Semiconductor, band diagram

Figure C2.15.7. Generic band diagrams insulator, metal, semimetal, and semiconductor.

Calculated plots of energy bands as a function of wavevector k, known as band diagrams, are shown in figure C2.16.5 for Si and GaAs. Semiconductors can be divided into materials witli indirect and direct gaps. In direct-gap... 

Instead of plotting tire electron distribution function in tire energy band diagram, it is convenient to indicate tire position of tire Fenni level. In a semiconductor of high purity, tire Fenni level is close to mid-gap. In p type (n type) semiconductors, it lies near tire VB (CB). In very heavily doped semiconductors tire Fenni level can move into eitlier tire CB or VB, depending on tire doping type. 

Fig. 1. Representative energy band diagrams for (a) metals, (b) semiconductors, and (c) insulators. The dashed line represents the Fermi Level, and the shaded areas represent filled states of the bands. denotes the band gap of the material.

Fig. 9. Schottky barrier band diagrams (a) a rare situation where the metal work function is less than the semiconductor electron work affinity resulting in an ohmic contact (b) normal Schottky barrier with barrier height When the depletion width Wis <10 nm, an ohmic contact forms.

Tellurium Sulfide. In the hquid state, teUurium is completely miscible with sulfur. The Te—S phase diagram shows a eutectic at 105—110°C when the sulfur content is 98—99 atom % (94—98 wt %). TeUurium—sulfur aUoys have semiconductor properties (see Semiconductors). Bands attributed to teUurium sulfide [16608-21 -2] TeS, molecules have been observed. 

The theoretical models of effects of recharging of the surface on the band diagram in the surface-adjacent domain of semiconductor adsorbent accompanying adsorption have been developed. The effect of the surface band bending in semiconductor adsorbent on its electrophysical characteristics caused by transition phenomena have been studied. The theories of adsorption-caused response of above characteristics were derived for both ideal monocrystalline adsorbent [4] and monocrystal with... 

A point defect in an insulator or semiconductor is represented on band diagrams as an energy level. These energy levels can lie within the conduction or valence bands, but those of most consequence for electronic and optical properties are those that lie in the band gap. The effects of these impurities on the electronic properties of the solid will... 

A common photoelectrolysis cell structure is that of a semiconductor photoanode and metal cathode, the band diagrams of which are illustrated in Fig. 3.15 together with that of electrolyte redox couples. In Fig. 3.15(a) there is no contact between the semiconductor anode and metal cathode (no equilibrium effects communicated through the electrolyte). As seen in Fig. 3.15(b), contact between the two electrodes (no illumination) results in... 

Fig. 3.15 Energy diagram of semiconductor-metal photoelectrolysis cell, (a) No contact and no chemical potential equilibrium (b) galvanic contact in dark (c) effect of light illumination (d) effect of light illumination with bias, (e) Light illumination without bias, however in this case the semiconductor band edges straddle the redox potential for water photoelectrolysis.

Fig. 3.16 Energy diagram of semiconductor-metal photoelectrolysis cell with light illumination without bias, however in this case the semiconductor band edges straddle the redox potential for water photoelectrolysis.

Figure 1.12 illustrates these definitions. From the application and scientific points of view it is clear that knowledge of the electronic band diagram of organic semiconductors, and of any MOM in general, is mandatory. 

Materials with large E ex values would not be indicated for e.g., photovoltaic devices, since the photogeneration of charge carriers would be inefficient, but could in principle be used as light emitting diodes. Section 4.2 will show examples of the experimental determination of the band diagrams of selected organic semiconductors. El is usually obtained from o vs. T measurements, since a oc ... 

Fig. 1. Scheme of the band diagram for the contact metal/ -type semiconductor... 

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

Figure 9. Energy level diagrams showing movement of semiconductor band edges with respect to the redox potential of the electrolyte as a function of illumination...

Figure 8. Schematic representations of p-n junctions and corresponding energy band diagrams under various conditions (a) uniformly doped p-type and n-type semiconductors before junction is formed, (b) thermal equilibrium, (c) forward bias, and (d) reverse bias. Abbreviations are defined as follows Ec, electron energy at conduction band minimum E, , electron energy at valence band minimum IF, forward current Vf, forward voltage Vr, reverse voltage ...

Figure 2. UV-visible reflectance spectra of (8-2n)Na,2nAg,2Br-SOD with varying silver concentrations. Ag+/uc (a) 0 (b) 0.05 (c) 0.28 (d) 2.0 (e) 3.1 (f) 8.0 (g) bulk AgBr (h) (8-2n)Na,2nAg,2Cl-SOD, 0.1 Ag+/uc (i) (8-2n)Na,2nAg,2Br-sodalite, 0.1 Ag+/uc (j) (8-2n)Na,2nAg,21-SOD, 0.1 Ag+/uc. Note that band-gap absorptions for 8Na,2X-SOD expanded insulators peak at 192 (Cl), 208 (Br), and 214 nm (I) (Figure 2h,i,j) and parallel the order for the bulk fee NaX materials, 138 (Cl), 165 (Br), and 211nm (I), respectively, (k) Schematic band diagram for expanded AgX semiconductors (Reprinted from ref. 3. Copyright 1990 American Chemical Society.)...

It is generally accepted that three major processes limit the photoelectrochemical current in semiconductors after a bandgap excitation [76]. These processes are schematically illustrated in the band diagram shown in Fig. 3.2. The bold arrows show the desired processes for efficient water splitting PEC cell after a bandgap excitation the transport of electrons to the back contact, the transfer of the hole to the semiconductor surface and the oxidation of water at the semiconductor/electrolyte interface. The three major limiting processes are a) bulk recombination via bandgap states, or b) directly electron loss to holes in the... 

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