Comparative energy bandgap analysis of zinc and tin based chalcogenide quantum dots (original) (raw)
Related papers
Chalcogenides-based quantum dots: Optical investigation using first-principles calculations
Materials Science in Semiconductor Processing, 2015
The full potential-linearized augmented plane wave (FP-LAPW) method is implemented in WIEN2K code to calculate the indirect energy gap (Γ-X) using density functional theory (DFT). The Engel-Vosko generalized gradient approximation (EV-GGA) and modified Becke Johnson (mBJ) formalisms are used to optimize the corresponding potential for energetic transition and optical properties calculations of lead chalcogenides (PbS 1 À x Te x) alloys as a function of quantum dot diameter and is used to test the validity of our model of quantum dot potential. The refractive index and optical dielectric constant are investigated to explore best applications for solar cells.
Energy Spectrum in Quantum Dots of Lead and Tin Chalcogenides Semiconducting Compounds
Acta Physica Polonica A, 1992
The energy spectrum of a quantum dot made from IV-VI narrow gap semiconductors is studled. The calculations of the energy levels as functions of the dot radius are performed. When the anisotropy of the bare energy spectrum is strong, the energy levels are calculated using Fal'kovskii's adiabatic approximation for multiband systems. When the quantum dot material has an inverted band gap with respect to the host, the low-energy states within the fundamental gap are shown to arise.
Mercury Chalcogenide Quantum Dots: Material Perspective for Device Integration
Chemical Reviews, 2021
Nanocrystals (NCs) are one of the few nanotechnologies to have attained mass market applications with their use as light sources for displays. This success relies on Cd-and In-based wide bandgap materials. NCs are likely to be employed in more applications as they provide a versatile platform for optoelectronics, specifically, infrared optoelectronics. The existing material technologies in this range of wavelengths are generally not cost effective, which limits the spread of technologies beyond a few niche domains, such as defense and astronomy. Among the potential candidates to address the infrared window, mercury chalcogenide (HgX) NCs exhibit the highest potential in terms of performance. In this review, we discuss how material developments have facilitated device enhancements. Because such NCs are primarily used because of their infrared optical features, we first review the strategies for the associated colloidal growth and electronic structure. The review is organized considering three main device-related applications: light emission, electronic transport and infrared photodetection.
Biointerface Research in Applied Chemistry , 2023
Within the framework of the density functional theory (DFT) using the Wien2k package and the method of linear extended plane waves (FP-LAPW), quantum mechanical calculations were implemented to study the structural, electronic, and optical properties of the ZnxCd1-xTe system in the full range of 0≤x≤1 with a step of 0.25. To determine the optimal volume and grid parameters, the calculation of the total energy of semiconductor nanocomposites CdTe, Zn0.25Cd0.75Te, Zn0.5 Cd0.5 Te, Zn0.75Cd0.25Te, and ZnTe, the generalized gradient approximation (GGA) was applied, which is based on relaxation (optimization) of the volume and minimization of energy (finding the energy of the ground state). According to our calculations within the framework of the DFT, with an increase in the Zn concentration, the constant lattice parameters and the size (volume) of these nanocrystals decrease and are in good agreement with the results obtained this work by the method of X-ray structural analysis. The calculated band gaps of these nanocrystals using the modified exchange-correlation potential mBJ tend to increase, which agrees with the experimental data. The results of spin-polarized and spin-orbit calculations of the band structure showed that all these nanocrystals have direct transition points for electrons. After approximation by the least-squares method, empirical formulas were obtained to establish the concentration dependence of changes in the volumes and bandgap of Zn-modified nanocrystals, which will help experimenters obtain particles with certain sizes and bandgap. Such theoretical studies further open the possibility of accurate prediction of the electronic-energy properties of other semiconductor nanosized structur
UV-visible Absorbtion Studies of ZnSe Chalcogenide Quantum Dots
Nonlinear Optics Quantum Optics
ZnSe chalcogenide quantum dots have been synthesized using chemical precipitation technique at variable pH values. In this paper, effect of pH is seen on the size of ZnSe quantum dots. It is observed that, the size of ZnSe nanoparticles vary with the variation in pH of the precursors used and the quantum dot structures are fabricated at pH of 0.5 and 1.5 only. The band gap measurements are done by using absorption coefficient of ZnSe quantum dots and nanoparticles at different pH values which is calculated by plotting absorbance and wavelength. The bandgap is further calculated by plotting (αhν) 1/2 vs. hν. The particle size is calculated from brus equation which also confirms the quantum confinement effects occurring in ZnSe quantum dots. The absorption edge is used for the calculation of particle size in case of ZnSe nanoparticles. These optical studies are very useful from optoelectronic application point of view of ZnSe quantum dots and nanoparticles.
Acta Materialia, 2012
ZnTe quantum dots (QD) have been synthesized in a quick single-step process by mechanically alloying a stoichiometric mixture of elemental Zn and Te powders at room temperature under Ar with 1 h of milling. The detailed microstructure of these powdered QD has been characterized by both Rietveld analysis of X-ray powder diffraction data and high resolution transmission electron microscopy. The results reveal that almost monodispersed spherical QD of $5 nm size were synthesized after 15 h of milling. These QD all belong to the cubic (Zn blende) phase and contain different kinds of stacking faults but with low lattice strain. The UV-vis absorbance spectra of ZnTe QD depict a significant blue shift with decreasing size of QD and the band gap estimated taken from the sharp absorbance peak position is greater than that of the bulk counterpart. The band gap increases with increasing milling time up to 15 h with a continuous decrease in the size of these QD and, therefore, their optical properties can be fine tuned by varying the milling time.
Optical Properties of Zincblende Cadmium Selenide Quantum Dots
The Journal of Physical Chemistry C, 2010
Although wurtzite cadmium selenide quantum dots (wz-CdSe QDs) are one of the best explored colloidal nanomaterials, no detailed investigation of the optical properties of zincblende cadmium selenide quantum dots (zb-CdSe QDs) has been performed until now. Typically, it is assumed that this material shows the same behavior as the wurtzite modification. To investigate this, we present a study on the optical properties of zb-CdSe QDs, yielding the electronic band gap to size relation (sizing curve), the extinction coefficient at short wavelengths, and the oscillator strength of the band gap transition. Comparing these results with literature data on wz-CdSe QDs we observe, despite a deviation of the sizing curve for diameters above 4 nm, a similar extinction coefficient at short wavelengths and a similar oscillator strength.
Atomistic and continuum modeling of a zincblende quantum dot heterostructure
A multiscale approach was adopted for the calculation of confined states in self-assembled semiconductor quantum dots (QDs). While results close to experimental data have been obtained with a combination of atomistic strain and tight-binding (TB) electronic structure description for the confined quantum states in the QD, the TB calculation requires substantial computational resources. To alleviate this problem an integrated approach was adopted to compute the energy states from a continuum 8-band k.p Hamiltonian under the influence of an atomistic strain field. Such multi-scale simulations yield a roughly six-fold faster simulation. Atomic-resolution strain is added to the k.p Hamiltonian through interpolation onto a coarser continuum grid. Sufficient numerical accuracy is obtained by the multi-scale approach. Optical transition wavelengths are within 7$\%$ of the corresponding TB results with a proper splitting of p-type sub-bands. The systematically lower emission wavelengths in k...
Quantum Confinement Effects on Electronic Properties of ZnO Quantum Dots
Advanced Science, Engineering and Medicine, 2014
We present a theoretical investigation on the quantum confinement effects (QC) on the electronic properties of ZnO quantum dots (QDs) embedded in MgO matrix. The latter material acts as a huge barrier for both electrons and holes so that the ZnO QD behaves as a three-dimensional quantum well. As a computational method, the tight-binding with sp 3 minimal basis set is employed to probe the electronic band structure and inspect the number and the confinement energies of the bound states versus QD size (up to 20 Å) and the valence band offset (VBO). Excellent agreement is achieved between the theoretically obtained band-gap energy (E g ) and the available experimental photoluminescence (PL) data, especially when VBO = 1 eV, which correspond to the maximum compromised confinements between holes and electrons. Furthermore, theoretical results show that the QC energy follows a power-law rule, indicating strong confinement, and is the main reason behind the UV emissions in ZnO QDs. The strong QC of excitons would further explain the enhancement of the oscillator strength and recombination rate. The excellent agreements between our results and the available experimental data do corroborate our claims.
The Band Gap Energy Calculated for Cd 1x Zn x S Quantum Dots grown by the Sol gel Method
2016
This work reports on a theoretical investigation of a band gap energy in the case of Cd1-xZnxS quantum dots embedded in an insulating material by the Sol gel method. Calculations have been computed as a function of Zn composition going from CdS to ZnS taking account on the excitonic binding energy. The obtained results showed a good agreement with experimental data. Thus, this study confirms the validity of the adopted model and can be considered as a helpful support for designing a variety of devices.