Show that, at , the average energy of the conduction electrons in a metal is equal to . (Hint: By definition of average , where n is the number density of charge carriers.)
The average energy of the conduction electrons in a metal is equal to at 0 K.
where n is the number of charge carriers in unit volume of the metal.
When valence electrons get excited by absorbing energy from the surroundings and then jump from the valence band to the conduction band, they become free to move within the substance. These electrons are known as conduction electrons.
The density of occupied states,
Where, N (E) is the density of the states and P (E) is the probability of state occupancy.
The density of states at a given energy level,
The number of charge carriers per unit volume,
Substituting the value of equation (1) in the given average energy equation, we can get the equation of average energy as follows:
Now, substituting the value of density of states from equation , we can get the value of average energy as follows:
(Since, the occupation probability is one for energies below the Fermi energy, we get-. )
Now, to get the value of the number of conduction electrons, we substitute the value of the equation (2) in (3) equation as follows:
Thus, using this above value in equation , we can get the average energy as follows:
Hence, the value of average energy is proportional to .
A silicon sample is doped with atoms having donor states 0.110eV below the bottom of the conduction band. (The energy gap in silicon is 1.11eV ) If each of these donor states is occupied with a probability of at , (a) is the Fermi level above or below the top of the silicon valence band and (b) how far above or below? (c) What then is the probability that a state at the bottom of the silicon conduction band is occupied?
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