The density of states is the main reason for the formation of band gap. There is a famous theory name "Density Functional Theory" which is used as implemented in the Cambridge Serial Total Energy Package (CASTEP)which is an ab initio molecular dynamics program in Materials Studio. Usng this theory we can calculate the band gap nature of the materials.From this calculation we readily see that the density of states affect the optical band of the metal oxide semiconductors.
Dear colleague Naseem Ahmad
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If the density of localized states is high through the gap the band tail will increase and vise versa. [1]Tauc J, editor. Amorphous and liquid semiconductors. New York: Plenum; 1976.
[2] Mott NF, Davis EA. Electronic processes in non-crystalline
materials. Oxford: Oxford University Press; 1971.
Please see the attached figure.
I wish this is useful and help you.
Yours
A. El-Denglawey
Surely DOS affects the bandgap of a metal oxide semiconductor and in tern affects the optical absorption properties. There are metal oxides like TiO2, ZnO etc which have a large bandgap of ~~3.05-3.3 eV. But once they are reduced that is formation of oxygen vacancies and change in oxidation states, the bandgap is decreased attributed to defect levels and, VB shifting upwards and conduction band tailing. These states are responsible for changing the DOS of the metal oxide.
References are:
1. Mat. Today. (2017) 20 10.1016/j.mattod.2017.09.005
2. Energy Environ. Sci., 8 (2015), pp. 3539–3544
3. Adv. Funct. Mater., 23 (2013), pp. 5444–5450
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