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ABSTRACT: We have investigated the electronic structure of excitons in InP quantum dots in GaInP. The exciton is theoretically expected to have four states. Two of the states are allowed to optically decay to the ground (vacuum) state in the dipole approximation. We see these two lines in photoluminescence (PL) experiments and find that the splitting between the lines (the fine structure splitting) is 150(± 30) µeV. The lines were perpendicularly polarized. We verified that the lines arise from neutral excitons by using correlation spectroscopy. The theoretical calculations show that the polarization of the emission lines are along and perpendicular to the major axis of elongated dots. The fine structure splitting depends on the degree of elongation of the dots and is close to zero for dots of cylindrical symmetry, despite the influence of the piezoelectric polarization, which is included in the calculation.
Journal of Physics Condensed Matter 07/2007; 19(29):295211. · 2.55 Impact Factor
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ABSTRACT: We have fabricated InAs dots on the surface of InP, determined their structure, and measured the optical transition energy. This energy was found to be in excellent agreement with theoretical calculations, where no free parameters have been used. The calculations were performed using eight-band k ∙ p theory in the envelope function approximation. We conclude that this theory is adequate to describe quantum dots also when one of the confining materials is vacuum.
Applied Physics Letters 08/2006; · 3.84 Impact Factor
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ABSTRACT: SiGe Esaki diodes have been realized by rapid thermal diffusion of phosphorous into an SiGe layer grown by ultra-high-vacuum chemical-vapor-deposition on an Si p<sup>+</sup>-substrate for the first time. The phosphorous-doped SiGe forms the n<sup>+</sup>-electrode, while heavily boron-doped Si<sub>0.74</sub>Ge<sub>0.26</sub> and Si substrate is used for the p<sup>+</sup> electrode. The diodes show a peak current density of 0.18 kA/cm<sup>2</sup>, a current peak-to-valley ratio of 2.6 at room temperature, and they exhibit only a weak temperature dependence. Cross-sectional transmission microscopy showed a good crystalline quality of the strained Si<sub>0.74</sub>Ge<sub>0.26</sub> layer even after the diffusion step at 900°C.
IEEE Transactions on Nanotechnology 10/2005; · 2.29 Impact Factor
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Advanced Functional Materials 08/2005; 15(10):1603 - 1610. · 10.18 Impact Factor
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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.
Quantum Electronics Conference, 2005. EQEC '05. European; 07/2005
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ABSTRACT: The growth behaviour of Au-catalyzed III-V semiconductor nanowires and nanotrees is strongly affected by the temperature dependent interaction between the catalytic Au particle and the particular III-V material
Indium Phosphide and Related Materials, 2005. International Conference on; 06/2005
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ABSTRACT: We demonstrate metal organic vapour phase epitaxy growth of GaP/GaAs1−xPx/GaP double heterostructure nanowires on GaP(111)B, and report bright photoluminescence at room temperature. By using different PH3 to AsH3 flow ratios during growth of the GaAs1−xPx segment, we are able to control the composition of the segment, making it feasible to tune the wavelength of the emitted light. A photoluminescence system was employed to characterize the luminescence, and x-ray energy dispersive spectrometry and x-ray diffraction studies were used to investigate the composition of the segment. These double heterostructure nanowires could in the future be used in optoelectronic devices and as multiple-wavelength fluorescent markers for biomedical applications.
Nanotechnology 04/2005; 16(6):936. · 3.98 Impact Factor
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ABSTRACT: Using an approach of combining Fourier transform infrared spectroscopy with resonant illumination from a secondary external light source, we have measured the photocurrent (PC) for multiple layers of self-assembled InAs dots embedded in a matrix of InP. Without external illumination, we observe photoexcitation of electrons from bound states in the dots to the InP barrier. By additional illumination from the external light source, a strong broadening of the PC signal is observed. We interpret this broadening in terms of photoexcitation of electrons in the presence of additional holes in the dots created by the external light source. We extract the spectral distribution of the photoexcitation process at 6 and 77 K, respectively, and show by comparison with theoretical calculations that it is consistent with an exciton binding energy of 20 meV.
Applied Physics Letters 11/2004; 85(21):5046-5048. · 3.84 Impact Factor
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ABSTRACT: Semiconductor nanowires are grown using chemical beam epitaxy and metal organic vapor phase epitaxy from size‐selected gold nanoparticles acting as catalysts. By changing materials during the growth it is possible to form heterostructures both along the length of the nanowires but also in a core‐shell fashion. In particular, incorporation of pairs of InP tunnel barriers in InAs nanowires has been used to fabricate single‐electron transistors and resonant tunneling diodes. © 2004 American Institute of Physics
AIP Conference Proceedings. 09/2004; 723(1):449-454.
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P. Carlberg,
F. Johansson,
T. Martensson,
R. Bunk,
M. Beck,
F. Persson,
M. Borgstrom,
S.G. Nilsson,
B. Heidari,
M. Grazcyk,
I. Maximov,
E.-L. Sarwe,
T.G.I. Ling,
A. Mansson,
M. Kanje, W. Seifert,
L. Samuelson,
L. Montelius
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ABSTRACT: In this paper, we present a status report on how implementation of nanoimprint lithography has advanced our research. Contact guidance nerve growth experiments have so far primarily been done on micrometer-structured surfaces. We have made a stamp with 17 areas of different, submicron, line width and spacing covering a total 2.6 mm×0.45 mm. This has been imprinted, in PMMA, and consequently used in experiments to investigate how axonal outgrowth is affected by the nanopatterns. Protein interactions with nanostructured surfaces are also studied in a system exploring and controlling biomolecular motors, i.e., the muscle motor proteins actin and myosin.
Nanotechnology, 2004. 4th IEEE Conference on; 09/2004
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ABSTRACT: We report on [001] InP nanowires grown by metalorganic vapor phase epitaxy directly on (001) InP substrates. Characterization by scanning electron microscopy and transmission electron microscopy reveals wires with nearly square cross sections and a perfect zinc-blende crystalline structure that is free of stacking faults. Photoluminescence measurements of single [001] nanowires exhibit a narrow and intense emission peak at approximately 1.4 eV, whereas 〈111〉B grown reference wires show additional broad luminescence peaks at lower energy. The origin of this uncommon wire growth direction [001] is discussed as a means of controlled formation of [00l]-oriented nanowires on (001) substrates.
Applied Physics Letters 09/2004; 85(11):2077-2079. · 3.84 Impact Factor
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ABSTRACT: We report on a detailed investigation of the interband optics of self-assembled InAs dots embedded in a matrix of InP. In photoconductivity (PC) measurements, we observe optical processes related to the dots and a wetting layer, band-to-band excitation of the InP barrier, as well as to an interesting As-related impurity. In particular, the PC measurements reveal the electronic structure of the dots and strongly suggest that an Auger effect is involved in forming the PC signal. Comparing the PC and photoluminescence (PL) signals, we observe that the fundamental transition is not observed in PC, which we interpret in terms of Pauli blocking due to electrons populating the ground state of the dots. In general, it is demonstrated that the PC technique is in many respects complementary to PL and gives additional insight into the electronic structure of quantum dots. © 2004 American Institute of Physics.
Journal of Applied Physics 06/2004; 95(12):8007-8010. · 2.17 Impact Factor
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ABSTRACT: In this letter, we demonstrate the realization of novel diodes, triodes, and logic gates with three-terminal ballistic junctions (TBJs) made from a semiconductor heterostructure. The approach exploits the ballistic nature of electron transport, which has emerged in the nanostructures. Importantly, we show that TBJs function as logic AND gates and can be used to construct other compound logic gates, such as NAND gates with voltage gain, when combined with a point contact (an inverter). The demonstrated devices show favorable characteristics such as low turn-on voltage in rectification and room-temperature operation.
IEEE Electron Device Letters 05/2004; · 2.85 Impact Factor
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ABSTRACT: In this article, we present the results from photoconductivity measurements in the infrared spectral region (3–10 μm) on ensembles of self-assembled InAs quantum dots embedded in a matrix of InP. In the spectral distribution of the photocurrent, peaks are observed which we interpret in terms of transitions from the dots’ ground- and first-excited states to the conduction band of the dots/matrix. Furthermore, we have calculated the expected photoresponse and found it to be in qualitative agreement with our experimental data. © 2004 American Institute of Physics.
Journal of Applied Physics 02/2004; 95(4):1829-1831. · 2.17 Impact Factor
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ABSTRACT: A process for realisation of SiGe Esaki diodes in layers grown by ultra-high vacuum chemical vapour deposition has been developed and the first Esaki diodes are reported for this growth method. Intrinsic SiGe-layers are grown on highly boron-doped p<sup>+</sup>-Si layers, while post-growth proximity rapid thermal diffusion of phosphorous into the SiGe is employed to form an n<sup>+</sup>-layer. Tunnel diodes with a depletion layer width of about 6 nm have been realised in Si<sub>0.74</sub>Ge<sub>0.26</sub>, showing a peak current density of 0.18 kA/cm<sup>2</sup> and a current peak-to-valley ratio of 2.6 at room temperature.
Electronics Letters 02/2004; · 0.96 Impact Factor
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ABSTRACT: In this paper we show that SiGe Esaki diodes can be fabricated by ultra-high vacuum chemical vapor deposition (UHV-CVD), which opens a new possibility for the integration of the diodes into VLSI-circuits. Generally, UHV-CVD produces sharp heterostructure interfaces, high B-doping levels and abrupt doping profiles, which are crucial for the Esaki diodes. The ultra shallow junction is formed via proximity diffusion of P in a rapid thermal process using a spin-on dopant source. We compare data for diodes diffused under various conditions, including diodes where we etched off the top Si cap layer with a selective etch. The calculated band structures are shown.
Semiconductor Device Research Symposium, 2003 International; 01/2004
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L Samuelson,
C Thelander,
M T Bj,
Ork,
M Borgstr,
Om,
K Deppert,
K A Dick,
A E Hansen,
T M Artensson,
N Panev,
A I Persson, W Seifert,
N Sk,
Old,
M W Larsson,
L R Wallenberg
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ABSTRACT: During the last 5 years the potential for applications of semiconductor nanowires has grown rapidly via the development of methods for catalytically induced nanowire growth using the, so-called vapor–liquid–solid (VLS) growth mode. The VLS method offers a high degree of control of parameters such as position, diameter, length and composition, including the realization of atomically abrupt heterostructure interfaces inside a nanowire. In this review, we summarize the progress and the standing of our research from the point of view of controlled growth, structural and electronic properties and in terms of different families of devices which have been possible to realize. r 2004 Elsevier B.V. All rights reserved.
67.Lt. 01/2004; 736323(73).
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ABSTRACT: We present a new type of nanometer-scale semiconductor nonlinear device, called self-switching device (SSD). The device was realized by simply etching insulating grooves into a semiconductor, between which a narrow channel with a broken symmetry was formed. Because of the asymmetry in the channel boundary, an applied voltage V not only changes the potential proÿle along the channel direction, but also either widens or narrows the eeective channel width depending on the sign of V . This results in a diode-like current–voltage characteristic but without the use of any doping junction or barrier structure. The turn-on voltage can also be widely tuned from virtually 0 to more than 10 V by simply adjusting the channel width. Furthermore, only one lithography step was needed to fabricate SSDs. We used two diierent material systems, InGaAs–InP and InGaAs–InAlAs, to realize SSDs and the results at room temperature were compared. We also show that by adding a third terminal to an SSD as a gate, the turn-on voltage of the device could be tuned by the gate bias and the device functions either as a tunable diode or as a transistor.
40.Ei35.Be. 01/2004; 85(73).
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ABSTRACT: We report on a method of synthesizing arrays of individually seeded nanowires. An electron beam lithography and metal lift-off method was used to pattern InP(111)B substrates with catalysing gold particles. Vertical nanowire arrays were then grown from the gold particles, using metal–organic vapour phase epitaxy. The lithographic nature of the method allows individual control over each nanowire. Possible applications for such deterministic and uniform arrays include producing arrays of nanowire devices, two-dimensional photonic band gap structures and field emission displays, amongst others.
Nanotechnology 10/2003; 14(12):1255. · 3.98 Impact Factor
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ABSTRACT: By tailoring the boundary of a narrow semiconductor channel to break its symmetry, we have realized a type of nanometer-scale nonlinear device, which we refer to as self-switching device (SSD). An applied voltage V not only changes the potential profile along the channel direction, but also either widens or narrows the effective channel depending on the sign of V. This results in a diode-like characteristic but without the use of any doping junction or barrier structure. The turn-on voltage can also be widely tuned from virtually zero to more than 10 V, by simply adjusting the channel width. The planar and two-terminal structure of the SSD also allows SSD-based circuits to be realized by only one step of lithography. © 2003 American Institute of Physics.
Applied Physics Letters 08/2003; 83(9):1881-1883. · 3.84 Impact Factor
