Schottky diode Another Diodes essay of junction diode, the Schottky diodeis formed from a metal—semiconductor junction rather than a p—n junction, which reduces capacitance and increases switching speed. The curve is no longer exponential, it is asymptotic to a straight line whose slope is the bulk resistance.
Reverse bias[ edit ] If an external voltage is placed across the diode with the same polarity as the built-in potential, the depletion zone continues to act as an insulator, preventing any significant electric current flow unless electron—hole pairs are actively being created in the junction by, for instance, light; see photodiode.
Impurities are added to it to create a region on one side that contains negative charge carriers electronscalled an n-type semiconductorand a region on the other side that contains positive charge carriers holescalled a p-type semiconductor.
For each electron—hole pair recombination made, a positively charged dopant ion is left behind in the N-doped region, and a negatively charged dopant ion is created in the P-doped region.
The value is different for other diode types— Schottky diodes can be rated as low as 0. Observe the different Quasi Fermi levels for conduction band and valence band in n and p regions red curves.
Shockley diode equation[ edit ] Main article: As recombination proceeds and more ions are created, an increasing electric field develops through the depletion zone that acts to slow and then finally stop recombination. This is called the knee voltage or cut-in voltage and is equal to the barrier potential of the p-n junction.
When the n-type and p-type materials are attached together, a momentary flow of electrons occur from the n to the p side resulting in a third region between the two where no charge carriers are present.
The region around the p—n junction becomes depleted of charge carriers and thus behaves as an insulator. This is a feature of the exponential curve, and appears sharper on a current scale more compressed than in the diagram shown here.
The following equation is called the Shockley Diodes essay diode equation when n, the ideality factor, is set equal to 1: When a mobile electron recombines with a hole, both hole and electron vanish, leaving behind an immobile positively charged donor dopant on the N side and negatively charged acceptor dopant on the P side.
The diode can be modeled as an ideal diode in series with a fixed resistor. At very large reverse bias, beyond the peak inverse voltage or PIV, a process called reverse breakdown occurs that causes a large increase in current i. The shape of the curve is determined by the transport of charge carriers through the so-called depletion layer or depletion region that exists at the p—n junction between differing semiconductors.
The diode is commonly said to have a forward "threshold" voltage, above which it conducts and below which conduction stops. There is a definite forward voltage at which the diode starts to conduct significantly.
However, this is only an approximation as the forward characteristic is smooth see I-V graph above. However, the width of the depletion region called the depletion width cannot grow without limit. Shockley diode equation The Shockley ideal diode equation or the diode law named after the bipolar junction transistor co-inventor William Bradford Shockley gives the I—V characteristic of an ideal diode in either forward or reverse bias or no bias.
At larger forward currents the current-voltage curve starts to be dominated by the ohmic resistance of the bulk semiconductor. This is called the reverse bias phenomenon.
In the Zener diodethe concept of PIV is not applicable. However, this is temperature dependent, and at sufficiently high temperatures, Diodes essay substantial amount of reverse current can be observed mA or more. The boundary between these two regions, called a p—n junctionis where the action of the diode takes place.
This region is particularly important for power diodes. A Zener diode contains a heavily doped p—n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is "clamped" to a known value called the Zener voltageand avalanche does not occur.LED's are special diodes that emit light when connected in a circuit.
They are frequently used as "pilot" lights in electronic appliances to indicate whether the circuit is closed or not. A a clear (or often colored) epoxy case enclosed the heart of an LED, the semi-conductor chip. Essay about The Events That Led to the Independence of Cuba.
The Light Emitting Diodes Engineering Essay. Print Reference this. Disclaimer: This work has been submitted by a student. This is not an example of the work written by our professional academic writers.
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Historically the LED market has experienced.Download