Theoretical investigation of energy gap bowing in CdS_xSe_1−x alloy quantum dots

Abstract

To investigate energy gap bowing in homogeneously alloyed CdSSe quantum dots (QDs) and to understand whether it is different from bulk, we perform density functional theory based electronic structure calculations for spherical QDs of different compositions x (0 ≤ x ≤ 1) and of varying sizes (2.2 to 4.6 nm). We find the bowing constant to be slightly higher than in bulk for different sizes of quantum dots. The change in the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of QDs mainly arises due to the change in the LUMO energies. Upon comparison, the highest occupied molecular orbital (HOMO) energies remain almost the same. This observation is in contrast to the results for bulk CdSSe (J. Appl. Phys., 2000, 87, 1304). We identify the change in the lattice constant on alloying as the main factor affecting the hybridization of the anion-cation state, which in turn results in bowing of the HOMO-LUMO gap. To understand the shape dependence of the band gap, we perform electronic structure calculations for pyramid-shaped and cubic QDs of different compositions and of two different sizes. The study of l-decomposed partial charge density and Bader charge analysis is useful to understand the difference in the nature of bonding with changing size and composition. The results presented will assist in experiments and hence can lead to the possible applications of CdSSe QDs.

Tuning optoelectronic response of lateral core-alloyed crown nanoplatelets: type-II CdSe–CdSe1−x Te x

“…It is in accord with the available experimental work [15]. Earlier reports on the bandgap bowing in the alloyed structures have attributed the underlying nonlinearity to a lattice parameter, a change in the anion-cation bond lengths, electronegativity difference of the anions, orbital hybridization and so on [74,75]. Regardless the ML thickness of NPLs alloys, we assume that the bowing origins are similar.…”

“…On the other hand, the parabolic behavior of the crown energies transitions with anionic composition (x) can be considered as signature of the band bowing effect, which has been also observed in alloyed CdS x Se 1−x QDs and bulk CdSe 1−x Te x [74][75][76]. The mechanism of the band bowing effect in CdSe 1−x Te x NPLs alloys will be further discussed later, in this paper, using our DFT calculation.…”

OPTICAL ATTENUATION MODELLING OF PbSexS1-x QUANTUM DOTS WITH VEGARD'S LAW AND BRUS EQUATION USE

“…The electronic properties of PbSe x S 1-x will change as 'x' function varies [0-1] which directly influences many applications on Pb based devices under different conditions. The electronic properties of this alloy was studied by using Vegard's law [19][20][21] and optical properties of the alloy was studied by Brus equation [22]. In this research, an attempt has been made to observe how Brus equation and Vegard's law can be used to analyze attenuation of radiation versus wavelength and energy band gap of this ternary alloy.…”