Case (i) Direct band gap material:
Replot the graph as (Alpha*h*nu)^2 vs h*nu. Fit a straight line on the linear part and extrpolate the line to cut the x-axis.(ie.h*nu axis). This value on the x-axis will be our Optical band gap.
Case(ii) Indirect band gap material.
Same equation with power of first term 1/2 instead of 2. Repeat every thing else.
In most of the cases optical band gap will be practically equal to electrical band gap.
A small difference occurs in materials with large exciton binding energy.
Regards.
Case (i) Direct band gap material:
Replot the graph as (Alpha*h*nu)^2 vs h*nu. Fit a straight line on the linear part and extrpolate the line to cut the x-axis.(ie.h*nu axis). This value on the x-axis will be our Optical band gap.
Case(ii) Indirect band gap material.
Same equation with power of first term 1/2 instead of 2. Repeat every thing else.
In most of the cases optical band gap will be practically equal to electrical band gap.
A small difference occurs in materials with large exciton binding energy.
Regards.
Dear Rajeev if we have both direct and indirect band gap in our curve (as Ge) should we use case (i) or case (ii)
Dear sir,how to calculate alpha
How to calculate alpha
alpha is absorption coefficient na how to calculate from absorption vs wavelength
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