I have developed ZnO thin film in nano rod structure on glass substrate and have calculated the absorption coefficient (α) value from absorbance value. I also have plotted ln(α) vs. photon energy (hv) curve. Now I want to calculate Urbach energy from the curve but I donot know the calculation procedure. Please help me by providing calculation procedure. Here I attach the xls file.
Dear Md. Nasrul Haque Mia,
This question was already made before in the researchgate. Please check the following link:
https://www.researchgate.net/post/How_can_I_calculate_Urbach_Energy_from_lnalpha_vs_photon_energy_curve2
Dear colleague Md. Nasrul Haque Mia
The Urbach tail or the exponential tail occurring at the absorption of most amorphous semiconductors, could be interpreted as arising from transition between localized states, if the density of states in the deep tails varies exponentially with energy, such an edge is expected Davis et al [REF] gave the following agreements as evidence against such an interpretation.
(1) The empirical relation for this tail can be represented as :
Alpha = Alpha0 exp {hν/Ec}
; Alpha0 is a constant, and Ec band tail width
(2) Urbach edges occur in many crystalline semiconductors.
(3) The temperature dependence of the slopes frequently follows the above relation at least at high temperature.
The observed exponential edges suggest that the breading is dominated by the random internal electric fields due to either to the lack of long range order or the presence of defects.
Ec can be calculated from the plot of ln(Alpha) vs. (hu) for the films represent a straight line, indicating that the absorption threshold characteristic an exponential absorption edge. The Urbach tail increases as the increasing of disorder and hence the localized states, which cause increasing of band tailing. The range of calculation is 1-2 eV of hν.
[REF] E. A. Davis and N. F. Mott, Phil. Mag. 22 (1970) 903.
Dear Md. Nasrul Haque Mia
After Your plotting the graph between ln(alpha) and h*neo you will get a straight line.
the reciprocal of this straight line gives you directly Urbach energy.
The attached paper may help you in your study
Good Luck and my regards
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