Intrisically, TiO2 is an n type semiconductor because of oxygen vacancies in it, but due to its large optical bandgap of 3.2 eV makes it only UV light active. Therefore, with decrease in optical bandgap, it makes TiO2 visible light active from just UV light active. So now more number of electrons and holes are generated inside the CB and VB of TiO2 respectively. Mostly, doping, creating hererojunction and creating defects inside TiO2 crystal lattice is performed to enhance its conductivity further.

In case of thin films, conductivity will also depend upon the flim thickness. If the thickness is too large beyond an optimum limit, conductivity starts to decrease again because grain size of TiO2 nanoparticle will increase leading to a increase bandgap (quantum confinement effect). Therefore one has to consider overall conditions for best conductivity.

Regards.

Hello,I agree with the answer by dr. Saurav and I suggest to load Pt on TiO2 to improve the optical properties of it in low amount and determined the best type of TIO2 ... this is part of my ph.D thesis 2013.

Usually in oxide materials oxygen vacancy will increase the conductivity of that particular materials. But some times band gap may not be, I have one question band gap and conductivity simultaneously increases only for this TiO2 oxide materials, or we can obtain the same results for other oxide materials?

The conductivity of a material depend of the availability of electrons in the conduction band or Fermi level. Metal have overlapped valence of conduction band, so they are conductive. In semiconductor, the band gap small enough to excite the valence band electrons to conduction band by absorbance of photons by means of light, of other sources. So if the band gap is very small, the the conductivity will increase. for example TIO2 is has high bandgap and lower conductivity, whereas CoO has low band gap and higher conductivity. But it does not mean CoO is better material then TiO2. Usefulness will depend on the application. On the other hand, SiO2, Al2O3 are the insulator have bandgap more than 5 eV. You can also guess the band gap and conductivity of a materials by its colour. more towards white colour means higher bandgap, lower conductivity and more towards black colour is lower band gap, higher conductivity.

Anyone can suggest me research article related to this question where band gap influences conductivity

Generally, band gap energy (Eg) and the electrical conductivity are Inversely proportional. Upon various external treatment on TiO2 film (not mentioned), due to the variations in chemical bonds there may be some possibility of increased band gap energy and hence the decreased conductivity.

Dear Faruk,

Here is a useful link t your question. Preprint Absorption coefficient and optical conductivity: a quantum perspective

and

http://www.cjps.org/fileGFZKX/journal/article/cjps/2012/1/PDF/cjps20110030.pdf

Good luck.

Arbab

Dear Faruk,

Here is a new formula I recently derived for the band gap, E_g=2e^2 k/(k_B sigma) where e=electric charge, k_B Boltzman constant, k=thermal conductivity, and sigma is the electric conductivity. You may validate this formula...

Thanks.

Arbab

Dear Md. Faruk Hossain

The conductivity of as semiconductor material is given by

sigma= q un n0+ qup p0,

where mu is the mobility n0 and p0 are the electron concentration and hole concentration at thermal equilibrium. According to doping if one is majority the other will be minority and its conductivity is negligible. This is because of the mass action law p0 n0=ni^2.

So if the material is doped its conductivity will be controlled by doping and this is the strength of the semiconductors.

However if the material is intrinsic p0=n0=ni and the conductivity will be determined by the energy gap since ni^2 is proportional to exp - Eg/kT. So, as Eg increases the intrinsic material conductivity will be appreciably reduced.

For more information please refer to the book:Book Electronic devices with physical insight

Best wishes

Dear Md. Faruk Hossain . See the following useful RG link: Article Correlation between electrical conductivity—optical band gap...

Kindly see also the following useful link: https://www.nature.com/articles/s41598-019-41049-9

Also check please the following very good link: http://www.cjps.org/fileGFZKX/journal/article/cjps/2012/1/PDF/cjps20110030.pdf