Excited-state spectroscopy of InP quantum dots

Bertram, D.; Mićić, O. I.; Nozik, Arthur J.

doi:10.1103/physrevb.57.r4265

Cited by 49 publications

(47 citation statements)

References 22 publications

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“…28,29 For InP, InAs, and CdSe, it was found that the bulk spacing between the Γ 1c level and the next lowest level in the conduction band is sufficiently large (see Table I) that the effects of quantum confinement do not cause the dots to develop an indirect band gap, even for dots as small as 20Å radius. There are several recent experiments 11,[22][23][24][25][26][27][28]30 which clearly show the existence of a direct band gap in free standing InP, 31 InAs, 12 and CdSe 11 quantum dots. These experiments observe a strong fundamental photoluminescence (PL) peak that blue shifts as the size of the dots decreases which is interpreted as evidence for a direct band gap in these dots.…”

Section: Direct Gap Dots: Inp Inas and Cdsementioning

confidence: 98%

Indirect band gaps in quantum dots made from direct-gap bulk materials

Williamson

Franceschetti

et al. 1999

Journal of Elec Materi

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The conditions under which the band gaps of free standing and embedded semiconductor quantum dots are direct or indirect are discussed. Semiconductor quantum dots are classified into three categories; (i) free standing dots, (ii) dots embedded in a direct gap matrix, and (iii) dots embedded in an indirect gap matrix. For each category, qualitative predictions are first discussed, followed by the results of both recent experiments and state of the art pseudopotential calculations. We show that: • Free standing dots of InP, InAs, and CdSe will remain direct for all sizes, while dots made of GaAs and InSb will turn indirect below a critical size. • Dots embedded within a direct gap matrix material will either stay direct (InAs/GaAs at zero pressure) or will become indirect at a critical size (InSb/ InP). • Dots embedded within an indirect gap matrix material will exhibit a transition to indirect gap for sufficiently small dots (GaAs/AlAs and InP/ GaP quantum well) or will be always indirect (InP/GaP dots, InAs/GaAs above 43 kbar pressure and GeSi/Si dots). In indirect nanostructures, charge separation can occur with electrons and holes localized on different materials (flat InP/GaP quantum well) or with electrons and holes localized in different layers of the same material (concentric cylindrical GaAs/AlAs layers).

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Section: Direct Gap Dots: Inp Inas and Cdsementioning

confidence: 98%

Indirect band gaps in quantum dots made from direct-gap bulk materials

Williamson

Franceschetti

et al. 1999

Journal of Elec Materi

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“…Colloidal NCs capped with a TOP-TOPO organic ligand (named hereafter, InP/TOP-TOPO) were further etched with HF (etched InP/TOP-TOPO) (98,99), or covered by ZnS epitaxial shells (InP/ZnS, InP/ZnCdSe 2 ) (99). The impact of the quantum-size effect in colloidal NCs is of special interest owing to their large exciton Bohr radius (11.3 nm) and relatively narrow band gap (1.34 eV) (32,38,99,100). Although carrier confinement in colloidal NCs is expected to lead to enhanced PL efficiency, this is frequently unobserved, presumably owing to the trapping of carriers at the surface.…”

Section: Odmr Of Nonetched and Hf Etched Inp/top-topo Etched Inp/topmentioning

confidence: 99%

Optically Detected Magnetic Resonance Studies of Colloidal Semiconductor Nanocrystals

Lifshitz

Fradkin

Glozman

et al. 2004

Annu. Rev. Phys. Chem.

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The review describes the studies of the magneto-optical properties of II-VI and III-V semiconductor nanocrystals (NCs) capped with organic or inorganic epitaxial shells. The investigations focused on the chemical identification of localization sites (core, shell, or interface) of photogenerated carriers in spherical NCs and elucidated the influence of the surface/interface quality on the optical properties of the materials. Optically detected magnetic resonance (ODMR) spectroscopy was used for the study of the proposed physical properties. The ODMR method provides the means to identify the surface/interface sites and correlate them with specific optical transition. In addition, this method reveals information about the spin multiplicity of band edge and trapped states and the electron-hole exchange interaction, determines the spectroscopic g-factors, distinguishes between the radiative and nonradiative characteristic of a trapping site, and evaluates the spin-lattice relaxation times.

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“…Complexities in the valence band levels of the nanocrystal result from the quantum-con®nement-enhanced mixing of close-lying bulk semiconductor bands 21,22 . The mixing relaxes some of the optical transition selection rules, leading to rich and complex optical spectra of the nanocrystals 5,9,23 . The above correlation is also important when examining possible effects of charging and tip-induced electric ®eld in the tunnelling measurements on the nanocrystal level structure.…”

mentioning

confidence: 99%

Identification of atomic-like electronic states in indium arsenide nanocrystal quantum dots

Banin¹,

Cao²,

Katz³

et al. 1999

Nature

572

519

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Semiconductor quantum dots, due to their small size, mark the transition between molecular and solid-state regimes, and are often described as`arti®cial atoms' (refs 1±3). This analogy originates from the early work on quantum con®nement effects in semiconductor nanocrystals, where the electronic wavefunctions are predicted 4 to exhibit atomic-like symmetries, for example`s' and`p'. Spectroscopic studies of quantum dots have demonstrated discrete energy level structures and narrow transition linewidths 5±9 , but the symmetry of the discrete states could be inferred only indirectly. Here we use cryogenic scanning tunnelling spectroscopy to identify directly atomic-like electronic states with s and p character in a series of indium arsenide nanocrystals. These states are manifest in tunnelling current±voltage measurements as two-and six-fold single-electron-charging multiplets respectively, and they follow an atom-like Aufbau principle of sequential energy level occupation 10 .InAs nanocrystals for this study were prepared using a solutionphase pyrolytic reaction of organometallic precursors. These nanocrystals are nearly spherical in shape, with size controlled between 10 and 40 A Ê in radius 11 . The nanocrystal surface is passivated by organic ligands which also provide chemical accessibility for quantum dot (QD) manipulation: for example, to prepare``nanocrystal molecules'' 12,13 , nanocrystal-based light-emitting diodes 14 , and to fabricate single-electron tunnelling devices 15 . For the tunnelling spectroscopy studies we link the nanocrystals to a gold ®lm via hexane dithiol molecules 16 . Figure 1a (left inset) shows a scanning tunnelling microscope (STM) topographic image of an isolated InAs QD, 32 A Ê in radius. Also shown in Fig. 1a is a tunnelling current±voltage (I±V) curve that was acquired after positioning the STM tip above the QD and disabling the scanning and feedback controls, realizing a doublebarrier tunnel junction (DBTJ) con®guration 17±19 (Fig. 1a, right inset). A region of suppressed tunnelling current is observed around zero bias, followed by a series of steps at both negative and positive bias. In Fig. 1b we show the tunnelling conductance spectrum (that is, dI/dV versus V), which is proportional to the tunnelling density of states (DOS) 20 . A series of discrete single-electron tunnelling peaks is clearly observed, where the separations are determined by both single-electron charging energy (addition spectrum) and the discrete level spacings (excitation spectrum) of the QD. The I±V characteristics were acquired with the tip retracted from the QD to a distance where the bias voltage is dropped largely across the tip±QD junction. Under these conditions, conduction (valence) band states appear at positive (negative) sample bias, and the excitation peak separations are equal to the real QD level spacings 19 .On the positive-bias side of Fig. 1, two closely spaced peaks are observed immediately after current onset, followed by a larger spacing and a group of six nearly equidistant peaks. We ...

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Excited-state spectroscopy of InP quantum dots

Cited by 49 publications

References 22 publications

Indirect band gaps in quantum dots made from direct-gap bulk materials

Indirect band gaps in quantum dots made from direct-gap bulk materials

Optically Detected Magnetic Resonance Studies of Colloidal Semiconductor Nanocrystals

Identification of atomic-like electronic states in indium arsenide nanocrystal quantum dots

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