the band gap due to doping decreased (e.g., red shifted) to a certain minimum value (i.e., critical size) with decrease in particle size from an estimated bulk value. Further increasing in doping concentration results in decrease in particle size from the critical size (corresponding to band gap minimum) caused the band gap to increase (i.e., blue-shift). A plausible explanation for this change in band gap with respect to the size of the particle is that the bulk defects induce delocalization of molecular orbitals in the conduction band edge (e.g., LUMO) and create shallow/deep traps in electronic
energy, in turn causing the red-shift of the absorption spectra.
When crystalline size decreased below its size at the band gap
minimum, the traps shifted to higher energy, which resulted in
blue shifting of the absorption spectra.
Question is, how an increase in doping concentration shift the defect level to higher energy inside the band gap!
If we increase doping, the number of majority charge carriers (holes on the p-side and electrons on the n-side) will also grow. This would result in an increase in the breadth of the depletion layer, which is dependent on charge carriers.
Thanks to all of you sharing the information Hadi Jabbar Alagealy Behnam Farid
Emile Haye
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