Abstract
CdTe/CdSe heterostructure multilayer thin films and single layers of CdSe and CdTe thin films were prepared. Sequential thermal evaporation technique is made possible to adjust the layer thickness precisely. XRD studies were used to calculate average size of the crystallites and confirmed the (111) and (100) planes of CdTe and CdSe, respectively. Bulk CdTe has band gap energy of 1.54 eV that can be shifted to larger values by reducing the crystallite size to dimensions smaller than the Bohr radius of the exciton. Experimentally measured energy levels show the spin–orbit split of valance band of CdTe. Crystallite sizes (7–12 nm) were calculated with the predictions of effective mass approximation model (i.e., Brus model) which shows that the diameter of crystallites were much smaller than the Bohr exciton diameter (14 nm) of CdTe. It is found that the emission peaks of the prepared CdTe/CdSe ML samples were shifted from the peaks of CdSe and CdTe single layers toward red region as a characteristic of type II band alignment.
Highlights
Quantum size effects in semiconductors occur when the size of the particle is small in comparison with Bohr excitonic radius which acts as a natural length scale of the electron–hole pair
We report the formation of type II nanocrystals in CdTe/ CdSe multilayer thin films prepared by physical vapor deposition method where thickness of each layer can be controlled accurately up to few nanometers
It has been generally proved that the quantum confinement effect should be observable if the radius of nano crystallites becomes less than the Bohr excitonic radius for corresponding material
Summary
Quantum size effects in semiconductors occur when the size of the particle is small in comparison with Bohr excitonic radius which acts as a natural length scale of the electron–hole pair. This effect is a direct consequence of. We report the formation of type II nanocrystals in CdTe/ CdSe multilayer thin films prepared by physical vapor deposition method where thickness of each layer can be controlled accurately up to few nanometers. Alternating coating of CdTe and CdSe heterostructure semiconductors under high vacuum condition provides an uniform sequential arrangement of layers in the order of few nanometers so that trapping of electron–hole pair is made possible in simple steps. Order of Thickness Total no of the number of sublayers sample layers in the sample
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