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

Abstract

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...

InAs/InP nanowires grown by catalyst assisted molecular beam epitaxy on silicon substrates

“…All peaks exhibit the same linear dependence on the excitation power without any clear blue shift indicating a type I band alignment. This is in contrast with earlier reports done by another group where optical investigations suggested a type II alignment [13,14]. Moreover, this study indicates the absence of the state filling effect's signature allowing the attribution of the higher energy side peaks to the excited state emission.…”

“…In particular, monolithic integration of emitters on silicon is still in great demand. While several studies have already been reported on the growth andz optical properties of InP/InAs/InP core-shell NWs on InP substrates [12][13][14], the study of the growth of such heterostructured NWs on Si substrates has not yet been reported. In this context, we have studied the growth of InP/InAs/InP NWs grown on Si substrates by VLS-assisted solid source MBE (ssMBE).…”

Polarized photoluminescence from single wurtzite InP/InAs/InP core-multishell nanowires

“…Polarized photoluminescence from single wurtzite InP/InAs/InP core-multishell nanowires Yasuaki Masumoto,1,a͒ The photoluminescence from single InP/InAs/InP core-multishell nanowires ͑CMNs͒ was highly linearly polarized in perpendicular to the nanowire long axis. Taking account of dielectric confinement of light field, we found the internal optical dipole squared perpendicular to the nanotube long axis d 0x 2 is larger than that parallel to the axis d 0z 2 by two orders of magnitude.…”

“…Nanotubes work as quantum wells and quantum wires and emit bright photoluminescence ͑PL͒ in the near infrared region. 1 Another unique feature of InP/InAs/InP CMNs is the wurtzite structure instead of zincblende structure for both InAs and InP bulk crystals. 2,3 The crystal field as well as spin-orbit interaction in the wurtzite structure split the top valence band into ⌫ 9 ͑A͒-state, ⌫ 7 ͑B͒-state, and ⌫ 7 ͑C͒-state.…”

Population dynamics and dephasing of excitons and electron-hole pairs in polytype wurtzite/zinc-blende InP nanowires

“…Due to the small radial dimensions of the NWs the design of NW heterostructures is not limited by strain as in conventional planar molecular beam epitaxy (MBE) or metal-organic-vapor-phase-epitaxy (MOVPE) thus enabling the fabrication of a wide variety of radial heterostructures as e.g. GaAs/AlGaAs 7 , GaAs/GaP 12 and InP/InAs 13 core-shell NWs. Also axial NW heterostructures 7,14 become feasible that comprise segments of different semiconductor material with nanometer thickness along the NW [15][16][17] .…”