Lecture4-Equilibrium+Carrier+Concentrations_marked

Lecture4-Equilibrium+Carrier+Concentrations_marked - ECE...

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Unformatted text preview: ECE 3040 - Dr. Ying Zhang Georgia Tech ECE 3040: Microelectronic Circuits Lecture 4 Reading: (Contd) Pierret 2.5-2.6 ECE 3040 - Dr. Ying Zhang Georgia Tech Electrons and holes have equal and opposite charges (+/- q = 1.6 x 10-19 coul) Carrier movement in a crystal Recapture mass effective electron m e ch electronic q time t velocity v force F dt dv m qE F n n = = * * , arg , , , mass effective hole m e ch electronic q time t velocity v force F dt dv m qE F p p = = * * , arg , , , ECE 3040 - Dr. Ying Zhang Georgia Tech Intrinsic semiconductors: Pure semiconductor with no significant amount of impurity of lattice defects n = p = constant = n i (intrinsic carrier concentration) n i increases with increasing T Extrinsic semiconductors (through doping the crystal to vary the conductivity of the material) Donor (such as P) adding extra electrons n-type material (n>p) Acceptor (such as B) adding extra holes p-type material (p>n) Dopant majority carrier and minority carrier Recapture ECE 3040 - Dr. Ying Zhang Georgia Tech How do electrons and holes populate the bands? Density of states: how allowed states are distributed as a function of energy level in the conduction and valence bands. Recapture eV cm States of Number unit E E E E m m E g E E E E m m E g v v p p v c c n n c = = 3 3 2 * * 3 2 * * , ) ( 2 ) ( , ) ( 2 ) ( h h ECE 3040 - Dr. Ying Zhang Georgia Tech Probability of occupation (Fermi Function) F(E) is the probability that a state at energy E is occupied 1-f(E) is the probability that a state at energy E is unoccupied Recapture ECE 3040 - Dr. Ying Zhang Georgia Tech Probability of occupation (Fermi Function) Recapture ECE 3040 - Dr. Ying Zhang Georgia Tech Probability of occupation (Fermi Function) Recapture ECE 3040 - Dr. Ying Zhang Georgia Tech Equilibrium distribution of carriers Recapture Equal numbers of electrons and holes (intrinsic) E F = E i (intrinsic Fermi level) when n-type: more electrons than holes p-type: more holes than electrons E i E i (E i ) E F close to E C E F close to E V ECE 3040 - Dr. Ying Zhang Georgia Tech Equilibrium Carrier Concentration...
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Lecture4-Equilibrium+Carrier+Concentrations_marked - ECE...

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