Donor surface state

The Fermi level, e, at the surface can be derived in the same way as the interior Fermi level of extrinsic semiconductors shown in Eqns. 2-22 and 2-24 to give Eqn. 2-35 for the surface with a donor surface state at the energy level e , ... 

Band-bending and hence open-circuit voltage in Schottky barrier solar cells are favoured by an insulating layer with acceptor/ donor surface states which are in better communication with the n-type/p-type semiconductor than they are with the metal. 

Electrochemical reactions at semiconductor electrodes have a number of special features relative to reactions at metal electrodes these arise from the electronic structure found in the bulk and at the surface of semiconductors. The electronic structure of metals is mainly a function only of their chemical nature. That of semiconductors is also a function of other factors acceptor- or donor-type impurities present in bulk, the character of surface states (which in turn is determined largely by surface pretreatment), the action of light, and so on. Therefore, the electronic structure of semiconductors having a particular chemical composition can vary widely. This is part of the explanation for the appreciable scatter of experimental data obtained by different workers. For reproducible results one must clearly define all factors that may influence the state of the semiconductor. 

The kinetics of depletion of the adsorption surface states corresponding to chemisorbed donor particles characterized by ionization potential Id is described by equation... 

The solution of equation (1.95) far from, the equilibrium given either by leveling-off in Id and Ep, or with complete depletion of donor adsorption surface states makes is feasible to determine the time dependence of concentration of the charged form of adsorption surface states ... 

Indeed, in this case the formation of neutral surface compound (Me Of-) is accompanied by binding of neutral superstoichiometric Me and, therefore, decrease in concentration of donors responsible for dope electric conductivity of adsorbent. In the case when the formed surface state possesses sufficient electron affinity one can-... 

Flux depends on the product of membrane permeability of the solute times the concentration of the solute (summed over all charge state forms) at the water side of the donor surface of the membrane. This concentration ideally may be equal to the dose of the drug, unless the dose exceeds the solubility limit at the pH considered, in... 

Surface related properties are carrier trapping on intrinsic (due to surface dangling bonds) and extrinsic (related to adsorbates, including donor and acceptor) surface states, carrier recombination mediated by surface states [26], and mass transfer of acceptor and donor and products from/to bulk solution. 

Fig. 6-68. Surface states created by oovsdently adsorbed particles on semiconductor electrodes BL = bonding level in adsorption = electron donor level D ABL = antibonding level in adsorption = electron acceptor level A W. = probability density of adsorption-induced surface state.

Figure 4.1. Profile of the free energy surface along the co-ordinate of the R-X bond at zero driving force initial state R-X + electron donor final state R + X. ...

No — donors per unit volume). Thus, we obtain for the electric field strength at the interface between metal (or surface states) and photoconductor... 

Energy levels corresponding to electrons localized near the surface may also be present. These are termed surface states. For example, adsorbed ions are one type of surface state they may be of the form of donors, such as hydrogen, which yield electrons to the material, or in the form of acceptors, such as oxygen, which accept, or trap electrons from the material. In Fig. 1, surface traps of the acceptor type are shown, and it is indicated that there are two possible levels present. Other possibilities are impurity atoms at the surface, which are introduced in the preparation of the sample or diffuse from the interior during heat treatment, or nonstoichiometry of the surface layers of the compound. Surface... 

A Stern-Volmer plot obtained in the presence of donors for the stilbene isomerization has both curved and linear components. Two minimal mechanistic schemes were proposed to explain this unforeseen complexity they differ as to whether the adsorption of the quencher on the surface competes with that of the reactant or whether each species has a preferred site and is adsorbed independently. In either mechanism, quenching of a surface adsorbed radical cation by a quencher in solution is required In an analogous study on ZnS with simple alkenes, high turnover numbers were observed at active sites where trapped holes derived from surface states (sulfur radicals from zinc vacancies or interstitial sulfur) play a decisive role... 

Figure 3. Energy correlations for three different surfaces of an n-type semiconductor at the flat band potential (upper row) and at equal anodic bias (lower row) (a) plane free of surface states (b) plane with surface states of acceptor character (c) plane with surf ace states of donor character...

Electron-hole recombination velocities at semiconductor interfaces vary from 102 cm/sec for Ge3 to 106 cm/sec for GaAs.4 Our first purpose is to explain this variation in chemical terms. In physical terms, the velocities are determined by the surface (or grain boundary) density of trapped electrons and holes and by the cross section of their recombination reaction. The surface density of the carriers depends on the density of surface donor and acceptor states and the (potential dependent) population of these. If the states are outside the band gap of the semiconductor, or are not populated because of their location or because they are inaccessible by either thermal or tunneling processes, they do not contribute to the recombination process. Thus, chemical processes that substantially reduce the number of states within the band gap, or shift these, so that they are less populated or make these inaccessible, reduce recombination velocities. Processes which increase the surface state density or their population or make these states accessible, increase the recombination velocity. 

In the course of catalytic oxidation, the production rate of intermediates that finally generate CO2 and H2O is also limited by rx. Some intermediates are the chemisorbed species that form surface donors and acceptors, and the other intermediates are the excited species. Both the generation rate of carriers originated from the surface states and the production rate of the excited species is governed by rx- Thus the dependence of CTL intensity on flow velocity should agree with that of rx in the diffusion-controlled region. 

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