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...
We observed that the biexciton binding energy in InAs quantum rhombic disks (QRDs) is enhanced by twice compared with that for InAs quantum dots (QDs) so far reported around 1.24 μm nearby the telecommunication wavelength. The heterodyne-detected four-wave-mixing detected the exciton-biexciton quantum beat superposed on photon echo decay, giving the biexciton binding energy of 3.4 meV to 3 monolayer (ML) InAs QRDs and 4.1 meV to 4 ML InAs QRDs, respectively. The largest biexciton binding energy of 4.1 meV in InAs QDs is ascribed to increased electron-hole overlap in confined geometry with a minimized strain distribution.
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