Energy bandgap

Thin film photovoltaic devices (CdTe is a direct bandgap semiconductor with a bandgap energy of 1.5 eV at room temperature). 

Photocatalysts Surface area Bandgap Energy Ha evolution [pmolh ]... 

In amorphous semiconductors, information about the width of the band tail states (or disorder) may also be extracted from the optical absorption spectra. For photon energies near bandgap energy, the optical absorption coefficient of amorphous semiconductors exhibit an exponential dependence on the photon energy, following the so-called Urbach relationship ... 

Fig. 1 Left Schematic energy levels in a semiconductor. Right Bandgap energy vs lattice constant for some technologically important semiconductors...

As a well-known photocatalyst, ZnO has received much attention in the degradation and complete mineralization of environmental pollutants [109,206-208], Since ZnO has almost the same bandgap energy (3.2 eV) as TiOz, its photocatalytic capacity is anticipated to be similar to that of... 

The IR band has been ascribed to radiative recombination from the CB to a DB center [Ku6]. Such a recombination process is sensitive to changes in the CB energy only and is therefore expected to show a weaker dependence on confinement than the red PL. This interpretation, together with the observation that the increase in VB energy is about twice the increase in CB energy, as shown in Fig. 7.16, has been used to approximate the bandgap energy in micro PS, as shown in Fig. 7.13. 

A very crude model to calculate the increase in bandgap energy is the effective-mass particle-in-a-box approximation. Assuming parabolic bands and infinitely high barriers the lowest conduction band (CB) level of a quantum wire with a square cross-section of side length w is shifted by AEC compared to the value Ec of the bulk crystal [Lei, Ho3] ... 

All authors who calculated the increase in bandgap energy A EG found that the approximation of Eq. (7.6), based on an infinite energy barrier, overestimates the size dependence. A linear [Re2, Bui, De2, Hi4, Hi8] dependence between A Eq and 1/tv or a tv-147 law [Pr4] has been found to be more realistic, as shown in Fig. 7.15. In order to simulate the complicated structure of the sponge-like silicon network the band structures for wires along different crystal orientations [Fi2], as well as for wires with constrictions, have been calculated [Hi5], The calculated en-... 

Fig. 7.15 I ncrease in bandgap energy AEc with decreasing diameter of a silicon cluster or dot (open symbols) or a silicon wire (filled symbols), as predicted by various theoretical investigations.

The increase in bandgap energy AEG shows an approximately linear dependence on 1/iu... 

Bandgap Energies of Some Semiconductors (see Figure below)... 

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