The mass of electron in free space differes from the massin solid, due to different energy levels or bands. The mass in solid is represented by effective mass. It is denoted by Me* or Mn*.
Naturally an individual atom has orbitals of different energy levels which can be represented by wave functions. When the atoms are brought together, their antibonding atoms diminisles and bonding orbitals form a band of energy.
Electrons are fermions, which satisfy the exclusion principle. So, it maintains the Fermi-Dirac distribution. Where, K is Boltzmann’s constant. K=1.38×10 -23 J/K Or K=8.62×10 -5 eV/K T is absolute temperature. E F is Fermi level. Let, E=E F So that, f(E)= ½ So E F is the Fermi energy level at which the PDF is ½ . If T=0K the distribution takes the simple rectangular, shown in figure.
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