How can we calculate the electronic band gap of a thin film (say few hundred nm or micron) and the position of Fermi Level (both in doped and undoped film).?
Dear Dr. Mishra,
From temperature dependence of conductivity in intrinsic semiconductor, you can get difference of Ec and Ef which is known as activation energy. In intrinsic case, bandgap will be almost double of it. For accurate determination of electronic gap, however, optical measurements are required.In case of n type or p type semiconductors, band gap is same as in intrinsic case, only Fermi level moves towards conduction band in n type and towards valance band in p type semiconductors. Temperature dependence of conductivity in extrinsic range can give you the postion of Fermi level in these cases also. Go through any basic book on semiconductotrs for mathematical expressions.
Dear Monu,
For optical band gap we used Tuac equation and the diagram for :
(alpha*h*nu)^2 versus (h*nu) --> Eg
h is Plank constant and nu is frequency.
The slope line (tangent) of linear part of the curve when coincides the horizontal axis (h*nu) it defines the optical band gap.
I guess there is a similar approach for electrical bandgap.
Best, Hamidreza
Dear Monu
I agree with Dr Kumar and Hamidreza. In order to estimate the optical band gap you need to record the absortion (or transmitance) spectrum of your semiconducting film and then use the Tauc plot diagram.
For the determination of the EF you need to measure the UPS (ultraviolet photoemission) spectrum of your film. From the secondury electron cut-off you can estimate the work function (wich ih the energy difference between the fermi level and the vacuum lavel). From those measurements (absorption spectrum and UPS) you can also estimate the valence band and conduction band edges of your semiconductor.
Regards.
Maria
Dear Monu
is it possible to measure VBM with XPS and UPS and also compare ? have you tried before ?
Dear llker,
Indeed it is possible to determine the VBM using XPS and UPS.
We can also compare the two, but the obtained values would be different as the probing depth is different due to differnece in excitation energy. (~10 nm for XPS and ~4nm for UPS).
Hence, the contribution from surface states is higher in UPS compared to XPS.
You can also see my publications where i have done this.
Dear Monu
Can you please share the name-link of the specific publication so that I can check it .
thanks
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