How exactly semiconductor metal oxide nanostructures behave as p-type semiconductor or n-type semiconductor? how these semiconducting properties can be further be improved?
Regarding these sensing materials, H2O is adsorbed on the oxide surface in molecular and hydroxyl forms. Water molecules increase the conductivity of n-type ceramics and decrease the conductivity of p-type ceramics. This observation has been explained as the donation of electrons from the chemically adsorbed water molecules to the ceramic surface. An alternative explanation suggested that the water molecules replace the previously adsorbed and ionized oxygen (O−, O2−, etc.) and consequently discharge the electrons from the ionized oxygen. Therefore, the ‘donor effect’ could result from both. The surface concentration of electrons causes the conductivity, and this style of sensing is typically called ‘electronic type.’ On the other hand, physically adsorbed water layer may be relatively proton-conductive. It is because of this observation that we conclude that the conductivity of ceramic semiconducting materials is due to the addition of both electrons and protons (ionic) at room temperature. However, at high temperatures (>100 °C) moisture cannot effectively condense on the surface. Hydrogen atoms contact the material surface (predominantly at the oxygen sites) and attract electrons. A depletion region forms initially due to adsorbed oxygen and the liberated electrons may counteract the depletion.
Dear Samiksha Sikarwar
Thank you for your response. Your expertise on metal oxide interaction with humidity is quite nice. However I am trying to know how exactly metal oxide behave as n-type semiconductor or p-type semiconductor, what is the criteria and mechanism, how defects exactly play role in generating majority charge carriers electrons in n-type semiconductor and holes in p-type semiconductor metal oxide nanostructures. Thank you for your time.
Dear Umesh Nakate. There are metals oxides with an excess of electrons in the valence band, for example, NbO2. Such a metal oxide will be a n-type semiconductor and under certain conditions its conductivity will increase with increasing temperature as the number of electrons in the valence band will increase. But there are also oxides with a smaller amount of electrons in the valence band relative to NbO2. Such metal oxides will be of the p-type. In case of their joining to a heterogeneous structure, will be obtained p-n-junction.
Welcome Dr. Umesh Nakate. I don't have any idea regarding the role played by the defects in generating majority charge carriers.
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