Gap energy is fundamental quantity to investigate the optical properties of material. Gap energy can be obtained from Tauch plot base on UV-Vis data (transmittance v.s. wavelength). Somehow, the researchers use Tauch equation:
(alpha)*(h)*(nu) = A*(h*nu - Egap)^n
where:
alpha = linear absorption coefficient; h = Planck's constant; nu = frequency of light; A = the proportionality constant; Egap = gap energy; n = 1/2 for direct band gap material.
According to the equation, it is very hard for me to determine the value of A, and how to provide the plot of (alpha*h*nu) v.s. (h*nu).
Hi Putu
I suggest to try other value for n
where n may be = 0.5, 1, 1.5 or 2 depend on the transition is allowed or forbidden , direct or indirect
greeting
from T and A measurt
u calculate alpha=-lnT/t ( t thickness of film)
then you plot alpha hx nu ( where energy hnu=1240/lambda ( nm))
if your semiconductor is direct band gap you plot alpha h nu )^0.5 vs. hnu
then by extrapolation of th elinear part you get the Eg value
Dear Indrayana,
In attach a recent paper that we are recently submitted where you can found the method to obtain the bandgap.
Best regards,
Pedro Grima
If you take transmission data in thin films over a wide wavelength range 200 nm to 2200 nm, you may get interference fringes and then you can calculate absorption coefficient as a function of frequency using Swanopole method. In this case, you need not to correct your data for reflection and also you do not need to know thickness of the film. After getting your absorption coefficient data, you can use Tauc plot to calculate band gap as suggested by other colleagues. To use Swanapole method your films should be homogeneous, of uniform thickness and shoud have single phase.
Depending upon the direct or indirect bandgap of the material, the formula for Tauc plot changes.
For direct bandgap material such as HfO2 (alpha x E(hv))2 vs. E(hv)
For indirect bandgap mateiral such as TiO2 or Nb2O5 you use
(alpha x E(hv) )0.5 vs E(hv)
Next step, you have to draw a liner fit from the inflection point where d2y/dx2 = 0 of the Tauc curve. The point of intersection of the linear fit to the x-axis where y = 0 provides the optical band gap of the material.
Hi kajal
It is the absorption values that you obtained for each wavelength.
yh sure! if u check the uv data from uv-vis spectroscopy then directly u found the tau plot there is one option ...no need to claculate by this formula..otherwise the absorption values comes while taking uv..that one is the energy values...
Hi, I noticed there are two methods here:
1) by using the expression of Eg (eV) = 1240/(wavelength in nm).
2) by using tauc plot relation.
May I know is there any differences between these two types of calculation? What is the pros and cons between these two methods?
Thank you.
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