Semiconductors charge distribution

The diffuse charge distribution in the semiconductor s surface layer leads to a drastically lower cell capacitance at the semiconductor-electrolyte interface. Typical... 

In conclusion to this part it seems noteworthy that in contrast to the effect of adsorption of molecular particles on electrophysical properties of oxide semiconductors, the major peculiarity of this effect for such chemically active particles as the simplest free radicals or atoms of simple gases (H2, O2, N2, CI2, etc.) is that they are considerably more chemically active concerning the impurity centres [47]. The latter are responsible for dope conductivity of oxide semiconductors. As for the influence of electric fields on their adsorption due to adsorption-induced surface charge distribution, they are of minor importance which is proved by results of the experiments on assessing field effect on adsorp-... 

The electronic charge distribution in a semiconductor varies with applied electrode potential (Uf), which in turn determines the differential capacitance at the interface [11,78]. Relating charge density and electric field, the capacitance of a space charge (or depletion) region can be quantitatively derived. For an n-type semiconductor Poissons equation can be written ... 

Memming R, Schwandt (1967) Potential and charge distribution at semiconductor electrolyte interface. Angew chem. Int Ed 6 851-861... 

The overall reaction of the photoelectrochemical cell (PEC), H2O + hv H2 -I- I/2O2, takes place when the energy of the photon absorbed by the photoanode is equal to or larger than the threshold energy of 1.23 eV. At standard conditions water can be reversibly electrolyzed at a potential of 1.23 V, but sustained electrolysis generally requires -1.5 V to overcome the impedance of the PEC. Ideally, a photoelectrochemical cell should operate with no external bias so as to maximize efficiency and ease of construction. When an n-type photoanode is placed in the electrolyte charge distribution occurs, in both the semiconductor and at the semiconductor-... 

Doping a p-type semiconductor generates fixed acceptor sites with a density Na, and an equal number of mobile carriers with an opposite charge h+, whose distribution is controlled by the local value of the potential T>(x), following the Boltzmann function so that the mobile charge distribution is given by ... 

A similar procedure can be used to determine the space charge distribution in n-type Si in the dark with a positive bias polarization so as to generate a depletion layer within the semiconductor substrate. In this case, the situation is somewhat different because the positive polarization in HF results in an anodic etching of the sample with a nonnegligible current density near 7 pA cm . Nevertheless, similar results were obtained, the components of the equivalent circuit were a capacitance of a few 10 F cm , and a resistance term ranging from 1 to 10Mf2cm for a bias potential varying from —0.1 to -1-0.9 V vs. SCE. 

Dowden (19) developed a theory of heterogeneous catalysis on the basis of electron exchanges between catalysts and adsorbates [see also Boudart (19a)]. Hauffe and Engell (20), Aigrain and Dugas (21), as well as Weisz (22), tried to relate chemisorption on semiconductors to the charge distributions in the adsorbing semiconductors. 

In metals, the concentration of mobile electrons is enormously high so that the excess charge is confined to a region very close to the surface, within atomic distances [14, 15]. In semiconductors with substantially less charge carrier density, on the other hand, a region of spatial charge distribution can be found [16, 17]. 

The potential distribution in the space chaige layer can be obtained by solving the Poisson equation for a given charge distribution. For a semiconductor/elecirolyte interface such as that shown in Fig.4.2, the potential,0(x), at a distance, x, from the semiconductor surface is given as follows ... 

Fig. 4.2 Schematic illustrations of (a) the charge distribution, (b) the charge-density distribution, (c) the potential distribution, and (d) the band bending at the semiconductor/redox electrolyte interface, assuming that no surface charge nor surface dipole is present.

Figure 8. Model for charge distribution and course of the electric potential at a semiconductor with two different adjacent surface areas in contact with an electrolyte...

This salt (NPrQn, /V-propylquinolinium) consists of tetramerized TCNQ chains. It undergoes a phase transition at 220 K which is considered to be a second-order metal-to-semiconductor transition. Optical reflectivity measurements on crystals, with the light polarized in the chain direction, indicate that the charge distribution on the TCNQ sites in the tetrads is less uniform at 100 K than at 300 K. This is as in TEA(TCNQ)2 (see Section III.A.3). However, estimation of this charge distribution from the bond lengths at 300 K [38] gives ambiguous results for this material [63]. 

Photopotential transients have also been studied [181]. The light pulse will generate a non-stationary concentration of electrons and holes analysis reveals that these separate rapidly in the depletion layer (type semiconductor) and an exponential concentration of electrons at the inner edge of the depletion layer, as discussed above. This new charge distribution will alter the potential distribution and numerical integration for an n-type wide bandgap material shows that, if... 

Fig. 1. Electrical potential (

Fig. 2. The charge distribution and energy-level diagram at an n-type semiconductor/electrolyte interface.

The charge distribution and electrolytic potential within the diffuse space charge layer in a solid electrode, as well as the capacity of this layer, can be treated in the same manner as in an electrolyte as shown by Rice (3, Verwey and Niessen (12) and Grimley (13). In the case of a semiconductor with electrons and holes, the charge distribution obeys the Boltzmann equations... 

---