Optical absorption edge

The optical properties of amorphous solids are interesting. These solids are optically isotropic. Furthermore, the sharp features present in crystal spectra are absent in the spectra of amorphous solids even at low temperatures. The overall features in the electronic spectra of amorphous solids (broad band maxima) are, however, not unlike those of crystals, reflecting the importance of short-range order in determining these characteristics. The optical absorption edges of amorphous materials are not sharp and there is an exponential tail in the absorption coefficient (Fig. 7.13) associated with the intrinsic disorder. 

Figure 7.13 Comparison of the optical absorption edges of amorphous and crystalline AsjSj. (After Zallen et al, 1971.)...

The most unique and intriguing features of chalcogenide vitreous semiconductors are the photoinduced changes appearing as a nearly parallel shift of the optical absorption edge to lower energy (so-called photodarkening effect) after irradiation... 

The forbidden energy region in zinc oxide is generally considered to be 3.1 or 3.2 e.v. in width. This value is obtained from the optical absorption edge, which was found to be at about 3850 A. (28,29) for both single crystals and for specimens prepared in other ways. 

The bandgap of a semiconductor can also be determined photo-electrochemically [1, 2, 5, 7, 8], which is based on the fact that the wavelength corresponding to the onset of photocurrent agrees well with the optical absorption edge. For colloids and powders, diffuse reflectance spectroscopy method has been used to characterize the hematite bandgap [4]. 

Mg, Cd blueshift, redshift of optical absorption edge in dependence on Mg, Cd content [56]... 

In this formula, Eg, x and b are the optical bandgap, AIN molar fraction and bowing parameter, respectively. In order to determine this relationship, not only precise characterisation of Eg by the optical method but also precise determination of alloy composition x is quite important. The optical bandgap of AlGaN on sapphire in the whole compositional range was first reported by Yoshida et al [2] in 1982. They used optical absorption edge for determination of Eg, and x was determined by electron... 

Cody GD, Tiedje T, Abeles B, Brooks B, Goldstein Y. Disorder and the optical-absorption edge of hydrogenated amorphous silicon. Phys Rev Lett 1981 47 1480-3. 

Structure of the Repeat Units and Optical Absorption Edge of Five Non-Degenerate Ground State (NDGS) Conducting Polymers [17]... 

SnC>2 is also an n-type semiconductor with bandgap energy of 3.8 eV, which corresponds to an optical absorption edge below 330 nm. However, the CB position of SnC>2 is such that it is incapable of reducing oxygen molecules (Fig. 16.9). Therefore, in the past, semiconductors of such kind have not been considered as suitable photocatalysts that can be used individually. On the other hand, such materials may have an advantage regarding their band structures and can possibly provide another... 

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