Energy Levels in Semiconductors and Electrolytes

The electronic structure of the semiconductor electrodes is usually described in terms of energy bands that can effectively be considered a continuum of energy levels due to the small difference in energy between adjacent molecular orbitals [66,67]. The highest energy band comprised of occupied molecular orbitals is called the 

Where Ecb and Evb are, respectively, the energy levels of the conduction and valence band edges, k (1.38 x 10 J/K) is the Boltzmann constant, and T (Kelvin scale, K) is the temperature, ityg 

As shown in Fig. 3.6, for intrinsic (undoped) semiconductors the number of holes equals the number of electrons and the Fermi energy level lies in the middle of the band gap. Impurity doped semiconductors in which the majority charge carriers are electrons and holes, respectively, are referred to as n-type and p-type semiconductors. For n-type semiconductors the Fermi level lies just below the conduction band, whereas for p-type semiconductors it lies just above the valence band. In an intrinsic semiconductor tbe equilibrium electron and bole concentrations, no and po respectively, in tbe conduction and valence bands are given by  

From equations (3.4.4) and (3.4.5) one can determine the energy difference between the energy band edges and the Fermi level [67]. 

For an n-type semiconductor, if the donor impurity concentration is much greater than the intrinsic carrier concentration, Nd nj, then no Nd. Equation (3.4.9) can then be written as 

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