Semiconductor
These are those material whose electric conductivity at room temperature line in between that of the insulator and conductor. A semiconductor in an extremely pure form is known as intrinsic semiconductor. If a measured and small amount of chemical impurity IS added to intrinsic semiconductor, it is called Extrinsic semiconductor or doped semiconductor.
External semiconductor are of two types
(1) An extrinsic semiconductor in which electrons are majority charge carrier is called H type semiconductor.
(i) An extrinsic semiconductor in which holes are the majority charge carrier is called p-type semiconductor.
Semiconductor Diode
A p-n junction is obtained by joining a small p-type crystal with a small n-type crystal without employing any other binding materials in between them. Whenever, a p-n junction is formed, electrons from region diffuse through the junction into p-region and the holes from p-region diffuse into -region. It's a result of which neutrality of both NAND p-regions is disturbed and a thin layer of immobile negative charged ions appear near the junction in the p-crystal and a layer of positive ions appear near the junction in the n-crystal. This layer containing immobile ions is called the depletion layer. The potential difference developed across the p-n junction due to diffusion of electrons and holes is called the potential barrier V. The mobility of a charge carrier is defined as the Zoner Diode velocity gained by it per unit electric field.
DIODE AS A RECTIFIER
Junction diode allows current to pass only when it is forward biased. So, if an alternating voltage is applied across a diode, the current flows only in that part of the cycle, when the diode is forward biased. This property is used to rectify alternating voltages and the circuit used for this purpose is called a rectifier and the process is known as rectification. In half-wave rectifier, only one diode is used. In it, no current flow takes place and no output signal is obtained. Even during one-half cycle, the output obtained is a mixture of DC and AC.
The ripple frequency for the half-wave rectifier is the same as that of the AC input signal. In a full-wave rectifier, two p-n junction diodes have been joined in complimentary modes. In this rectifier, we obtain a continuous unidirectional current through the load resistor R. Ripple factors in full-wave rectifier AC=048 48% VDC The average output in one cycle is v=2/3.14 VO
SPECIAL PURPOSE DIODES
It is a highly doped p-r junction diode which is not damaged by high reverse current. It is always used in reverse bias in break down voltage region and is chiefly used as a voltage regulator. Diode as Voltage Regulator The following circuit is used for stabilizing voltage across a load R. The circuit consists of a series voltage-dropping circuit is used for stabilizing voltage across a load R., The Zoner diode is selected with Zoner voltage V, equal to the voltage desired across the load. The fluctuating DC input voltage may be the DC output of a rectifier. Whenever the input voltage increases, the excess voltage Operas as increased voltage across the resistance R. This causes an increase in the input current i. This increase is taken away by the Zoner diode, while the current through the load and hence the voltage across it remains constant at. Like wise, a decrease in the input voltage causes a decrease in the input current i. The current through the diode decreases correspondingly, again maintaining the load current.
Light - Emitting Diode (LED)
It is a specially designed diode made of Gasp, GAP etc. when used in forward biased, it emits characteristic, almost monochromatic light.
In reverse biased. It works like a normal diode. 1-V Characteristics of LED LEDs are current dependent devices with its forward voltage drop (V) depending on the forward biased LED current. Light - emitting diode. Before, LED can 'emit' any form of light it needs a current to flow through it, as it is a current dependent device with their light output intensity being directly proportional to the forward current flowing through the LED.
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