Initially i have deposited CdTe on borosilicate glass substrate with particular condition using thermal evaporation and the observed spectrum is attached herewith (Figure 01). Then, i have repeated same procedure with same condition. But, i have observed a huge reduction in absorption edge gradient which is shown in Figure 02. So could you please let me know, what is the reason behind the reduction of the gradient in the absorption edge (UV-visible transmittance spectrum) of as deposited CdTe?
I first thought that the thickness would be different, but the fringe spacing is about the same. Could it be that for some reason your second layer has a much higher roughness than the first?
Obviously the two samples do not have the same properties:
- The 1st one has a good cristalline quality with the right transmittance edge at 0.8-0.85um corresponding to the bandgap of CdTe.
- The second one has a broad transmittance edge which is strong indication of broadened energy bandgap as a result of inhomogeneous cristallinity or disorder which meets the above suggestion by Thomas Meyerhöfer that this could be also surface roughness of the sample.
If so, then in my opinion, growth conditions of these two samples were not exactly the same. Something went wrong or at least differently with the second one.
Best regards.
Ferekides, C., and J. Britt. "CdTe solar cells with efficiencies over 15%." Solar Energy Materials and Solar Cells 35 (1994): 255-262.
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