Semiconductor theory

As mentioned in the introduction, before an adequate theory was developed, it was difficult to understand the experimentally determined pho-toinduced PMC signals, especially the minority carrier accumulation near the onset of photocurrents.The reason was that neither conventional solid-state semiconductor theory nor photoelectrochemical theory had taken such a phenomenon into account. But we have shown that it is real and microwave (photo)electrochemical experiments clearly confirm it. 

Fig. 4. Simplified version of Digby s semiconductor theory of biomineralization. In the arthropod (top) ions are continually diffusing out of the animal across the cuticle at different rates setting up a potential with the outer surface positive. This causes a flow of electrons leaving the inner surface rich in proteins and the outer surface with hydroxyl ions. The alkaline outer surface favors CaC03 formation. In molluscs (bottom) muscular movements cause salt flow through the periostracum followed by an alkaline reaction on the inside inducing CaC03 deposition. (After Simkiss445 )...

Note. The Debye length (LD), although not introduced into the present simplified discussion, is a parameter frequently referred to in the gas-sensor literature. It was originally introduced into ionic solution theory and later applied to semiconductor theory where it is especially applicable to semi con -ductor/metal and semiconductor/semiconductor junctions. It is a measure of the distance beyond which the disturbance at the junction has effectively no influence on the electron distribution and therefore closely related to d (see Eq. (4.49)). It is a material parameter given by LD = (j kl /e2(, )12 where cQ is the undisturbed electron concentration, essentially the extrinsic electron concentration in the case of doped n-type tin oxide, and the other symbols have their usual meaning.)... 

In chemical terms, it may be proposed that the it electrons of the first graphite layer at the surface are localized at states which are separate from the bands of the bulk. Significant contribution of these states to the double layer capacitance necessitates an overpotential which is beyond the applied potential range (limited by water electrolysis). In terms of semiconductor theory, it may be assumed that the charge carrier density at the first and probably the second graphite layer is much lower than the bulk charge density value of 6 x 1018 carriers per cm3. 

The PPV spectra of Fig. 16 show all the signatures of exciton absorption and emission, such as in typical molecular crystals. The existence of well-defined structure in the absorption spectrum is not so easily accounted for in a band-to-band absorption model. In semiconductor theory, the main source of structure is in the joint density of states, and none is predicted in one-dimensional band structure calculations (see below). However, CPs have high-energy phonons (molecular vibrations) which are known (see, e.g., RRS spectra) to be coupled to the electron states. The influence of these vibrations has not been included in previous theories of band-to-band transition spectra in the case of such wide bands [176,183]. For excitons, the vibronic structure is washed out in the case of very intense transitions, corresponding to very wide exciton bands, the strong-coupling case [168,170]. Does a similar effect occur for one-electron bands Further theoretical work would be useful. 

From semiconductor theory the concentration of conduction electrons is given by... 

Thus, when a particle jumps, it leaves behind a hole. So then, instead of saying that a transport process occurs by particles hopping along, one could equally well say that the transport processes occur by holes moving. The concept is commonplace in semiconductor theory, where the movement of electrons in the conduction band is taken as being equivalent to a movement of so-called holes in the valence band. It has in fact already been assumed at the start of the viscosity treatment (Section 5.7.1) that the viscous flow of fused salts can be discussed in terms of the momentum transferred between liquid layers by moving holes. 

Luminescence of rare earth ions can be understood, based on transitions between (almost) atomic eigenstates of the system [5.220, 5.221]. Forster and Dexter first described energy transfer between localized centers in luminescent material [5.222-5.224]. Besides orbital theory, semiconductor theory has also contributed to the understanding of radiative transitions Both band-to-band transitions and transitions involving localized donor and/or acceptor states fit within this framework. Nevertheless, there are also still open questions concerning the theoretical aspects. 

It is difficult to imagine any band theory for an amorphous chromia activated at 250°. In terms of semiconductor theory, it is difficult to imagine such large surface coverages as we observe at —78°. The close correlations which are developing between homogeneous catalysis and catalysis on chromia cannot be understood at all on the basis of semiconductor theory. 

A. Anselm, Introduction to Semiconductor Theory, Prentice-Hall Inc., New Jersey, 1981, Chapter 9. 

To determine forbidden energy gaps in a semiconductor, one can investigate how its electronic conductivity (a) varies with temperature. Semiconductor theory indicates that the logarithm of the conductivity varies linearly with the inverse temperature. The value of the energy gap, Eg, is given by the slope of the In a Vs. 1/T line. Table 5A.4 contains the values of nine runs performed in duplicate with a germanium intrinsic semiconductor. The data were obtained at the Modern Physics Laboratory of the Physics Department of the Londrina State University, under the supervision of Prof. J. Scarminio. 

Wang, S. Fundamentals of Semiconductor Theory and Device Physics Prentice-Hall, Inc. Englewood Cliffs, 1989 p. 108. 

The electronic, semiconductor, or band theory, as developed during the 1950s and early 60s, treats the catalytic surface of an oxide as a general entity. Reactions on the surface are effected by transfer of electrons into and out of the acceptor bands of a p-type semiconductor (or vice-versa for n-type donor bands). The theory showed modest success in rationalizing the hydrogenation and oxidation performance of some oxides, but is now considered inadequate for general use. However, as electron transfers are involved in such processes, the idea of acceptor bands warrants incorporation into many mechanistic interpretations, and semiconductor theory can provide useful guidelines for the selection of minor components to improve performance. 

Anselm, A.I. Introduction to Semiconductor Theory, 645 p. Mir/Prentice-Hall, Moscow/Englewood Cliffs (1982)... 

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