| 1. |
- Nakkar, A, et al.
(författare)
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Optical properties and morphology of InAs/InP (113)B surface quantum dots
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:23, s. 3-231911
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Tidskriftsartikel (refereegranskat)abstract
- We report on long-wavelength photoluminescence (PL) emission at room temperature from self-organized InAs surface quantum dots grown by gas-source molecular beam epitaxy on a GaInAsP/InP (113)B substrate. The influence of arsenic pressure conditions during growth on the PL emission of surface quantum dots is detailed as well as oxide/contamination layer formation after growth. Experimental results are in good agreement with six-band k.p theory in the envelope function approximation.
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| 2. |
- Nemec, H., et al.
(författare)
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Bulk-like transversal electron mobility in heavily n-doped InP nanowires probed by terahertz spectroscopy
- 2014
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Ingår i: 2014 39th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2014. - 9781479938773
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Konferensbidrag (refereegranskat)abstract
- Waveguiding of excitation beam and propagation of THz beam in a complex gradient environment were studied in an array of InP nanowires. Measurements by time-resolved THz spectroscopy accompanied by Monte-Carlo calculations of the response of localized charges enabled determination of transversal electron mobility.
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| 3. |
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| 4. |
- Zwiller, Valéry, et al.
(författare)
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Correlation spectroscopy of excitons and biexcitons on a single quantum dot
- 2002
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 66:2, s. 053814-053814-7
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Tidskriftsartikel (refereegranskat)abstract
- We report the observation of antibunched emission from single self-assembled InAs quantum dots under various conditions. We have measured the correlation function of the photon emission pertaining to single emission lines from single quantum dots under continuous and pulsed laser excitation, as well as under continuous white light excitation. The measurements were performed under different excitation intensities at liquid helium temperatures on two samples with distinct structures. At higher temperatures ~30 K!, an antibunching dip was still observed. We have also observed antibunching on a second emission line in the quantum dot spectrum, attributed to the biexciton, demonstrating the possibility of generating photon pairs with a single quantum dot. Polarization correlations on the biexciton and exciton line were also measured in an attempt to generate entangled photon pairs.
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| 5. |
- Geijselaers, Irene, et al.
(författare)
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Radial band bending at wurtzite–zinc-blende–GaAs interfaces
- 2018
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Ingår i: Nano Futures. - : IOP Publishing. - 2399-1984. ; 2:3
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Tidskriftsartikel (refereegranskat)abstract
- The band offset between wurtzite (wz) and zinc-blende (zb) GaAs is an important fundamental parameter in polytype heterostructure engineering. Since the interface has a type-II band alignment, it is reasonably straightforward to measure the band offset using photoluminescence (PL) e.g. on nanowires containing heterostructures between wz and zb GaAs. It has, however, been found that the transition energy in such heterostructures depends on the diameter of the nanowires which introduces uncertainties in the determined value of the band offset. In order to extract a more accurate value and to further elucidate the diameter-dependent behavior of the transition energy we have performed PL studies on a large set of GaAs nanowires. Those nanowires have different diameters and contain one wz–GaAs segment embedded in otherwise zb–GaAs. We have also studied the effect of a passivating capping layer of AlAs on the determined band offset. We find that our data is well explained by a diameter-dependent radial band bending in the nanowires. Combining modeling of the band bending with the experimental data we extract a band offset of about 125 meV and a p-type doping concentration of 1016 cm−3. Our results will improve the accuracy of future modeling of the electronic properties of wz–zb GaAs heterostructures and other engineered polytypic materials.
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| 6. |
- Jash, Asmita, et al.
(författare)
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Excitonic Dynamics at the Type-II Polytype Interface of InP Platelets
- 2023
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Ingår i: ACS Photonics. - 2330-4022. ; 10:9, s. 3143-3148
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Tidskriftsartikel (refereegranskat)abstract
- Indirect excitons are the focus of intense research due to the opportunity of studying degenerate quantum gases and liquids in an excitonic system. To realize such systems, it is highly advantageous to have as little scattering as possible. A polytype type-II interface is formed between wurtzite and zincblende InP due to the band alignment. Electrons gather on the zincblende and holes on the wurtzite side of the interface. Therefore, electrons and holes that are spatially separated by the interface form indirect excitons with aligned dipoles. This polytype type-II interface is perfectly flat, which limits scattering. Here we report that repulsive interaction between the indirect excitons is the driving force behind the long-range transport of indirect excitons along the interface at high exciton densities. This is indicative of less scattering than in conventional type-II heterostructures. The spatial separation of the charge carriers across the interface leads to a low recombination rate of the indirect excitons since the overlap of the electron-hole wavefunction at the interface is small. Emission from the long-lived indirect excitons can be detected even after 40 μs. Our studies have been performed by using spatially and temporally resolved photoluminescence at the low temperature.
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| 7. |
- Jash, Asmita, et al.
(författare)
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Time-resolved photoluminescence studies of single interface wurtzite/zincblende heterostructured InP nanowires
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:11
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Tidskriftsartikel (refereegranskat)abstract
- The interface between wurtzite and zinc blende InP has been identified as type-II, where electrons gather on the zinc blende side and holes on the wurtzite side of the interface. The photoluminescence resulting from recombination across the interface is expected to be long-lived and to exhibit non-exponential decay of emission intensity after pulsed excitation. We verify this prediction using time-resolved photoluminescence spectroscopy on nanowires containing a single heterostructure between a single segment of wurtzite and zinc blende. We find that a significant intensity of type-II emission remains even more than 30 ns after excitation. The decay of the emission intensity is also non-exponential and considerably longer than the exponential decay of the wurtzite InP segment (260 ps). Our results are consistent with the expected photoluminescence characteristics of a type-II interface between the two polytypes. We also find that the lifetime becomes shorter if we create an electron gas at the interface by n-type doping the entire wurtzite segment of the nanowire. This is expected since there are many electrons that a given hole can recombine with, in contrast to the undoped case.
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| 8. |
- Pistol, Mats-Erik, et al.
(författare)
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Random telegraph noise in the photon emission from semiconductor quantum dots
- 2005
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Ingår i: 2005 European Quantum Electronics Conference. - 0780389735 ; , s. 18-18
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Konferensbidrag (refereegranskat)abstract
- This study has observed and investigated random telegraph noise in the photoluminescence from InAs quantum dots in GaAs and InP quantum dots in GaInP. The dots are grown by the Stranski-Krastanow technique with a sufficiently low surface density that individual dots easily could be investigated. The luminescence from many single quantum dots, exhibiting switching between two levels, has been spectrally resolved as a function of time. The random telegraph noise is only observed in the presence of band filling. Results show no spectral shift of the emission in the different states. It is only the intensity, mainly for higher energy peaks that changes. The InAs quantum dots behave very similarly to InP/GaInP and InGaAs/GaAs quantum dots with respect to random telegraph noise. The similarities between the different systems argue for a common mechanism behind the blinking. Experiments are performed where the switching behaviour is changed in all the different systems supporting the idea that non-radiative defects are responsible
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| 9. |
- Tatte, T, et al.
(författare)
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Metal oxide based SPM tips prepared by sol-gel method
- 2002
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Ingår i: Physics of Low-Dimensional Structures. - 0204-3467. ; 5-6, s. 31-37
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Tidskriftsartikel (refereegranskat)abstract
- Up to date SNOM tips have. been prepared from SiO2 based materials using etching or locally melt fibre's stretching for tip sharpening [1,2] Usage of other metal oxides has been restricted because of the lack Of methods for obtaining the tips with suitable geometrical configuration. In our previous work we have proposed the technique for preparing transparent and electroconductive SnO2 fibres and tips by sol-gel method [3]. In the present investigation we have demonstrated that the sol-gel method provides the wide range of metal oxides to obtain SPM fibre tips. The new method of preparation enables to study tips based on oxide or oxide mixtures to create sensors with new properties for different applications. We propose some methods for preparing suitable precursors for spinning of pure and mixed TiO2, SnO2, SiO2 fibres. In those new methods the sharpening of tips is achieved in fibre drawing procedure. That is carried out at room temperature in humid atmosphere and then fibres are baked at 300-700degreesC for crystallisation of the material.
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| 10. |
- Tatte, T, et al.
(författare)
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Transparent and conductive Sb-doped tin oxide SPM tips prepared by sol-gel method
- 2002
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Ingår i: Materials Science and Engineering C: Materials for Biological Applications. - 0928-4931. ; 19:1-2, s. 101-104
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Tidskriftsartikel (refereegranskat)abstract
- The rapid progress in scanning probe microscopy (SPM) techniques in the last decade has induced an increasing need for manufacturing advanced SPM tips. One important case is conductive and transparent tips. For such tips, only a few techniques have been proposed. which are either expensive or have poor reproducibility. We here propose a simple and cheap sol-gel technique to prepare fibers with a suitably sharp apex so that they can be used as SPM tips. The fibers were spinned off from a high-viscosity solution of tin alkoxide and SbCl3 hydrolysed in hurnid air and baked at 520 degreesC for several hours. The radii of the resulting tips were estimated by transmission electron microscopy to be less than 50 am. The resistivity of the transparent fibers was measured using different Sb-doping (0.5-1 wt.%) of the tin oxide, The temperature dependence of the conductivity and light absorption were investigated down to liquid He temperatures.
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| 11. |
- Vainorius, Neimantas, et al.
(författare)
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Non-resonant Raman scattering of wurtzite GaAs and InP nanowires
- 2020
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Ingår i: Optics Express. - 1094-4087. ; 28:8, s. 11016-11022
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Tidskriftsartikel (refereegranskat)abstract
- It is now possible to synthesize the wurtzite crystal phase of most III-V semiconductors in the form of nanowires. This sparks interest for fundamental research and adds extra degrees of freedom for designing novel devices. However, the understanding of many properties, such as phonon dispersion, of these wurtzite semiconductors is not yet complete, despite the extensive number of studies published. The E2 L and E2 H phonon modes exist in the wurtzite crystal phase only (not in zinc blende) where the E2 H mode has been already experimentally observed in Ga and In arsenides and phosphides, while the E2 L mode has been observed in GaP, but not in GaAs or InP. In order to determine the energy of E2 L in wurtzite GaAs and InP, we performed Raman scattering measurements on wurtzite GaAs and InP nanowires. We found clear evidence of the E2 L phonon mode at 64 cm−1 and 54 cm−1, respectively. Polarization-dependent experiments revealed similar selection rules for both the E2 L and the E2 H phonon modes (as expected) where the intensity peaked with excitation and detection polarization being perpendicular to the [0001] crystallographic direction. We further find that the splitting between the E1(TO) and A1(TO) modes is around 2 cm−1 in wurtzite GaAs and below 1 cm−1 in wurtzite InP. We believe these results will be useful for a better understanding of phonons in wurtzite crystal phase of III-V semiconductors as well as for testing and improving phonon dispersion calculations.
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| 12. |
- Vainorius, Neimantas, et al.
(författare)
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Wurtzite GaAs Quantum Wires : One-Dimensional Subband Formation
- 2016
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:4, s. 2774-2780
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Tidskriftsartikel (refereegranskat)abstract
- It is of contemporary interest to fabricate nanowires having quantum confinement and one-dimensional subband formation. This is due to a host of applications, for example, in optical devices, and in quantum optics. We have here fabricated and optically investigated narrow, down to 10 nm diameter, wurtzite GaAs nanowires which show strong quantum confinement and the formation of one-dimensional subbands. The fabrication was bottom up and in one step using the vapor-liquid-solid growth mechanism. Combining photoluminescence excitation spectroscopy with transmission electron microscopy on the same individual nanowires, we were able to extract the effective masses of the electrons in the two lowest conduction bands as well as the effective masses of the holes in the two highest valence bands. Our results, combined with earlier demonstrations of thin crystal phase nanodots in GaAs, set the stage for the fabrication of crystal phase quantum dots having full three-dimensional confinement.
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