Semiconductor Electronics Class 12 Notes Physics Chapter 14 - CBSE

Chapter : 14

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Term	Definition / Important Points
Classification of solids on the basis of band theory	Metals : The conduction band and valence band partly overlap each other and there is no forbidden energy gap. Electrons can easily move to conduction band. Insulators : The conduction band is empty and valence band is completely filled and forbidden gap is quite large ( ≅ 6 eV). Electrons cannot be excited from valence band. Semiconductors : There is small band gap (≅ l eV). At room temperature, some electrons can jump to conduction band.
Semiconductors	These are those solids which have conductivity and resistivity intermediate to metals and insulators.
Intrinsic Semiconductors	A doped semiconductors is known as extrinsic semiconductor. Semiconductors are doped with trivalent or pentavalent impurity to increase conductivity. Depending upon the type of doping (trivalent or pentavalent), extrinsic semiconductors are of two types: (i) n-type semiconductor : When a pure semiconductor is doped with a pentavalent impurity, we obtain a n-type semiconductor. (ii) p-type semiconductor : When a pure semiconductor is doped with a trivalent impurity, we obtain a p-type semiconductor.
Semiconductor Diode	A semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p-n junction connected to two electrical terminals.

Term	Definition / Important Points
p-n Junction Diode	When a p-type crystal is placed in contact with n-type crystal so as form one piece, the assembly thus formed is known as p-n junctions diode. Junction diode conducts current when diode is activated in forward biased whereas it offers high resistance when reverse biased. When p-side is connected to positive terminal and n-side is connected to negative terminal of the external battery, the junction diode is said to be forward biased. When n-side is connected to positive and p-side is connected to negative terminal of the external battery, the junction diode is said to be reverse biased.
I-V characteristics of a p-n junction
	The I-V characteristics of a p-n junction do not obey Ohm’s law
Knee Voltage	In forward biasing, the voltage at which the current starts to increases rapidly is known as cut-in or Knee voltage. For Germanium, it is 0.3 V while for Silicon it is 0.7 V.
Diode as a Rectifier	Rectification means conversion of alternating current into a direct current. A p-n junction can be used as rectifier because it permits current in one direction only. Rectifiers are of two types: (i) Half Wave Rectifier (ii) Full Wave Rectifier