Reordering orbitals of semiconductor multi-shell quantum dot-quantum well heteronanocrystals

Şahin, Mehmet; Nizamoğlu, Sedat; Yerli, Ozan; Demir, Hilmi Volkan

doi:10.1063/1.3678585

“…Schrodinger equation of an exciton is given as follows 30 :Here, the first and second terms are the carrier charge kinetic energies of the electron and hole, respectively. The subsequent term is the attractive Coulombic interaction energy between the electron and hole, ħ is the reduced Planck constant, and are the position dependent electron and hole effective masses, respectively.…”

Section: The Model and Theorymentioning

confidence: 99%

“…In the said structure, the electron moves in a mean potential induced by the hole and similarly, the hole moves in a mean potential induced by the electron 32 . In HF (Hartree-Fock) calculations, the carriers Schrodinger equations can be simplified as 30 :In these equations, q e and q h are the charges, and R e (r) and R h (r) represents the radial wavefunctions of the electron and hole, respectively. φ e (φ h ) is the Coulombic potential generated by the electron (hole).…”

Section: The Model and Theorymentioning

confidence: 99%

“…The electrostatic potentials induced by the electron and hole can be solved by the Poisson equations, as given below 30 :here, ρ e (r) and ρ h (r) are the linear carrier charge densities, and κ(r) is the position dependent bulk dielectric constant of the core and shell of the QD. Equations 9 and 10 models the electronic potential images which arise due to surface polarization at the core-shell boundaries.…”

Section: The Model and Theorymentioning

confidence: 99%

See 1 more Smart Citation

Wavefunction Engineering of Type-I/Type-II Excitons of CdSe/CdS Core-Shell Quantum Dots

Nandan

¹

,

Mehata

²

2019

Sci Rep

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Nanostructured semiconductors have the unique shape/size-dependent band gap tunability, which has various applications. The quantum confinement effect allows controlling the spatial distribution of the charge carriers in the core-shell quantum dots (QDs). Upon increasing shell thickness (e.g., from 0.25–3.25 nm) of core-shell QDs, the radial distribution function (RDF) of hole shifts towards the shell suggesting the confinement region switched from Type-I to Type-II excitons. As a result, there is a jump in the transition energy towards the higher side (blue shift). However, an intermediate state appeared as pseudo Type II excitons, in which holes are co-localized in the shell as well core whereas electrons are confined in core only, resulting in a dual absorption band (excitation energy), carried out by the analysis of the overlap percentage using the Hartree-Fock method. The findings are a close approximation to the experimental evidences. Thus, the understanding of the motion of e-h in core-shell QDs is essential for photovoltaic, LEDs, etc.

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“…23,52 Wave function engineering approach for band alignment and wave function overlap. With the internal structure of the CSQDs determined as CdxZn1-xTe/CdSe using EXAFS, TEM, and elemental analysis, we then applied a simple wave function engineering approach 55 (see SI section 13 for details) to determine the band alignment regime and electron-hole wave function overlap for the lowest-energy 1Shh and 1Se states. In this method, an effective mass approximation was made in order to simplify the atomic-scale variation of potentials.…”

Section: Particle Models and Control Experimentsmentioning

confidence: 99%

Internal Atomic-Scale Structure Determination and Band Alignment of II-VI Quantum Dot Heterostructures

Gentle

¹

,

Wang²,

Haddock³

et al. 2019

Preprint

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This work shows that ZnTe/CdSe core/shell quantum dots synthesized by standard literature procedures in actuality have an alloyed CdxZn1-xTe core. We employ X-ray absorption spectroscopy (XAS) at all four K-shell ionization edges (Zn, Te, Cd, Se) and perform a global fitting analysis in order to extract the first-shell bond distances. We combine our XAS results with transmission electron microscopy (TEM) sizing and elemental analyses, which allows us to propose models of the internal particle structure. Our multimodal characterization approach confirms (1) the presence of Cd-Te bonds, (2) cation alloying in the particle core (and the absence of anion alloying), and (3) a patchy pure-phase CdSe shell. We synthesize particles of different shell thicknesses and performed synthetic control studies that allowed us to discard a ZnTe/CdTe/CdSe core/shell/shell structure and confirm the alloyed core/shell structure. Our structural analysis is extended with electronic band structure calculations and UV/vis absorption spectroscopy, demonstrating that the alloyed CdxZn1-xTe/CdSe core/shell quantum dots exhibit a direct band gap, different from the predicted type-II band alignment of the intended ZnTe/CdSe core/shell quantum dots. This study highlights the challenges with synthesizing II-VI quantum dot heterostructures and the power of XAS for understanding the internal structure of heterogenous nanoparticles.

show abstract

“…23,52 Wave function engineering approach for band alignment and wave function overlap. With the internal structure of the CSQDs determined as CdxZn1-xTe/CdSe using EXAFS, TEM, and elemental analysis, we then applied a simple wave function engineering approach 55 (see SI section…”

Section: Bond ∆R (å)mentioning

confidence: 99%

Internal Atomic-Scale Structure Determination and Band Alignment of II-VI Quantum Dot Heterostructures

Gentle¹,

Wang²,

Haddock³

et al. 2019

Preprint

0

View full text Add to dashboard Cite

This work shows that ZnTe/CdSe core/shell quantum dots synthesized by standard literature procedures in actuality have an alloyed CdxZn1-xTe core. We employ X-ray absorption spectroscopy (XAS) at all four K-shell ionization edges (Zn, Te, Cd, Se) and perform a global fitting analysis in order to extract the first-shell bond distances. We combine our XAS results with transmission electron microscopy (TEM) sizing and elemental analyses, which allows us to propose models of the internal particle structure. Our multimodal characterization approach confirms (1) the presence of Cd-Te bonds, (2) cation alloying in the particle core (and the absence of anion alloying), and (3) a patchy pure-phase CdSe shell. We synthesize particles of different shell thicknesses and performed synthetic control studies that allowed us to discard a ZnTe/CdTe/CdSe core/shell/shell structure and confirm the alloyed core/shell structure. Our structural analysis is extended with electronic band structure calculations and UV/vis absorption spectroscopy, demonstrating that the alloyed CdxZn1-xTe/CdSe core/shell quantum dots exhibit a direct band gap, different from the predicted type-II band alignment of the intended ZnTe/CdSe core/shell quantum dots. This study highlights the challenges with synthesizing II-VI quantum dot heterostructures and the power of XAS for understanding the internal structure of heterogenous nanoparticles.

show abstract

Reordering orbitals of semiconductor multi-shell quantum dot-quantum well heteronanocrystals

Cited by 28 publications

References 26 publications

Wavefunction Engineering of Type-I/Type-II Excitons of CdSe/CdS Core-Shell Quantum Dots

Wavefunction Engineering of Type-I/Type-II Excitons of CdSe/CdS Core-Shell Quantum Dots

Internal Atomic-Scale Structure Determination and Band Alignment of II-VI Quantum Dot Heterostructures

Internal Atomic-Scale Structure Determination and Band Alignment of II-VI Quantum Dot Heterostructures

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