Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Band bending equilibrium

Assume, that there are adsorption particles with concentration Nt on the surface of semiconductor which is in adsorption equilibrium with a certain gas. A fraction of adsorption particles is charged with concentration designated as w<. Apart from them, on the surface there are various biographic surface states with concentration of the charged particles ng controlling the degree of an a priori band bending qUso-... [Pg.28]

In case of adsorption of donor particles with ionization potential Itj one can easily obtain the following expression for the equilibrium height of post-adsorption band bending... [Pg.44]

Consider the interface between a semiconductor and an aqueous electrolyte containing a redox system. Let the flat-band potential of the electrode be fb = 0.2 V and the equilibrium potential of the redox system o = 0.5 V, both versus SHE. Sketch the band bending when the interface is at equilibrium. Estimate the Fermi level of the semiconductor on the vacuum scale, ignoring the effect of dipole potentials at the interface. [Pg.94]

Figure 8.7 Tunneling through the space-charge layer at equilibrium and for an anodic overpotential. Note that the band bending is stronger after the application of the overpotential. The arrows indicate electrons tunneling through the space-charge barrier. Figure 8.7 Tunneling through the space-charge layer at equilibrium and for an anodic overpotential. Note that the band bending is stronger after the application of the overpotential. The arrows indicate electrons tunneling through the space-charge barrier.
To understand the role of the noble metal in modifying the photocatalysts we have to consider that the interaction between two different materials with different work functions can occur because of their different chemical potentials (see [200] and references therein). The electrons can transfer from a material with a high Fermi level to another with a lower Fermi level when they contact each other. The Fermi level of an n-type semiconductor is higher than that of the metal. Hence, the electrons can transfer from the semiconductor to the metal until thermodynamic equilibrium is established between the two when they contact each other, that is, the Fermi level of the semiconductor and metal at the interface is the same, which results in the formation of an electron-depletion region and surface upward-bent band in the semiconductor. On the contrary, the Fermi level of a p-type semiconductor is lower than that of the metal. Thus, the electrons can transfer from the metal to the semiconductor until thermodynamic equilibrium is established between the two when they contact each other, which results in the formation of a hole depletion region and surface downward-bent band in the semiconductor. Figure 12.6 shows the formation of semiconductor surface band bending when a semiconductor contacts a metal. [Pg.442]

Fig. 17.5 Scheme of basic processes occurring in DSSCs (a) and organic solar cells (c). (b) Band bending for an n-type semiconductor and a p-type semiconductor in equilibrium with an electrolyte. [Pg.462]

Upon immersion of the CdSe semiconductor into the electrolyte, electron exchange at the interface occurs until equilibrium is attained. At equilibrium, the Fermi level of the semiconductor is adjusted by the presence of a space charge layer at the semiconductor surface. This layer is due to the difference between the Fermi level of the semiconductor and the Fermi level of the electrolyte which is measured at the redox couple (X) The potential drop at the space charge layer and the amount of band bending also depend on the degree of Fermi level mismatch at the semiconductor-... [Pg.243]

Fig. 4.12 Diagram illustrating space charge layer formation in microcrystalline and nanocrystalline particles in equilibrium in a semiconductor-electrolyte interface. The nanoparticles are almost completely depleted of charge carriers with negligibly small band bending. Fig. 4.12 Diagram illustrating space charge layer formation in microcrystalline and nanocrystalline particles in equilibrium in a semiconductor-electrolyte interface. The nanoparticles are almost completely depleted of charge carriers with negligibly small band bending.
Measuring the flat band potential reference electrode), one may determine the position of the Fermi level F of a semiconductor on the electrode potential scale. Next, formulas (9)—(11) can be used to find (on the same scale) the position of Ec and v relative to F in the electrode bulk. For a chosen electrode potential one may determine, using (pn, the quantity and, hence, the band bending after that, the position of the band edges at the surface can easily be found. Finally, since the equilibrium potential for a given redox couple is known, the Fredox level can also be found with the help of Eq. (8). The diagrams thus constructed will often be used below. [Pg.270]

In the above, L is the hole diffusion length, t is the lifetime, p0 is the equilibrium hole density, and is the equilibrium band bending voltage. These equations are good approximations when 5 is not too small and are equivalent to that given in (2J where the exchange current parameter is used instead of the charge transfer rate constant. More accurate... [Pg.360]

In addition, the presence of surface charges leads to band bending at the semiconductor-metal interface. For /(-type semiconductors, these states are acceptor-like and the semiconductor at equilibrium may exhibit upward (negative) band bending as the surface Fermi level moves towards the charged... [Pg.212]

Fig. 9.4. Comparison of the band bending, space charge layer formation and Fermi levels (E,r) for a large particle when r = r throughout the depletion layer and equation (9.18) applies, and for a small particle when r = tv and equation (9.19) applies. The semiconductor particles are considered to be in thermodynamic equilibrium with a redox pair of Nernst... Fig. 9.4. Comparison of the band bending, space charge layer formation and Fermi levels (E,r) for a large particle when r = r throughout the depletion layer and equation (9.18) applies, and for a small particle when r = tv and equation (9.19) applies. The semiconductor particles are considered to be in thermodynamic equilibrium with a redox pair of Nernst...
At equilibrium, the Fermi energy is the same on both sides of the interface. But since this energy is not, in general, the same in the bulk of the materials before contact, relative to vacuum level, the positions of the valence- and conduction-band levels in the semiconductor must adjust band bending occurs. The two most probable cases are sketched in Fig. 23, for a p-type semiconductor, since CPs are generally so. [Pg.602]


See other pages where Band bending equilibrium is mentioned: [Pg.85]    [Pg.24]    [Pg.26]    [Pg.29]    [Pg.42]    [Pg.43]    [Pg.46]    [Pg.48]    [Pg.82]    [Pg.86]    [Pg.411]    [Pg.229]    [Pg.346]    [Pg.101]    [Pg.344]    [Pg.345]    [Pg.340]    [Pg.134]    [Pg.135]    [Pg.150]    [Pg.150]    [Pg.333]    [Pg.18]    [Pg.72]    [Pg.77]    [Pg.72]    [Pg.860]    [Pg.862]    [Pg.874]    [Pg.215]    [Pg.80]    [Pg.331]    [Pg.83]    [Pg.78]    [Pg.309]    [Pg.213]    [Pg.227]    [Pg.39]   
See also in sourсe #XX -- [ Pg.23 ]




SEARCH



Band bending

© 2024 chempedia.info