| 1. |
- Håkanson, Ulf, et al.
(författare)
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Photon mapping of single quantum dots by scanning tunneling microscopy induced luminescence spectroscopy
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- Scanning tunneling microscopy induced luminescence (STML) has been used to investigate individual self-assembled InP quantum dots overgrown with GaInP. We will present results correlating the surface morphology with the optical properties of single dots. In particular, the strain induced energy-shift of the dot emission with increasing cap layer thickness and its relation to the overgrowth will be discussed. Effects of the dots on the properties of the overgrown GaInP will also be treated. STML spectra and monochromatic photon maps are compared with results from photoluminescence and transmission electron microscopy measurements. Furthermore, a comparison with theoretical calculations is made
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| 2. |
- Håkanson, Ulf, et al.
(författare)
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Single InP/GaInP quantum dots studied by scanning tunneling microscopy and scanning tunneling microscopy induced luminescence
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:3, s. 494-496
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the optical and structural properties of single, self-assembled InP quantum dots (QDs) overgrown with nominally 5 nm of GaInP, using an ultrahigh-vacuum scanning tunneling microscope (STM) operating at low temperatures. The STM is combined with an optical detection system, which allows us to detect the emission from individual quantum dots with high spatial resolution. We find that the InP QDs act as nucleation points for the GaInP overgrowth, where the strain induced by the overlayer give rise to a QD emission around 1.46 eV. (C) 2002 American Institute of Physics.
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| 3. |
- Johansson, Mikael, et al.
(författare)
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Correlation between overgrowth morphology and optical properties of single self-assembled InP quantum dots
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:12
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the early stages of GaInP overgrowth on InP quantum dots (QD's) experimentally and theoretically. A direct correlation between the surface morphology and the optical properties of individual InP QD's is made using scanning tunneling microscopy (STM) and scanning tunneling luminescence. The geometric structure of the islands is further investigated using cross-sectional transmission electron microscopy (TEM). The overgrowth occurs in three stages; initially the InP QD's act as seeding points for the overgrowth, where the GaInP grows laterally from the side facets of the QD. The growth occurs preferentially in the [110] direction and elongated GaInP/InP islands are formed. As the overgrowth continues the islands increase laterally in size and GaInP also starts to grow between the islands, but not covering the top of the InP QD's. The growth of GaInP on top of the QD's commences once the islands have begun to coalesce. Using a model based on the STM and TEM results the electronic structures of the QD's have been calculated by eight-band k.p theory. The calculations are in good agreement with the experimental results. Our findings unravel the details of the strain induced energy shift of the QD luminescence previously reported [Pistol , Appl. Phys. Lett. 67, 1438 (1995)].
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| 4. |
- Metaferia, Wondwosen, et al.
(författare)
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GaAsP Nanowires Grown by Aerotaxy
- 2016
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:9, s. 5701-5707
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Tidskriftsartikel (refereegranskat)abstract
- We have grown GaAsP nanowires with high optical and structural quality by Aerotaxy, a new continuous gas phase mass production process to grow III-V semiconductor based nanowires. By varying the PH3/AsH3 ratio and growth temperature, size selected GaAs1-xPx nanowires (80 nm diameter) with pure zinc-blende structure and with direct band gap energies ranging from 1.42 to 1.90 eV (at 300 K), (i.e., 0 ≤ x ≤ 0.43) were grown, which is the energy range needed for creating tandem III-V solar cells on silicon. The phosphorus content in the NWs is shown to be controlled by both growth temperature and input gas phase ratio. The distribution of P in the wires is uniform over the length of the wires and among the wires. This proves the feasibility of growing GaAsP nanowires by Aerotaxy and results indicate that it is a generic process that can be applied to the growth of other III-V semiconductor based ternary nanowires.
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| 5. |
- Panev, Nikolay, et al.
(författare)
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Spectroscopic studies of random telegraph noise in small InP quantum dots in GaxIn1-xP
- 2004
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 70:7
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Tidskriftsartikel (refereegranskat)abstract
- We have observed and investigated random telegraph noise in the photoluminescence (PL) from small InP quantum dots (QDs) in GaInP. Very few of the QDs exhibit switching between two states, which have similar total intensities, but distinctly different spectra. Usually, one of the states dominates at low excitation power and the other at high excitation power. The switching occurs on the time scale of one second and is stable with respect to annealing at room temperature, but the QDs can be permanently settled in one of the states by strong illumination. Measurements on QDs in a semitransparent Schottky diode show that the QDs can be reversibly forced into one of the states by applying a reverse bias of the order of 1 V. This switching behavior is different than what has been previously observed because there is no change in the total PL intensity and, at the same time, both states cannot be explained as simply being shifted by an electric field, but show distinctly different emission spectra.
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| 6. |
- Persson, Jonas, et al.
(författare)
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Charging control of InP/GaInP quantum dots by heterostructure design
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85:21, s. 5043-5045
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor quantum dots are often charged due to accumulation from a doped host material. Using low-temperature photoluminescence, we have studied the charging of single self-assembled InP dots in structures designed to control the electron population in a weakly n-type environment. By using designed heterostructures to position the Fermi level of the structure, not requiring electric fields or currents, we show that the electron accumulation can be reduced from approximately 18 electrons in the dot to approximately 8 electrons. In particular, we show that the single quantum dot luminescence spectrum of the Fermi-level pinned structure perfectly matches the low-energy part of the highly charged reference spectrum, a phenomenon predicted by the model for multiple charging of quantum dots. (C) 2004 American Institute of Physics.
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| 7. |
- Persson, Jonas, et al.
(författare)
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Electron accumulation in small and larger semiconductor quantum dots
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- We present μ-PL and k·p calculations of self-assembled InP quantum dots (QDs) in GaInP. The QDs come in two subsets; the larger are pyramid shaped, and about 15 nm high with a base of about 40 by 50 nm, and the smaller have similar lateral extension but with a considerably lesser height. The change in size is accompanied by a change in quantum confinement and thus a change in emission energy. Moreover, there is a transition from a single sharp emission peak for the smallest dots to several 1 meV broad lines over a 50 meV range for the largest dots due to unintentional doping in the barrier material. The result is an electron accumulation in the QDs, and emission in an energy range corresponding to the energy range occupied by these electrons. Larger QDs accumulate more electrons and thus emit over a larger energy range. For the smaller dots we show that the precise position of the electronic ground state with respect to the Fermi level determines whether the dot is neutral or charged
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| 8. |
- Persson, Jonas, et al.
(författare)
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Optical and theoretical investigations of small InP quantum dots in GaxIn1-xP
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 67:3
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Tidskriftsartikel (refereegranskat)abstract
- We have studied small InP quantum dots in a GaInP matrix theoretically and experimentally. Using low-temperature photoluminescence spectroscopy in conjunction with six band k.p calculations, including direct and exchange interactions, we show that the dot size is a crucial parameter that determines whether the dot is neutral or charged with electrons in the nominally undoped n-type host material. For a small enough quantum dot, the conduction-band ground state is positioned above the Fermi level and the dot remains neutral. However, as soon as the dot is large enough for the conduction-band ground state to be located below the Fermi level the dot is charged. Furthermore, we show that, for neutral quantum dots, the position of the bi-exciton emission line with respect to the exciton emission line depends on the size of the quantum dot and that the bi-exciton emission can be on either side of the exciton emission: for the smallest dots the bi-exciton emission is always at higher energy than the exciton emission but for larger dots the ordering is the opposite with the exciton emission line on the high-energy side.
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| 9. |
- Persson, Jonas, et al.
(författare)
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Strain effects on individual quantum dots: Dependence of cap layer thickness
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:8
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the effects of strain on individual self-assembled quantum dots (QDs) exemplified by InP dots embedded in GaInP. The quantum dot sample was etched from the top and in this way the amount of capping material was reduced. In a sequence of etch cycles, the cap layer was thinned, and the photoluminescence from several individual QDs could be followed as a function of cap layer thickness. The evolution of the emission spectra clearly depended on the quantum dot size. We interpret this as arising from differences in the aspect ratio for quantum dots of different sizes. The influence of the capping layer, for different QD geometries, was modeled using deformation potential theory with the strain calculated using a full three-dimensional linear elasticity model. The results agree well with the experimental observations.
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