Hi Kamal

Could you give more details about"How do you measure the band gap"?

Did you measure the band gap for si substrate alone and SiO2 alone.?

Hi Kamal

I suggest that decreasing the film thickness produce more uniform spin coated  SiO2 crystallization layer on silicon wafer leading to large band gap. Also the absorption follow the same scenario.....

Greeting 

Go thorugh this link:-

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3615571/

hello sir WESAM A A TWEJ .sir i want to ask something i m working on si substrate having coating with 6% Co doped silicon dioxide nanoparticles ,sir my question is silicon have larger bandgap of i think 8 or 9 ev ,but in my coating work its reduced to 2 ev ,what is the reason behind this ??????plz answer it .i calculated it through tauc plot relation.

Dear Kamal

I suppose that you follow sol gel technique , and using spin coating method, but you don,t say how you was measured your absorption spectra is it by means of reflection? Firstly, your calculated band gap values are within the acceptable values. However, you have to used the correct parameter for calculate the band gap such as it is indirect allowed transition. You have to take into considerations that your are work with nano composite film (nano-size effect), well, the absorption spectra sometime being perverting because of overlapping of SiO2 and CoO absorbance which have different band gaps . anyway that's all for now, I hope that you can recalculated your plots with new insight, remember that Si band gap should not contribute your composite film band-gap values. By the way the band gap of Si is 1.1 eV. The band gap (CoO) is around 2.4 eV , The band gap (SiO2) is around 9 eV

Greeting

Is band gap of 4 ev or 3.9 ev is acceptable when coated si substrate with sio2 nanoparticles?????

plz answer my question y sio2 coating is used on si substrate when sio2 cannot conduct electricity ??????????????????