The band gap results for CuSe and Ni-doped CuSe, according to the Tauc plot and the mathematical DITM (Derivation Ineffective Thickness Method) model, in which thickness and type of transition (direct or indirect) are not required for band gap calculation, are as follows. What analysis can be inferred from these results? In the Tauc plot, not all transitions are clearly observable, whereas in the DITM model, they are visible. The results are indicated in a separate table.
Milad Fallah The study reveals that Ni-doping decreases the band gap of CuSe, both fundamental and second, due to the introduction of new energy levels. The DITM method, which is more sensitive in detecting transitions than the Tauc plot, reveals the second band gap in all Ni-doped samples, making it a valuable tool for band gap analysis, especially when the Tauc plot is insufficient.
Dear Alvena Shahid,
Thank you so much for your response. I appreciate your clarification. Please let me to ask my question more in detail.
According to the Tauc model, the fundamental band gap for undoped CuSe is approximately 4 eV, slightly reduced in Ni-doped samples. Data indicates a slight decrease in the band gap with an increase in Ni concentration and deposition time. A decreasing trend in the band gap has been observed in the Tauc model, even when considering the formation of a degenerate semiconductor at higher doping levels.
On the other hand, the second band gap in the Tauc plot is not discernible for all samples, posing a limitation.
In the DITM model, there is a prominent peak around 4 eV for all doped samples. The first question is whether this peak at 4 eV represents the same fundamental band gap for doped samples?
The second question pertains to the second band gap at lower energies. Multiple peaks exist at lower energies.
Which of these lower energy peaks should be considered as the second band gap? Can different particle dimensions, phonon reactions, or lattice disturbances be attributed to the multiplicity of these lower energy peaks? Is it possible not to precisely determine which of these peaks corresponds to the second band gap?
The third question is whether, in the DITM model, one should also expect a decreasing or increasing trend in the band gap, similar to the Tauc model. Or, due to calculating more factors compared to the Tauc model, anticipations of such increasing or decreasing trends might not be straightforward?
Best regards,
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