages of Schottky diode

• Low forward voltage drop value
• Low junction capacitance
• Faster recovery time
• Higher efficiency operation
• Less noise at operation
• Higher current density
• Low power consumption
• Schottky diode is much closer to an ideal diode
• Smaller physical package

Disadvantages of Schottky diode  

• They only operate at lower voltage ranges compare to PN-junction diodes
• They don’t withstand higher voltage ranges
• It is very expensive
• High reverse current
• Temperature-sensitive
• Quickly heated at normal operation