Type-II behavior in wurtzite InP/InAs/InP core-multishell nanowires

Pal, Bipul; Goto, Ken; Ikezawa, Michio; Masumoto, Yasuaki; Mohan, Premila; Motohisa, Junichi; Fukui, Takashi

doi:10.1063/1.2966343

Cited by 39 publications

(39 citation statements)

References 34 publications

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“…Before the saturation of PL intensity, the emission energy is slightly shifted (∼200 µeV). This energy-shift is attributed to the Stark effect due to the internal electric field induced by the dipoles at the wurtzite and zinc-blende heterointerfaces in the InP NW [18].…”

Section: Related Contentmentioning

confidence: 99%

“…From the streak camera image overlapping of NW and substrate emissions (inset of Fig. 2(c)), the remaining PL signals of InP NW were observed before zero delay time (marked by circle), corresponding to type-II recombination [18]. In what follows we focus on the QD emission with recombination lifetime of ∼2 ns obtained by fitting to a single exponential function (red solid curve).…”

Section: Related Contentmentioning

confidence: 99%

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Exciton coherence in clean single InP/InAsP/InP nanowire quantum dots emitting in infra-red measured by Fourier spectroscopy

Sasakura

Kumano

Suemune

et al. 2009

J. Phys.: Conf. Ser.

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Abstract. We report optical properties of InP/InAsP/InP nanowire quantum dots and single-photon Fourier spectroscopy of an exciton in a single InAsP quantum dot embedded in an InP nanowire. The coherent length of the time-averaged emission originating from the single InAsP QD was measured by a Mach-Zehnder interferometer inserted in the photoluminescence path. Effects of fluctuations in surrounding excess charges trapped in the InP nanowire were investigated by excitation power and energy dependencies.

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Section: Related Contentmentioning

confidence: 99%

Section: Related Contentmentioning

confidence: 99%

Exciton coherence in clean single InP/InAsP/InP nanowire quantum dots emitting in infra-red measured by Fourier spectroscopy

Sasakura

Kumano

Suemune

et al. 2009

J. Phys.: Conf. Ser.

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“…1͑b͒ contains bands of type-II excitons consisting of holes in the InAs ultrathin, strained hexagonal tube and electrons in the InP core or the InP outer shell. 13 Large Stokes shift between PL and PL excitation ͑PLE͒ spectra 13 and slow decay of PL with a decay tail lasting up to 300 ns indicate a type-II band lineup, as is shown in Fig. 1͑c͒.…”

mentioning

confidence: 97%

“…Model-solid theory by Van de Walle 12 explains that nearly hydrostatic strain field forms type-II band lineup. 13 Hole wave function confined in the InAs layer and its quantized energy are calculated by solving effective-mass Schrödinger equation on the finite element method with triangular array of 24 888 nodes for 1/6 section of the InAs hexagonal tube surrounded by inner and outer InP layers. The squared amplitude of the calculated hole envelope functions is displayed in Fig.…”

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confidence: 99%

One- and two-dimensional spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires

et al. 2010

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Spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires ͑CMNs͒ and type-I excitons in an InAs/InP single quantum well ͑SQW͒ was studied by means of time-resolved and spectrally resolved photoluminescence. InP/InAs/InP CMNs in hexagonal symmetry are made of six facets and six edges which work as two-dimensional quantum wells and one-dimensional quantum wires, respectively. At 5 K type-II excitons lose their energy in two stages. In the first stage, two-dimensional spectral diffusion takes place in the type-II quantum well region in CMNs similar to spectral diffusion of type-I excitons in the InAs/InP SQW. In the second stage, slower one-dimensional spectral diffusion takes place in the quantum wire region in CMNs. Acoustic-phonon-mediated migration of excitons to lower-energy-localized states leads to the spectral diffusion in two dimensions and one dimension. Carrier localization in the disordered system depends highly on dimensionality and size. A sharp mobility edge is present for transport in three dimensions while is absent in two dimensions.1 Optical spectroscopy has revealed inhomogeneous broadening of excitons, exciton localization, exciton mobility edge, and exciton spectral diffusion in the disordered system. In fact, spectral diffusion of excitons is widely observed in inhomogeneously broadened exciton bands of quasi-two-dimensional quantum wells ͑QWs͒ ͑Refs. 2-4͒ and three-dimensional mixed crystals. 5,6 Exciton localization, delocalization, and mobility edge are reported in quasitwo-dimensional QW.7 Usually observed features are ͑1͒ photoluminescence ͑PL͒ decay becomes gradually slower with decrease in the photon energy and ͑2͒ time-resolved PL spectrum is gradually shifted toward lower energy as time proceeds. Spectral diffusion is believed to take place by the acoustic-phonon-mediated spatial transfer of excitons localized in the fluctuated potential.It is expected that spectral diffusion highly depends on the dimensionality. In three dimensions, spatial transfer of excitons localized in the fluctuated potential is not difficult, because localized excitons can find the nearby sites with very small energy mismatch. On the other hand, in one dimension, it is difficult because of the limited path for the spatial transfer. Dimensionality-dependent spectral diffusion is predicted theoretically 8 but has not been studied experimentally. Quantum structures having both two-dimensional QWs and onedimensional quantum wires ͑QWRs͒ are idealistic system for the study of the dimensionality-dependent spectral diffusion. In this work, we study type-II exciton dynamics in wurtzite InP/InAs/InP core-multishell nanowires ͑CMNs͒ composed of two-dimensional QWs and one-dimensional QWRs and type-I exciton dynamics in an InAs/InP single QW ͑SQW͒ by using time-resolved and spectrally resolved PL. It is also needed to understand the similarity or difference in the spectral diffusion of type-I excitons and type-II excitons. The scope of the study is to observe two-dimensional and onedimensional spe...

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“…1,[6][7][8][9][10]13,14 However, the energetic barriers in these nanostructures are usually lower than those attainable in colloidal QDs and heteroNCs, which are typically much smaller than their MBE counterparts. Moreover, colloidal chemistry methods are cheaper and easier to upscale than MBE techniques, and offer the additional advantages of processability and easier control over size, shape, and surface.…”

Section: Introductionmentioning

confidence: 99%

Formation of nanoscale spatially indirect excitons: Evolution of the type-II optical character of CdTe/CdSe heteronanocrystals

Donegá

2010

Phys. Rev. B

107

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In this work, the evolution of the optical properties of nanoscale spatially indirect excitons as a function of the size, shape, and composition of the heteronanostructure is investigated, using colloidal CdTe/CdSe heteronanocrystals ͑2.6 nm diameter CdTe core and increasing CdSe volume fraction͒ as a model system. Emphasis is given to quantitative aspects such as the absorption cross section of the lowest-energy exciton transition ͑ SS ͒, Stokes shift, linewidths, and the exciton radiative lifetime. The hole wave function remains confined to the CdTe core while the electron wave function is initially delocalized over the whole heteronanocrystal ͑type-I 1/2 regime͒, and gradually localizes in the CdSe segment as the growth proceeds, until the spatially indirect exciton transition becomes the lowest-energy transition ͑type-II regime͒. This results in a progressive shift of the optical transitions to lower energies, accompanied by a decrease in the oscillator strengths at emission energies and an increase in the exciton radiative lifetimes. The onset of the type-II regime is characterized by the loss of structure of the lowest-energy absorption band, accompanied by a simultaneous increase in the Stokes shift values and transition linewidths. This can be understood by considering the dispersion of the hole and electron states in k space. The SS values decrease rapidly in the type-I 1/2 regime but only slightly in the type-II regime. This shows that the indirect exciton formation leads primarily to redistribution of the oscillator strength of the lowest-energy transition over a wider frequency range. The total absorption cross section per ion-pair unit ͑i.e., integrated over all the exciton transitions͒ remains essentially constant during the heteronanocrystal growth, demonstrating that SS is redistributed from higher-energy transitions of both the CdTe and the CdSe segments, in response to the reduction in the electron-hole wavefunction overlap. Two radiative decay rates are observed and ascribed to exciton states with different degrees of localization of the electron wave function ͑an upper state with a faster decay rate and a lower state with a slower decay rate͒. The results presented here provide fundamental insights into nanoscale spatially indirect exciton transitions, highlighting the crucial role of a number of parameters ͑viz., electron-hole spatial correlation, exciton dispersion and exciton degeneracy, shape effects, and electronic coupling͒.

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Type-II behavior in wurtzite InP/InAs/InP core-multishell nanowires

Cited by 39 publications

References 34 publications

Exciton coherence in clean single InP/InAsP/InP nanowire quantum dots emitting in infra-red measured by Fourier spectroscopy

Exciton coherence in clean single InP/InAsP/InP nanowire quantum dots emitting in infra-red measured by Fourier spectroscopy

One- and two-dimensional spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires

Formation of nanoscale spatially indirect excitons: Evolution of the type-II optical character of CdTe/CdSe heteronanocrystals

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