Three-Dimensional Confinement in the Conduction Band Structure of InP

Menoni, Carmen S.; Miao, L.; Patel, D.; Mićić, O. I.; Nozik, Arthur J.

doi:10.1103/physrevlett.84.4168

Cited by 18 publications

(10 citation statements)

References 17 publications

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“…16 In fact, because of quantum-confinement effects, such transition tends to occur at lower pressure in quantum dots than it does in the corresponding bulk semiconductor. Our pseudopotential calculations suggest that such pressureinduced direct/indirect transition will also be accompanied by the disappearance of the LR component of the e-h ex- change interaction.…”

Section: ͑2͒mentioning

confidence: 98%

Nonmonotonic size dependence of the dark/bright exciton splitting in GaAs nanocrystals

2009

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The dark/bright exciton splitting ⌬ X in semiconductor nanocrystals is usually caused by electron-hole exchange interactions. Since the electron-hole wave-function overlap is enhanced by quantum confinement, it is generally assumed that ⌬ X increases monotonically as the quantum-dot size decreases. Using atomistic pseudopotential calculations, we show that in GaAs nanocrystals ⌬ X scales nonmonotonically with the nanocrystal size. By analyzing the nanocrystal wave functions in terms of contributions from different k points in the bulk Brillouin zone, we identify the origin of such nonmonotonic behavior in a transition of the lowest conductionband wave function from ⌫ like to X like as the nanocrystal radius decreases below 19 Å. The nonmonotonicity arises because the long-range component of the electron-hole exchange interaction all but vanishes when the electron wave function becomes X like. We also show that the direct/indirect transition induced in GaAs nanocrystals by external pressure results in a sudden reduction in ⌬ X .One of the most interesting aspects of the spectroscopy of semiconductor quantum dots is the existence of a sizable energy splitting between the lowest-energy "dark" exciton state and the lowest-energy "bright" exciton state. For example, in the well-studied case of CdSe colloidal nanocrystals ͑NCs͒, dark/bright splittings in the range of 1-20 meV ͑much larger than the dark/bright splitting of bulk CdSe͒ have been observed using fluorescence line narrowing. 1,2 Since optical transitions from the dark exciton state to the ground state are dipole forbidden, whereas transitions from the bright exciton state are dipole allowed, the radiative lifetime, photoluminescence intensity, and exciton Stokes shift of semiconductor quantum dots are largely determined by thermal population of the bright exciton states and, thus, by the magnitude of the dark/bright splitting. Furthermore, the fine structure of the band-edge exciton and, in particular, the dark/bright exciton splitting determine the dynamics of optically injected spins in semiconductor nanocrystals. 3 In most quantum-dot systems the dark/bright exciton splitting is caused by electron-hole ͑e-h͒ exchange interactions. 1,2,4-9 This mechanism was first proposed to explain the temperature dependence of the photoluminescence lifetime of highly porous Si ͑Ref. 4͒ and later adopted to explain the dark/bright exciton splitting of many other quantum-dot systems. 1,2,9 Since e-h interactions are enhanced by quantum confinement, it is natural to assume that the dark/bright splitting ⌬ X increases as the size of the quantum dot decreases. This is indeed the case for direct-gap CdSe colloidal NCs in which the dark/bright splitting was shown to increase monotonically with the NC radius R, from ⌬ X ϳ 2 meV for R =43 Å to ⌬ X ϳ 18 meV for R =12 Å. 1 Similarly, in the case of indirect-gap Si colloidal NCs, ⌬ X increases monotonically from ϳ8 meV in large NCs ͑emis-sion energy ϳ1.45 eV͒ to ϳ17 meV in small NCs ͑emis-sion energy ϳ1.95 eV͒. 5 Single-band effect...

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Section: ͑2͒mentioning

confidence: 98%

Nonmonotonic size dependence of the dark/bright exciton splitting in GaAs nanocrystals

2009

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“…19,20 In order to study the pressure-dependent band gap and optical properties of semiconductor NCs, the compressed NCs consisted of 0D quantum dots (QDs). [21][22][23][24] In recent years, some other shaped NCs, such as core/shell structures, 25 rods, and tetrapods, 26 have also been investigated. However, so far there have been few reports on the pressure-dependent optical behaviors of the 2D crystalline NPLs.…”

Section: Introductionmentioning

confidence: 99%

Pressure-dependent optical behaviors of colloidal CdSe nanoplatelets

et al. 2015

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Two-dimensional (2D) colloidal anisotropic CdSe nanoplatelets (NPLs) have attracted a great deal of attraction within recent years. Their strong thickness-dependent absorption and emission spectra exhibit significant differences from those of other shaped CdSe nanocrystals (NCs) due to a unique atomically flat morphology. Based on their dielectric confinement effect and the large confinement energy, the 2D CdSe NPLs exhibit the best characteristics of optical and electronic properties as compared to the other CdSe nanocrystallite ensembles. Here, we systematically investigate the in situ high-pressure photoluminescence (PL), absorption, and time-resolved PL spectroscopy of CdSe NPLs with different thicknesses. The pressure-dependent optical behaviors of these NPLs exhibit several remarkable differences compared with those of other shaped CdSe NCs such as a higher phase transition pressure, irreversible PL and absorption spectra after the release of pressure, a narrower tunable range of absorption and PL peak energies, and minor changes in the ranges of PL decay time with increasing pressure. These phenomena and results are attributed to their unique geometric shape and distinctive soft ligand bonding on the surface.

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“…Of particular interest are the pressure variations of excitons confined to nanosize dimensions such as in quantum dots. 4,5,6,7,8,9,10,11,12,13,14 Unlike the case of excitons in higher-dimensional systems, where binding and its pressure dependence reflects mostly manyparticle (correlation) effects, in zero-dimensional (0D) systems where the geometric dimensions are smaller than the excitonic radius, binding of neutral and charged excitons results from an interesting interplay between singleparticle and many-particle effects. Here, we use a realistic description of both single-particle and many-body effects in self-assembled In 0.6 Ga 0.4 As/GaAs quantum dots, showing how pressure affects the different components of exciton binding.…”

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confidence: 99%

Pressure effects on neutral and charged excitons in self-assembled (In,Ga)As∕GaAsquantum dots

2005

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By combining an atomistic pseudopotential method with the configuration interaction approach, we predict the pressure dependence of the binding energies of neutral and charged excitons: X 0 (neutral monoexciton), X − and X + (charged trions), and XX 0 (biexciton) in lens-shaped, selfassembled In0.6Ga0.4As/GaAs quantum dots. We predict that (i) with applied pressure the binding energy of X 0 and X + increases and that of X − decreases, whereas the binding energy of XX 0 is nearly pressure independent.(ii) Correlations have a small effect in the binding energy of X 0 , whereas they largely determine the binding energy of X − , X + and XX 0 . (iii) Correlations depend weakly on pressure; thus, the pressure dependence of the binding energies can be understood within the Hartree-Fock approximation and it is controlled by the pressure dependence of the direct Coulomb integrals J. Our results in (i) can thus be explained by noting that holes are more localized than electrons, so the Coulomb energies obeyThe energetics of excitons reflects a balance between single-particle energy levels E (e) and E (h) of electrons (e) and holes (h) in the system, and the many-particle carrier-carrier interactions, resulting from electron-hole Coulomb and exchange interactions.1,2,3 The variation of excitonic energies under pressure naturally reflects the corresponding variations in single-vs many-particle energies. Of particular interest are the pressure variations of excitons confined to nanosize dimensions such as in quantum dots. 4,5,6,7,8,9,10,11,12,13,14 Unlike the case of excitons in higher-dimensional systems, where binding and its pressure dependence reflects mostly manyparticle (correlation) effects, in zero-dimensional (0D) systems where the geometric dimensions are smaller than the excitonic radius, binding of neutral and charged excitons results from an interesting interplay between singleparticle and many-particle effects. Here, we use a realistic description of both single-particle and many-body effects in self-assembled In 0.6 Ga 0.4 As/GaAs quantum dots, showing how pressure affects the different components of exciton binding. We distinguish the neutral monoexciton X 0 (one e, one h), from the neutral biexciton XX 0(two e, two h), positive trion X + (one e, two h) and negative trion X − (two e, one h). While the effect of pressure on X 0 has been measured, 8,9,10,11,12,13 to the best of our knowledge, the optical spectroscopy of X − , X + and XX 0 under pressure has not yet been reported. For these reason, we provide definite predictions of the pressure effects. Each of the q-charged excitons has a spectrum of levels {ν}, of which the lowest is termed the "ground state of χ q " (χ = X, XX). This spectrum is usually expressed by expanding the many-body excitonic states |Ψ (ν) (χ q ) via a set of Slater determinants |Φ(χ q ) . The latter are constructed from single-particle electron and hole states and accommodate as many carriers as are present in χ q . The single-particle states are solutions to the effective Schrödinge...

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Three-Dimensional Confinement in the Conduction Band Structure of InP

Cited by 18 publications

References 17 publications

Nonmonotonic size dependence of the dark/bright exciton splitting in GaAs nanocrystals

Nonmonotonic size dependence of the dark/bright exciton splitting in GaAs nanocrystals

Pressure-dependent optical behaviors of colloidal CdSe nanoplatelets

Pressure effects on neutral and charged excitons in self-assembled (In,Ga)As∕GaAsquantum dots

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