Two-dimensional cadmium selenide electronic and optical properties: first principles studies

Abstract

Structural, electronic and optical properties of two-dimensional (2D) cadmium selenide (CdSe) structures with 2 × 2 periodicities are investigated. First principles total energy calculations are performed within the periodic density functional theory. Initially, the structural properties are determined using the local density approximation as implemented in the PWscf code of quantum ESPRESSO package. To investigate the electronic properties, the GW method is applied to determine the energy gap within the plasmon pole and the random phase approximations. Optical properties are investigated to determine the dielectric constant and the Bethe-Salpeter theory is used to calculate the exciton binding energies. Zinc blende and wurtzite phases are considered to calculate the bulk energy gaps, which are compared to the experimental values, finding good agreement. The 2D structure exhibits an energy gap larger than that of the bulk, indicating the effects of reduction in dimensionality; these changes can be attributed to the dangling bonds that are present in the 2D layer.

Copper Doping in II–VI Semiconductor Nanocrystals: Single-Particle Fluorescence Study

“…The obtained length of the Cd−Se bond (2.63 ± 0.01 Å) is similar to that of bulk CdSe (2.61 Å), 27 suggesting that the NC does not undergo structural changes or distortion upon doping with a small percentage (∼1%). However, the Cu-Se bond length is substantially reduced to 2.35 Å, due to the smaller atomic number element like Cu (Z = 29) replacing a higher atomic numbered Cd (Z = 48).…”

Synthesis of Zinc Blende-Phased CdSe Nanocrystals with Size-Tunable Optical Properties and Adjustable Valence Band Positions

“…Thus, such optical features should be general properties of semiconductor materials. Cadmium selenide quantum dots and nanostructures have been widely prepared to tune their absorption and emission band wavelengths for light-emitting and display applications. − CdSe has reported bulk band gaps in the range of 1.68–1.74 eV. , It should be interesting to grow the classic CdSe nanocrystals with sizes far beyond the quantum confinement regime to demonstrate that they also possess continued absorption and emission band shifts, in contrast to the general belief of a practically fixed band gap for particles well beyond 10 nm. The excitonic Bohr radius of CdSe is 5.3 nm .…”

“…16−18 CdSe has reported bulk band gaps in the range of 1.68−1.74 eV. 19,20 It should be interesting to grow the classic CdSe nanocrystals with sizes far beyond the quantum confinement regime to demonstrate that they also possess continued absorption and emission band shifts, in contrast to the general belief of a practically fixed band gap for particles well beyond 10 nm. The excitonic Bohr radius of CdSe is 5.3 nm.…”

Colloidal Mercury-Doped CdSe Nanoplatelets with Dual Fluorescence

“…9−11 Among them, quasi-two-dimensional (2D) NPLs present a very interesting subset of properties, such as the absence of roughness on the top and bottom facets, 11,12 leading to extremely narrow photoluminescence (PL), relatively high absorption cross sections, 13−15 and suppressed Auger-recombination rates, 16 which make them prime candidates for lasing and light-emitting diode applications. 17−19 Due to these unique properties, they have sparked efforts in understanding their electronic structure 20,21 and, especially in the case of the zinc-blende particles, the underlying formation mecha-nism. 22,23 Inherent to the quantum confinement nature of these 2D structures, however, is the discrete character of thickness variations in steps of monolayers (MLs) and, therefore, the absence of continuous tunability.…”

“…Cadmium selenide has served as a model system for wet-chemical synthesis since the pioneering efforts on spherical quantum dots in 1993 . Continuous efforts have since led to the control of the size, crystal structure, − and shape of these NCs, resulting in the availability of a variety of species, such as nanorods, , tetrapods, , and nanoplatelets (NPLs). − Among them, quasi-two-dimensional (2D) NPLs present a very interesting subset of properties, such as the absence of roughness on the top and bottom facets, , leading to extremely narrow photoluminescence (PL), relatively high absorption cross sections, − and suppressed Auger-recombination rates, which make them prime candidates for lasing and light-emitting diode applications. − Due to these unique properties, they have sparked efforts in understanding their electronic structure , and, especially in the case of the zinc-blende particles, the underlying formation mechanism. , Inherent to the quantum confinement nature of these 2D structures, however, is the discrete character of thickness variations in steps of monolayers (MLs) and, therefore, the absence of continuous tunability. Very recent synthetic developments opened up the attainable emission wavelengths of CdSe NPLs to about 625 nm for the eight-ML species , and resulted in the continuous tuning of their optical properties by means of an advanced surface design. , However, a further shift into the low-energy domain of the electromagnetic spectrum requires other synthetic strategies such as alloying, doping, or the preparation of type II heterostructures since pure CdSe is ultimately restricted by its relatively large bulk band gap of >1.7 eV …”