Modern Semiconductor Device

Introduction to Modern Semiconductor Device

Electronic devices, diodes, transistors .. etc are made form semiconductors.The group of closely lying energy levels corresponding to an orbital is called an energy band. The band that contains valence electrons or the highest completely filled band or partially filled band of a solid is called valence band.The lowest unfilled or empty band of a solid is called conduction band. The energy gap between the valence and conduction bands i.e., the difference between the lowest energy of the conduction band and the highest energy of the valence band is called forbidden band or forbidden gap or energy gap. If the conduction and valence bands overlap , the solid is called conductor.  If the conduction and valence bands are separated by an energy gap of greater than 5 eV or the forbidden band width is greater than 5 eV, the solid is an insulator. If the forbidden band width is about 1 eV, the solid is a semiconductor. A pure semiconductor is called intrinsic semiconductor. Wen a semiconductor contains an impurity then the semiconductor is called an extrinsic semiconductor. It increases the conductivity of a semiconductor.Adding an impurity to a semiconductor is called doping. Extrinsic semiconductors are of two types (i) n - type semiconductor and (ii) p - type semiconductor.

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Modern Semiconductor devices

Diode :  Diode is a device with two electrodes. A p-n junction diode is a two terminal device made up of a semiconductor crystal. It has two terminals which act as electrodes. A diode is said to be forward - biased, when the p-side of the diode is connected to the positive terminal of a battery and the n-side of the diode is connected to the negative terminal of the battery. A diode is said to be reverse - biased , when the p-side of the diode is connected to the negative terminal of a battery and the n-side of the diode is connected to the positive terminal of the battery.

Rectifier:  Rectifier is a device that converts alternating current (ac) to direct current (dc). In a half wave rectifier, the output current which is dc flows for only half of the input ac. The maximum efficiency of a half wave rectifier is 40.6%. In a full wave rectifier, the output current which is dc flows during both the halves of the input ac. The maximum efficiency of a full wave rectifier is 81.2%.

Zener diode : Zener diode is a special type of diode that allows current in the forward direction lika a p - n junction diode but also in the reverse direction fi the voltage is larger than the rated break down voltage or Zener voltage without any damage. Zener diode is used as a voltage regulator.

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Modern Semiconductor devices (continued)


Transistor : A transistor is a three terminal device . Its three parts are (1)emitter(E), (ii) base (B) and (iii) collector (C). The emitter of a transistor is heavily doped and is of intermediate size. The base of a transistor is least doped and is of least size. The collector of a transistor is of intermediate doping level and is of largest size. The two types of a transistor are (i) n - p -n transistor and (ii) p - n - p transistor. The three configurations of a transistor are (i) common - emitter (CE) configuration,  (ii) common - base (CB) configuration and (III) common -collector (CC) configuration. A transistor is used as an amplifier.

logic gate :  A logic gate is an electronic circuit which performs a particular logical function. Logic gates are of different types depending upon the logical function performed by the gate. The different types are (i) AND gate, (ii) OR gate , (iii) NOT gate , (iv) NOR gate and (v) NAND gate.