BETC Atomic Structure & Energy Band PDF

BETC S.N.Mishra Asst. Professor KIIT Deemed to be University Atomic Structure  Atoms consist of positive charged nucleus and electrons are revolving around them in different permitted orbits.  Each orbits have 2n2 number of electrons where 'n' is orbit number.  Elec...

BETC S.N.Mishra Asst. Professor KIIT Deemed to be University Atomic Structure  Atoms consist of positive charged nucleus and electrons are revolving around them in different permitted orbits.  Each orbits have 2n2 number of electrons where 'n' is orbit number.  Electrons jump to higher orbit by gaining energy and fall back to lower orbit by emitting light or heat. Energy level & Energy band  Energy possesed by electrons in an orbit for an isolated atom is fixed and represented by energy level.  The range of energies possesed by electrons in an orbit in solids is known as energy band.  Energy Band  The range of energies possesed by valance electrons are known as Valance energy band (V.B).  The range of energy possesed by free/conduction electrons are known as conduction energy band (C.B).  The separation between conduction energy band and valance energy band is known as forbiden energy band gap (Eg). Classification of Solids  Insulator:Those materials which do not allow the flow of current through them.  Example:Glass,wood,paper etc  In this type of materials V.B are full and C.B is empty.  Energy gap is very large (nearly 15 eV)  Unit of Energy:An electron moving through 1Volt potential difference will gain some kinetic energy which is expressed in eV.  1eV=1.6×10-19 ×1V=1.6×10-19 Joule Contd...  Conductor:Those substances which easily allow the flow of current through them.  Example:copper,gold etc  A large number of free electrons are available in conduction band.  Conduction band and valance band are overllaped.  A slight potential difference across material cause the flow of carrier to constitute current in it.  Conductor shows positive temperature coefficient of resistance.  Semiconductor:Those substances which which have conductivity lies between conductor and insulator.  Example:Silicon,Germanium,GaAs,GaP  The energy gap between C.B and V.B are very less.  Very small energy is required to move electrons from V.B to C.B.  Semiconductor shows negative temperature coefficient of resistance. Band Diagram