Abstract
In order to discern the formation of epitaxial growth of CdS shell over CdTe nanocrystals, kinetics related to the initial stages of the growth of CdS on CdTe is investigated using ab-initio methods. We report diffusion of sulfur adatom on the CdTe (111) A-type (Cd-terminated) and B-type (Te-terminated) surfaces within the density functional theory (DFT). The barriers are computed by applying the climbing Nudge Elastic Band (c-NEB) method. From the results surface hopping emerges as the major mode of diffusion. In addition, there is a distinct contribution from kick-out type diffusion in which a CdTe surface atom is kicked out from its position and is replaced by the diffusing sulfur atom. Also, surface vacancy substitution contributes to the concomitant dynamics. There are sites on the B- type surface that are competitively close in terms of the binding energy to the lowest energy site of epitaxy on the surface. The kick-out process is more likely for B-type surface where a Te atom of the surface is displaced by a sulfur adatom. Further, on the B-type surface, subsurface migration of sulfur is indicated. Furthermore, the binding energies of S on CdTe reveal that on the A-type surface, epitaxial sites provide relatively higher binding energies and barriers than on B-type.
Highlights
Semiconducting core/shell nano structures have attracted much attention over last decade due to their possible device and sensor related applications.[1,2,3,4] Most of the work pertinent to the photonics applications considers mainly CdSe core
In order to discern the formation of epitaxial growth of CdS shell over CdTe nanocrystals, kinetics related to the initial stages of the growth of CdS on CdTe is investigated using ab-initio methods
Lane et al have found out the quality of CdTe/CdS interface is strongly depended on the type of Sulfur source used for the diffusion and have observed two diffusion mechanisms for Sulfur which can be characterized by activation energies 1.06 and 1.7 eV and a more rapid diffusion mechanism aCorresponding author
Summary
Semiconducting core/shell nano structures have attracted much attention over last decade due to their possible device and sensor related applications.[1,2,3,4] Most of the work pertinent to the photonics applications considers mainly CdSe core. CdS) onto a soft nanocrystalline core (CdTe) to form a lattice-mismatched quantum dot can considerably change the conduction and valence band energies of both the core and the shell.[8] In the field of solar cells the conversion efficiency of CdTe/CdS junction is commonly considered to be influenced by inter-diffusion at the interface of CdTe-CdS.[9,10] The diffusion of Sulfur (Te) on CdTe (CdS) will form a solid layer at the n-CdS/p-CdTe interface which is an intensely compensated resistant layer.[11] S. Lane et al have found out the quality of CdTe/CdS interface is strongly depended on the type of Sulfur source used for the diffusion and have observed two (unknown) diffusion mechanisms for Sulfur which can be characterized by activation energies 1.06 and 1.7 eV and a more rapid diffusion mechanism
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