Semiconductors

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SEMICONDUCTORS:

SEMICONDUCTORS

Overview:

Overview Introduction What are P-type and N-type semiconductors?? What are Diodes? Forward Bias & Reverse Bias Characteristics Of Ideal Diode Shockley Equation I – V Characteristics of Diodes

Introduction:

Introduction Semiconductors are materials whose electrical properties lie between Conductors and Insulators. Ex : Silicon and Germanium

What are P-type and N-type ?:

What are P-type and N-type ? Semiconductors are classified in to P-type and N-type semiconductor P-type: A P-type material is one in which holes are majority carriers i.e. they are positively charged materials (++++) N-type: A N-type material is one in which electrons are majority charge carriers i.e. they are negatively charged materials (-----)

Diodes:

Diodes Electronic devices created by bringing together a p -type and n -type region within the same semiconductor lattice. Used for rectifiers, LED etc

Diodes:

Diodes It is represented by the following symbol, where the arrow indicates the direction of positive current flow.

Forward Bias and Reverse Bias:

Forward Bias and Reverse Bias Forward Bias : Connect positive of the Diode to positive of supply…negative of Diode to negative of supply Reverse Bias: Connect positive of the Diode to negative of supply…negative of diode to positive of supply.

Characteristics of Diode:

Characteristics of Diode Diode always conducts in one direction. Diodes always conduct current when “Forward Biased” ( Zero resistance) Diodes do not conduct when Reverse Biased (Infinite resistance)

Rectification:

Rectification Converting ac to dc is accomplished by the process of rectification. Two processes are used: Half-wave rectification; Full-wave rectification.

Half-wave Rectification:

Half-wave Rectification Simplest process used to convert ac to dc. A diode is used to clip the input signal excursions of one polarity to zero.

Shockley Equation:

Shockley Equation I s is the saturation current ~10 -14 V d is the diode voltage n – emission coefficient (varies from 1 - 2 ) k = 1 . 38 × 10 –23 J/K is Boltzmann’s constant q = 1 . 60 × 10 –19 C is the electrical charge of an electron. At a temperature of 300 K, we have