I have doped Cr, Mn, Co, Ni and Cu in bilayer MoS2 but the band gap reduces after Cr and Mn doping, and other three elements (Co, Ni and Cu) convert the semiconductor into metal. can anybody tell me its reason?
Band gap of TMDCs or layered systems are very sensitive to doping. This system is known as laboratory for understanding many-body interactions. With increase in doping trion feature starts emerging changing the carrier dynamics and thus leading to change in the band gap. If your TM are creating p doping in your system then your PL peak should shift to red and if n doping is getting created then it will shift the peak to blue or it can get quenched too. Along with the doping there can be strain MoS2 layer account to the change in PL peak position or band gap energy.
Dear Anam,
independent on that what Geeta wrote, I have an additional proposal to understand your results.
The properties of solids strongly depend on the doping concentration:
If the concentration is high enough (comparable to the density of states), you observe the formation of impurity bands. The impurity level broadens and merges with the band (of conductivity or valence band). Therefore the gap seems to be reduced. Absorbtion measurements show a red shift.
At higher doping concentrations the fermi level shifts into the band of conductivity (or valence band) and a metal like state is formed. This is called a degenerated semiconductor. Contrary to a normal metal the properties of a degenerated semiconductor have not intrinsic but extrinsic cause.
With Regard
R. Mitdank
Hi Anam,
Doping of metal ions into metal oxides/sulfides matrix is also called as cation doping. Whereas doping of non-metallic ions is called anion doping.
When we carry out cation doping, downward shift of conduction band takes place giving rise to reduced band gap energy.
Similarly, when we dope with anions such as N, S, upward shift of valance band takes place again giving raise to reduced band gap energy.
For more info, you can refer this paper:
Article Recent advances in non-metals-doped TiO2 nanostructured phot...
Hope it helps!
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