Galvani potential difference semiconductor

At the contact of two electronic conductors (metals or semiconductors— see Fig. 3.3), equilibrium is attained when the Fermi levels (and thus the electrochemical potentials of the electrons) are identical in both phases. The chemical potentials of electrons in metals and semiconductors are constant, as the number of electrons is practically constant (the charge of the phase is the result of a negligible excess of electrons or holes, which is incomparably smaller than the total number of electrons present in the phase). The values of chemical potentials of electrons in various substances are of course different and thus the Galvani potential differences between various metals and semiconductors in contact are non-zero, which follows from Eq. (3.1.6). According to Eq. (3.1.2) the electrochemical potential of an electron in... 

The overall Galvani potential difference between the bulk of the semiconductor and the bulk of the electrolyte solution can be separated into three parts ... 

From Eq. (3), the Galvani potential difference between the semiconductor and the metal, Am P, is given by... 

A more complicated example is provided by the contact of two electronic conductors, metals or semiconductors. At equilibrium the electrochemical potentials of electrons (i.e. their Fermi energies) must be equal in both bulk phases. The Galvani potential difference between them is determined by the bulk properties of the media in contact, i.e. by the difference between the chemical potentials of electrons ... 

Transfer of the charge between both phases establishes the equilihrium condition. For an n-semiconductor with excess electrons, electrons move from the conduction band to the electrolyte and a positive charge is built up in the space-charge region of the semiconductor. This leads to the build up of a positive Galvani potential difference Arp between semiconductor and electrolyte (Figure 9.2A). 

In the case of an electrode-solution interface, the thermodynamic equilibrium between the media in contact is attained by means of electron-ion exchange processes. Since the process of attaining the equilibrium is governed by charged particles, the equilibrium state is characterized by a certain potential difference between the phases. If they are in direct contact, we deal with the potential difference between two points in different media, for example, inside a semiconductor electrode and inside a solution. This potential difference is called the Galvani potential. 

It is the electrode potential

electrochemical experiments it represents a potential difference between two identical metallic contacts of an electrochemical circuit. Such a circuit, whose one element is a semiconductor electrode, is shown schematically in Fig. 2. Besides the semiconductor electrode, it includes a reference electrode whose potential is taken, conventionally, as zero in reckoning the electrode potential (for details, see the book by Glasstone, 1946). The potential q> includes potential drops across the interfaces, i.e., the Galvani potentials at contacts—metal-semiconductor interface, semiconductor-electrolyte interface, etc., and also, if current flows in the circuit, ohmic potential drops in metal, semiconductor, electrolyte, and so on. (These ohmic drops are negligibly small under experimental conditions considered below.)... 

Fig. 7.3 The relationship between the parameters work function (w), Galvani potential (( ), Volta potential ip) and surface potential (x) and work function, electron affinity (A) and ionization energy (I) for metal (left) and semiconductor (right). Evac is the energy of the electron in vacuum immediately in front of the surface. Note that the difference between I and A corresponds to the band gap (internal redox disproportionation, cf. Section 2.1.3). A and I refer to the band edges (standard states) while w refers to Ep, that is, also takes account of the configuration entropy. Please do not confuse the symbol for energy with the symbol E used in the text for EMF. Also remember that at finite temperatures local entropy eflfects are to be considered and hence the free energy must be addressed [537],...

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