| 1. |
- Wernersson, Lars-Erik, et al.
(författare)
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Metalorganic vapor phase epitaxy-grown GaP/GaAs/GaP and GaAsP/GaAs/GaAsP n-type resonant tunnelling diodes
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:10, s. 1841-1843
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Tidskriftsartikel (refereegranskat)abstract
- We have studied GaP/GaAs/GaP and GaAsxP1-x/GaAs/GaAsxP1-x double-barrier resonant tunnelling diodes grown by metalorganic vapor phase epitaxy. We find that GaP tensile strained barriers in GaP/GaAs/GaP diodes may be grown with a barrier thickness below the critical thickness of about 12 monolayers. However, a corrugation of the strained barrier is observed by transmission electron microscopy. This variation may explain the low peak-to-valley ratio of the diodes (about 2). In contrast, GaAsxP1-x/GaAs/GaAsxP1-x resonant tunnelling diodes have been grown with a homogeneous thickness of the barriers, consequently showing a substantially improved electrical performance compared to the GaP diodes with peak-to-valley ratios >5.
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| 2. |
- Fälth, S, et al.
(författare)
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Isolating single selected quantum dots using cryogenic photolithography
- 2002
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Ingår i: PHYSICA SCRIPTA. - 0031-8949 .- 1402-4896. ; T101, s. 133-135
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Konferensbidrag (refereegranskat)abstract
- We propose and demonstrate a technique combining micro-photoluminescence imaging with scanning photolithography at Cryogenic temperatures for creating photoresist masks at designated locations relative to single selected self-assembled quantum dots. The technique is demonstrated by producing a photoresist mask on top of a single selected InP quantum dot imbedded in GaInP. A mesa containing the quantum dot is then created by wet chemical etching. The combination of micro-photoluminescence and scanning photolithography relies on the use of two different lasers with a micro-photoluminescence setup, each laser having different power, focusing and wavelength. The resulting structure enables many experiments and applications in the emerging field of single quantum dot physics.
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| 3. |
- Holm, Magnus, et al.
(författare)
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Calculations of the electronic structure of strained InAs quantum dots in InP
- 2002
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 92:2, s. 932-936
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Tidskriftsartikel (refereegranskat)abstract
- We have calculated the electronic structure of InAs quantum dots embedded in InP as a function of size, using strain dependent eight-band k.p theory in the envelope function approximation. A realistic three-dimensional shape was used for the simulations and the piezoelectric polarization of the system was included. In order to avoid spurious solutions, an extra term was added to the Hamiltonian. Polarization dependent dipole matrix elements were calculated as well as the exciton binding energies. A comparison between measurements and calculated transition energies shows good agreement. (C) 2002 American Institute of Physics.
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| 4. |
- Håkanson, Ulf, et al.
(författare)
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Electric field effects in single semiconductor quantum dots observed by scanning tunneling luminescence
- 2003
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 21:6, s. 2344-2347
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Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy (STM) and scanning tunneling luminescence were used to correlate the topography with the emission spectra from individual self-assembled, InP quantum dots (QDs). We have investigated in detail how the electric field induced by the STM tip affects the emission from the QDs. This was done when exciting a QD, by altering the bias for constant current, by altering the current for constant bias, or by changing the tip position. An increased bias (increased electric field) leads to Stark shift of the QD emission, whereas a larger tunneling current results in state filling of the emission. Furthermore, when exciting the QD, the position of the STM tip is shown to have large effects on the QD luminescence.
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| 5. |
- Håkanson, Ulf, et al.
(författare)
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Photon mapping of quantum dots using a scanning tunneling microscope
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:23, s. 4443-4445
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Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy (STM) and scanning tunneling luminescence (STL) have been used to investigate the geometric and optical properties of individual self-assembled InP quantum dots overgrown with a thin layer of GaInP. STL spectra and monochromatic photon maps were used to correlate the surface topography with the optical properties of single quantum dots. We find a spatial resolution of about 10 nm in the photon maps. Theoretical emission spectra were calculated by six-band k.p theory using a realistic shape of the dot as well as of the cap layer. The calculated emission spectrum of a single dot is in good agreement with the experimental findings. (C) 2002 American Institute of Physics.
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| 6. |
- 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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| 7. |
- Håkanson, Ulf, et al.
(författare)
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Quantum-dot-induced ordering in GaxIn1-xP/InP islands
- 2002
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 66:23
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Tidskriftsartikel (refereegranskat)abstract
- Thin layers of GaxIn1-xP grown on top of self-assembled InP quantum dots has been studied using transmission electron microscopy (TEM), scanning tunneling microscopy (STM), and low-temperature scanning tunneling luminescence (STL). STM reveals that the overgrowth is highly uneven, in which elongated GaxIn1-xP islands covering the dots are formed. TEM and high-spatial-resolution STL show that the quantum dots locally induce domains with higher degree of ordering in the islands. The luminescence from these domains is observed as a strong GaxIn1-xP peak at an energy below the emission from the GaxIn1-xP barrier material.
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| 8. |
- 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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| 9. |
- 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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| 10. |
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