Schottky Diode: V-I Characteristics, Symbol and Application
A Schottky diode have a very fast switching speed with a low forward voltage drop. the Schottky diode a slightly differ from the conventional diode, because Schottky diode has low forward voltage to the conventional silicon PN-junction diode.
What is Schottky Diode?
The Schottky diode is an electronics component. It is a metal semiconductor diode with very small junction. Due to very small junction, it has low forward voltage. Forward voltage drop across junction from 0.2v to 0.35v. this low forward voltage drop is the cause of fast switching speed and batter system efficiency. The barrier potential of Schottky diode is 0.4 volt.
The function of Schottky diode BA 157 in SMPS circuit is fast switching rectification of power supply converter inverter and freewheeling diode for diode for consumer.
It is used in various type of application like detector diode, mixer and radio frequency etc. it is useful in power because of low forward voltage drop due to this power losses become low as compare to PN junction diode. Also, it produces less unwanted noise compare to the normal p-n junction diode. Sometime it is also known as Schottky barrier diode or hot carrier diode, majority carrier device, hot-electron diode and barrier diode. it was invented by the German physicist Walter H. Schottky. It is a semiconductor diode not exactly the conventional PN junction diode. The conventional PN junction diode has two type of material but the Schottky diode has diffusion of semiconductor and metal. The metal use in this diode has high conductivity, basically the material use in Schottky diode are gold, chromium, tungsten, molybdenum, platinum, or certain silicates. Semiconductor material is silicon.
Symbol of Schottky Diode
The symbol for the Schottky barrier diode is slightly different from the conventional symbol. its metal is an anode terminal and semiconductor is cathode terminal. Symbol of Schottky diode is shown below.
Construction of Schottky Diode
The junction formed between the metal and lightly doped n-type semiconductor. That is called a unilateral junction. When metal and heavily doped semiconductor contact is present are called Ohmic bilateral contact.
When doping level of semiconductor is increased, then depletion width decreases. When the width is decreased to certain level, the charge carriers will tunnel easily through the depletion region. When the doping is very high, the junction act as a rectifier and it will become an ohmic bilateral contact.
Working of Schottky Diode
When it is in OFF condition, the electrons on the semiconductor side have a very low energy level when compared to the electrons present in the metal. When electrons cannot flow through the junction barrier is called the Schottky barrier. When diode is forward biased, electrons on N-side get sufficient energy to cross the junction and enter the metal. These electrons enter into the metal with high energy. These electrons are known as hot carriers. So the diode is called a hot-carrier diode.
Equivalent circuit diagram of Schottky diode.
Differences between Schottky and PN junction
| Schottky | PN junction |
| It is a unipolar device. | It is a bipolar device. |
| No stored charge due to the absence of holes in the metal side. | Noise is also relatively low. |
| High switching speed. | Low switching speed. |
| Reverse leakage current (IR) is larger. | Reverse leakage current (IR) of PN junction diode is low. |
| it is slightly expensive. | PN junction Low cost in price. |
| Lower barrier potential from 0.2 to 0.25 V. | Barrier potential 0.7 V (Si). |
VI characteristics of Schottky Diode
The graph of VI characteristic is similar to the PN junction except knee voltage at which the diode is start conducting. The MS (metal semiconductor) junction starts conducting from 0.4V. Due to low forward voltage, the forward current of Schottky diode can be larger the PN junction depending the type of material is used. The power is equal to the voltage time amps (P = V*I). The small drop of forward voltage, current ID will produce and lower forward power dissipation in the form of heat across the junction. This lower power losses Schottky diode becomes the good choice in low voltage and high current application. it is widely use in solar photovoltaic pannel.
The VI characteristics shows more linear non-rectifying characteristic and that is an Ohmic contact. The Ohmic contact is mostly used to connect the semiconductor wafer with external connecting pins or external circuitry of system.
Application Disadvantage and Application of Schottky Diode
Advantage
- It has a fast recovery time due to this diode is used for high-speed switching application.
- It has low turn-on voltage.
- It has low junction capacitance.
- It has voltage drop is low.
Disadvantage
- It has Reverse leakage current.
- It has Low reverse voltage rating.
Applications
There is a large Application of in electronics industry, use in various types of electronics products.
- Rectifier- It is use in rectifier circuit for convert alternating current to pulsating direct current.
- Voltage clamping – The forward voltage drop in PN junction diode of above 0.6V (Si) 0.2V (Ge) while the its voltage drop in forward region around 1mA is in the rage of 0.15 V to 0.46V which is good for voltage clamping application and protect the transistor saturation. It has higher current density.
- Reverse current and discharge protection– It has low forward voltage dope and less energy is wasted as heat. Due to this it is more efficient. In photovoltaic system to prevent discharging from battery to solar panel at night, called “blocking diodes”.
- RF mixer and detector diode– It has high switching speeds. Which is suitable for us in radio frequency application like RF mixer and detector
- In Solar cell applications, it is useful component.
- Power rectifier applications.
- Reverse current and discharge protection.
- it is used in Switched-mode power supplies.
