Semiconductor electrodes energy diagram

Fig. 8.11 Top theoretical current-potential curves at a p-type semiconductor electrode in the presence (solid curve) and absence (long-dashed curve) of a redox system with a very positive standard potential short-dashed curve, cathodic partial current for a redox system which is reduced by an electron transfer via the valence band of a semiconductor. Bottom energy diagrams for cathodic (left) and anodic (right) polarization...

Fig. 8-23. Energy diagram for a redox electron transfer via the conduction band of semiconductor electrode (a) anodic redox electron transfer, (b) cathodic redox electron transfer.

Fig. 10-3. Energy diagrams for an n-type semiconductor electrode (a) in the daik and (b) in a photoexdted state S = aqueous solution = conduction band edge level at an interface cy = valence band edge level at an interface = Fermi level of oxygen...

Fig. 10-26. Energy diagram for a cell of photoelectrolytic decomposition of water consisting of a platinum cathode and an n-type semiconductor anode of strontium titanate of which the Fermi level at the flat band potential is higher than the Fermi level of hydrogen redox reaction (snao > epM+zHj) ) he = electron energy level referred to the normal hydrogen electrode ri = anodic overvoltage (positive) of hole transfer across an n-type anode interface t = cathodic overvoltage (negative) of electron transfer across a metallic cathode interface.

Fig. 3.9 Energy diagram of the semiconductor-electrolyte interface under equilibrium, (a) The Fermi level Ep is equal to redox potential energy, Ep, redox (b) The Fermi level, Ep is equal to reference electrode energy, Ereference- (c) Potential disMbution. (d) Charge across the interface.

Fig. 5. Energy diagram of a semiconductor-electrolyte interface (a) with no external voltage (b) and (c) under the application of an external voltage. The diagram explains the pinning at the semiconductor electrode surface of the energy band edges [transition from (a) to (b)] or of the Fermi level [transition from (a) to (c)].

Fig. 4.10 Two-dimensional energy band diagram for a metal dot-coated n-type semiconductor electrode.

Fig. 6. Energy diagram of an n-type semiconductor-electrolyte interface defining the electron affinity xB and the absolute redox potential and reference electrode potential (SCE).

Figure 6 An energy diagram of the charge-transfer process at an n-type semiconductor/metal interface when an external potential (F) is applied across the semiconductor electrode. The applied potential changes the electric potential difference between the semiconductor surface and the bulk region. This perturbs the concentration of electrons at the surface of the semiconductor (ns), and a net current flows through the semiconductor/metal interface. The forward reaction represents the transfer of electrons from the semiconductor to the metal and the reverse reaction represents the injection of electrons into the semiconductor from the metal. The width of the arrows indicates schematically the relative magnitude of the current, (a) The reverse bias condition for an n-type semiconductor (V > 0). The forward reaction rate is reduced relative to its equilibrium value, while the reverse reaction rate remains constant. A net positive current exists at the electrode surface, (b) The forward bias condition (V < 0), the forward reaction rate increases compared to its equilibrium value, while the reverse reaction rate remains unaffected. A net negative current exists at the electrode surface...

Fig. 3. Distribution of charge (a) and energy diagram (b) for the n-type semiconductor/electrolyte interface Uf is the flat band potential and the band bending. The energy difference depends on the reference electrode in solution. q = -4.5 eV for the NHE. See text for other symbols.

The discussion above shows that TCV can be reasonably interpreted in the framework of known electronic states. The direct determination of interface states from TCV seems difficult because the dependence of (7° with the tip potential [78, 81] finds no simple explanation within a simple one-dimensional energy diagram. Tip-induced local modifications of the band diagram of the semiconductor may exist (see Sec. 4.2.3) which complicates the determination of energy levels. The experimental dependence of [7° on the pre-history of the electrode [78, 81] stem probably from... 

Having located the semiconductor band-edge positions (relative to either the vacuum reference or a standard reference electrode), we can also place the Fermi level of the redox system, E f, redox, on the same diagram. Energy diagrams such as those... 

Fig. 3.5 Energy diagram for a metal (or semiconductor)-redox system-reference electrode system...

Fig. 11.1 Energy level diagram for an electrochemical photovoltaic cell using an n-type semiconductor electrode...

Figure 4. Energy diagram of the interface with an external voltage applied illustrating the band-edge pinning (transition from a to b) or the Fermi-level pinning (transition from a to c) at the surface of a semiconductor electrode. The flatband case is chosen as the initial state.

FIGURE 22.6 Electron energy diagrams for an n-type semiconductor electrode in the dark (a) and in the photoexcited state (b) 8s = band edge level at the interface, eF(H+ — Fermi level of the normal hydrogen electrode reaction, Sp /ifeo) = Fermi level of the normal oxygen electrode reaction, Asph = photo potential, p p = quasi-Fermi level of photoexcited holes, and nsF = quasi-Fermi level of photoexcited electrons (nsF eF for n-type semiconductors). 

FIGURE 22.11 Energy diagrams for anodic and cathodic dissolution of compound semiconductor electrodes (a) anodic dissolution impossible, (b) anodic dissolution possible, (c) cathodic dissolution impossible, and (d) cathodic dissolution possible [16] P(redox) = Fermi level of anodic and cathodic semiconductor dissolution reactions. 

Fig. 4. Energy diagram for a bulk monocrystalline n-type semiconductor electrode in the dark, in equilibrium with a redox system that has an equilibrium potential U. The Fermi-level (Ep) and the energy of the band edges are shown as a function of distance, x, perpendicular to the surface. The electrode is depleted of majority caniers at its surface, dsc is the width of the depletion layer and is the potential drop over the depletion layer.

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