Conduction bands, schematic

Fig. 1. Schematic diagram of semiconductor materials showing band gaps where CB and VB represent the conduction band and valence band, respectively and 0 and 0, mobile charge. The height of the curve represents the probabiUty of finding an electron with a given momentum bound to an N-isoelectronic impurity, (a) Direct band gap the conduction band minimum, F, is located where the electrons have 2ero momentum, ie, k = 0. The couples B—B, D—A, B—D, and B—A represent the various routes for radiative recombination. See text, (b) Indirect band gap the conduction band minimum, X, is located...

Fig. 2. Schematic diagram of active layer stmctures employed in LEDs under forward bias showing the conduction band (CB) and valence band (VB). The simplest devices employ (a) a homostmcture active layer wherein the bandgap is constant throughout the device. More advanced stmctures consist of (b) single and (c) double heterostmctures. Heterostmctures faciUtate the confinement and injection of carriers in the active region where the carriers may...

Fig. 6. Schematic of band gap energy. Eg, for the three types of electronic and ionic conductors. For electronic conductors the comparison is made of the relative occupancy of valence and conduction bands. For ionic conductors, the bands correspond to the relative occupancy of ionic sublattices. For (a),...

Figure 1 Schematic diagram of iuminescence transitions between the conduction band...

A simplified schematic diagram of transitions that lead to luminescence in materials containing impurides is shown in Figure 1. In process 1 an electron that has been excited well above the conduction band et e dribbles down, reaching thermal equilibrium with the lattice. This may result in phonon-assisted photon emission or, more likely, the emission of phonons only. Process 2 produces intrinsic luminescence due to direct recombination between an electron in the conduction band... 

Conjugated polymers are generally poor conductors unless they have been doped (oxidized or reduced) to generate mobile charge carriers. This can be explained by the schematic band diagrams shown in Fig. I.23 Polymerization causes the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the monomer to split into n and n bands. In solid-state terminology these are the valence and conduction bands, respectively. In the neutral forms shown in Structures 1-4, the valence band is filled, the conduction band is empty, and the band gap (Eg) is typically 2-3 eV.24 There is therefore little intrinsic conductivity. 

Figure 5.7. Schematic representation of the definitions of work function O, chemical potential of electrons i, electrochemical potential of electrons or Fermi level p = EF, surface potential %, Galvani (or inner) potential

Figure 5.20. Left Schematic of an O2 conducting solid electrolyte cell with fixed P02 and PO2 values at the porous working (W) and reference (R ) electrodes without (top) and with (bottom) ion backspillover on the gas exposed electrodes surfaces, showing also the range of spatial constancy of the electrochemical potential, PQ2-, of O2. Right Corresponding spatial variation in the electrochemical potential of electrons, ]Ie(= Ef) UWR is fixed in both cases to the value (RT/4F)ln( P02 /pc>2 ) also shown in the relative position of the valence band, Ev, and of the bottom of the conduction band, Ec, in the solid electrolyte (SE) numerical values correspond to 8 mol% Y203-stabilized-Zr02, pc>2=10 6 bar, po2=l bar and T=673 K.32 Reproduced by permission of The Electrochemical Society.

Fig. 5.20 Schematic diagram illustrating the energy levels of different-sized CdSe quantum dots and Ti02 (band positions are not drawn to scale). The injection of electrons from CdSe into Ti02 is influenced by the energy difference between the two conduction bands. [Adapted (in gray scale) from [351]]...

The parameters jj°, -rr, and i)+ as functions of es or + are schematically presented in Fig. 5 in accordance with (5). We see that when the Fermi level is displaced from bottom to top in Fig. 5 (i.e., as it moves away from the valency band and approaches the conduction band), the quantity t increases monotonically and jj+ decreases monotonically, i.e., the relative number of particles in the negatively charged state increases, and the relative number of particles in the positively charged state decreases. As to the quantity r ° characterizing the relative content of the neutral form of chemisorption, it passes through a maximum when the Fermi level is monotonically displaced. 

Figure 21. The energy band diagram (only the conduction band is shown) calculated for the silicon/electrolyte interface with a potential drop of 5 V and different radii of curvature. Ec is the conduction bandedge in the bulk and Ecs is the conduction bandedge at the surface. AE AEj, AE1/2, and AE1/5 are the possible tunneling energy ranges for different radii of curvature. The distribution of occupied states at the interface, Dred, is also schematically indicated. After Zhang.24...

Figure 2.3 shows a schematic view of the nano crystalline sensor material. It consists of single-crystalline tin-oxide grains with a typical size of 10 nm and a narrow size distribution [68]. The grains are in loose contact. The lower graph in Fig. 2.3 schematically represents the conduction band of the layer. 

Fig. 2.3. Schematic view of a porous nanocrystaUine sensing layer with a one-dimensional representation of the energetic conduction band. A inter-grain band bending, eVs, occms as a consequence of smTace phenomena, and a band bending, eVc, occurs at the grain-electrode contact. Eb denotes the minimmn conduction band energy in the bulk tin oxide, and Ep is the Fermi-energy in the electrode metal...

Fig. 2-13. Schematic electron state density distribution curves in the valence and conduction bands of silicon cc = conduction band edge level Cv = valence band edge level c, = band gap (1.1 eV for silicon) CB = conduction band V6 = valence band.

The electron transitions depicted in Fig. 10 correspond to transitions of the system between states characterized by different adsorption curves. Such adsorption curves which represent the energy of the system E as function of the distance r between the particle C and the adsorbent surface for the case when particle C is a monovalent atom are schematically depicted in Fig. 11 (3, 4)- The curve I represents adsorption on an unexcited crystal, i.e., on a crystal that does not contain free electrons and holes. Curve I represents curve I shifted a distance u upwards parallel to itseff that is, it corresponds to adsorption on an excited crystal containing a free electron (in the conduction band) and a free hole (in the valence band). Curves p and n represent the adsorption curves for, respectively, strong donor, and strong acceptor chemisorption (curve n can lie either below or above curve p). The minima of curves I, n, p, I correspond to the states OL, CbL d- pL, CpL eL, CL cL -1- pL. 

Analyses of the electronic and electron spin resonance (ESR) spectra of the radical cation and anion of polysilanes make it possible to elucidate the structure of HOMO and LUMO, because an unpaired electron in the radical anion or cation occupies HOMO or LUMO, respectively. As schematically depicted in Fig. 10, the radical ions of polysilanes show absorption bands in UV and near-IR regions [29 31]. The former band corresponds to intraband transitions between valence and conduction bands. The latter band corresponds to transitions within the valence or the conduction band [32,33]. Because the near-... 

Fig. 20. Schematic representation of the s, p, d and f partial contributions to the total energy of electrons in the conduction band of a light actinide metal. The different R s denote the radial extension of the different contributing orbitals. R (f-included) and R 2n-f refer to the equilibrium volumes when the 5 f electrons are itinerant and when they are non-binding (from Ref. 77)...

Fig. 7 a-c. Schematic representation of final state screening models for lanthanide and d-metal core level responses (a) and c)) (c.b. means conduction band). In part b), the possible situations for light and heavy actinides (before and after the Mott-Hubbard transition) are also represented... 

Fig. 6. Schematic partial density of states scheme for an NaCl-type (binary) compound (with UN as an example) with f electrons delocalized and unhybridized. Uranium is on the left and nitrogen on the right. In ascending order nitrogen valence band f-band tied to the Fermi level the d conduction band. The Fermi level is at zero on the energy scale. The unhybridized band centres, Qi, are shown on the right. This unhybridized model corresponds to the fully ionic model...

The active region of GaN lasers consists of of GaN containing several thin layers (30-40 A thick) of indium doped-GaN, In/lai-JM. The addition of indium reduces the band gap within the thin layers, so that the bottom of the conduction band is at lower energy than that in the bulk GaN. Electrons in this conduction band are effectively trapped because they need to gain energy from an external source to pass into the conduction band of the bulk GaN. Figure 8.13 illustrates schematically the bottom of the conduction band and the top of the valence band for a series of thin layers of In/lai JSl in GaN. 

Figure 6.1 Schematic band structures of solids (a) insulator (kT ,) (b) intrinsic semiconductor (kT ,) (c) and (d) extrinsic semiconductors donor and acceptor levels in n-type and p-type semiconductors respectively are shown, (e) compensated semiconductor (f) metal (g) semimetal top of the valence band lies above the bottom of the conduction band.

Fig. 96. Schematic illustration of a colloidal semiconductor. Band-gap excitation promotes electrons from the valence band (VB) to the conduction band (CB). In the absence of electron donors and/or acceptors of appropriate potential at the semiconductor surface or close to it, most of the charge-separated, conduction-band electrons (e CB) and valence-band holes (h+VB) non-pro-ductively recombine. Notice the band bending at the semiconductor interface [500]...

Fig. IGOa. Schematic structure of different types of composite particles [576]. b Schematic representation of a sandwich colloid. VB = valence band edge, CB — conduction band edge [575]...

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