Presentation On Schottky Diode

Course Code:3208 Course Title : Microwave radar and satellite communication lab Presented By Salma Akter BKH F

Contents  Introduction  Characteristics of Schottky diode  Construction of Schottky diode  Working Principle of Schottky diode  V-I characteristics of Schottky diode  Reverse recovery time  Application  Advantage  Limitation  Difference between Schottky diode and PN junction diode

Introduction A Schottky Diode is a metal-semiconductor diode with a low forward voltage drop than the P-N junction diode and a very fast switching speed which is also known as a barrier diode. The Schottky diode (named after German physicist Walter H.Schottky). Symbol of Schottky diode

Characteristics of Schottky Diode:  A Schottky diode is also known as a hot carrier diode, surface barrier diode, majority carrier device or hot-electron diode.  It’s a low voltage diode the voltage drop normally ranges between 0.15 to 0.45volts.  This lower voltage drop provides higher switching speed and better system efficiency.  It can be used as a high frequency more than 300Mhz

Construction of Schottky 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. Typical metals used are molybdenum, platinum, chromium or tungsten; and the semiconductor would typically be N-type silicon. The metal side acts as the anode and N-type semiconductor acts as the cathode of the diode.

Working Principle Unbiased Schottky Diode The free electrons present inside the n-type semiconductor will move from n-type semiconductor to a metal. This results in production of equilibrium state. When free electrons moves across the junction, it provides an extra electron to the atoms present in the metal for which junction receive an extra electron. The atoms at the negative side junction lose electrons and become positive ions. On the metal junction, atoms will gain extra electrons and tries to become negative ions. Depletion region will be formed when these positive and negative ions comes together. In unbiased Schottky diode, only less number of electrons will flow from semiconductor to metal. Other electron flow is stopped due to the built in voltage. Forward Biased Schottky Diode when positive terminal of the battery is connected to metal and negative terminal is connected to n-type conductor, it is called as Forward biased Schottky diode. On the diode, when forward bias voltage is applied, more electrons are formed in the metal and conductor. When a voltage greater than 0.2 volts are applied, free electrons cannot move through the junction barrier. Due to this current will flow through diode. When voltage value increases, depletion region becomes thin and disappears. Reverse Biased Schottky Diode When the negative terminal of the battery is coupled to metal and positive terminal is connected to n-type conductor, it is called as Reverse biased Schottky diode. The width of depletion region increases. Therefore, the current flow stops. In the metal plate,there will be flow a small amount of leakage current due more excited electrons. When reverse biased voltage increases further, current also increases due to weak barrier. When abnormal increase in bias voltage takes place, electric current also increases suddenly. A device will be damaged, when the depletion region breaks down.

Rectification at high voltage Considering a normal diode At low frequency in a normal diode it is easy to cut off the negative portion but in higher frequency it is difficult to cut off the negative portion then there will be a noise. Schottky diode can operate at high frequency (>300Mhz) can operate easily and cut off the negative portion without noise. Vi=300Mhz

V-I Characteristics Of Schottky Barrier Diode  The forward voltage drop of the Schottky barrier diode is very low compared to a normal PN junction diode. The V-I characteristics of a Schottky barrier diode are very steeper compared to the V-I characteristics of normal PN junction diode due to the high concentration of current carriers.  The forward voltage drop ranges from 0.3 volts to 0.5 volts. This drop increases at the same time increasing the doping concentration of N type semiconductor.

REVERSE RECOVERY TIME The most important difference between the p-n and Schottky diode is reverse recovery time, when the diode switches from conducting to non-conducting state. Where in a p-n diode the reverse recovery time can be in the order of hundreds of nanoseconds and less than 100 ns for fast diodes, Schottky diodes do not have a recovery time, as there is nothing to recover (i.e. no charge carrier depletion region at the junction).

Application  Schottky diodes are used for the voltage clamping, clipping applications.  Used to prevention of transistor saturation due to the high current density in the Schottky diode.  Reverse current and discharge protection  Low power TTL logic, also used in logic circuits  Schottky diodes are used as general-purpose of rectifiers.  These diodes are used in radio frequency (RF) applications.  It is widely used in power supplies.  It is also used to detect signals such as radar.

Advantages of Schottky diode Low turn on voltage: The turn on voltage for the diode is between 0.2 and 0.3 volts. For a silicon diode it is against 0.6 to 0.7 volts from a standard silicon diode. Fast recovery time: A fast recovery time means a small amount of stored charge that can be used for high speed switching applications. Low junction capacitance: It occupies a very small area, after the result obtained from wire point contact of the silicon. Since the capacitance levels are very small.

Limitations Large reverse saturation current, Schottky diode produces large reverse saturation current than the p-n junction diode.

Schottky diodePN junction diode In this diode the junction is formed between the n-types semiconductor and the metal plate In this diode the junction is formed between the p-type and n-type semiconductors The forward voltage drop is low The forward voltage drop for pn junction diode is more Reverse recovery loss and reverse recovery time are very less Reverse recovery loss and reverse recovery time are very more It is a unipolar deviceIt is a bipolar device The conduction of current happens only due to the movement of electrons The conduction of current happens due to the movement of electrons and holes Difference between Schottky diode and PN junction diode:

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