Dear all!
Oxygen vacancies do raise negatively the Fermi level by increasing the negative charge in the semiconductor crystal structure. In the case of n-type semiconductors, I wonder if this change in the Fermi level may also affect the border of the conduction band and therefore change the light absorption properties.
Best wishes
Marco Uscanga
Hello Mr. Marco Antonio
you can see the following articles:
Electronic structure of Ta2O5 polymorphs: Variation trend of band gap and the role of oxygen vacancies
The presence of oxygen vacancies is found to have profound effects on the electronic properties near the Fermi level, notably the reduction of band gap and gap closure (insulator-to-metal transition).
Semiconductor metal oxide gas sensors: A review, Ananya Dey, in Materials Science and Engineering: B, 2018
9.4 Generating oxygen vacancy
Oxygen vacancies are considered to be important reactive agents for many adsorbates. So, many surface reactions are influenced by this type of point defect. Oxygen vacancy acts as direct adsorption site as well as electron donor site.
The presence of oxygen vacancy will increase the conductivity of the solid.
Fig. 7. Schematic band diagram of SnO2 bulk. Two vacancy donor level are located at two donor levels 0.03 and 0.15 eV below the conduction band [62].
Metal oxide semiconductors with highly concentrated oxygen vacancies for gas sensing materials: A review, Chao Zhang, Marc Debliquy, in Sensors and Actuators A: Physical, 2020
2-Roles of oxygen vacancy
Superconducting Materials: Conventional, Unconventional and Undetermined, Hideo Hosono, Kazuhiko Kuroki, in Physica C: Superconductivity and its Applications, 2015
2.3.2 Electron–doping by introduction of oxygen vacancy
Defects in Semiconductors, Matthew D. McCluskey, in Semiconductors and Semimetals, 2015
10.2 Oxygen vacancies
Recent advances in surface and interface design of photocatalysts for the degradation of volatile organic compounds, Qi Li, Fa-tang Li, in Advances in Colloid and Interface Science, 2020
2.1 Construction of oxygen vacancy
Electronic properties of hafnium oxide: A contribution from defects and traps, Vladimir A. Gritsenko, Damir R. Islamov, in Physics Reports, 2016
5 Summary and outlook
In principle, vacancies change the chemical composition and, therefore, interatomic distances and are therefore capable of changing the gap width. However, in semiconductors, vacancy concentrations are likely to be very low. So this effect can most likely be neglected. But vacancies are quite capable of creating local distortions and making the boundaries of the valence and conduction bands blurry. They lead to the formation of “tails” of states near the band boundaries. And this is how they affect the absorption of light.
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