| 1. |
- Blomquist, T., et al.
(författare)
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Origin of conductance oscillations in square electron billiards : A semi-classical approach
- 2000
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 6:1, s. 392-395
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Tidskriftsartikel (refereegranskat)abstract
- We perform semi-classical and quantum mechanical calculations on square billiards and provide a semi-classical interpretation of the conductance oscillations. We outline its relation to the Gutzwiller's picture of periodic orbits. The frequencies of the conductance oscillations are shown to be due to interference of pairs of long trajectories, which in the phase space are typically situated near the corresponding periodic orbit. We identify the pair of trajectories causing the pronounced peak in a recent experiment and from this directly extract the phase coherence length.
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| 2. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Evidence for type I band alignment in GaNAs/GaAs quantum structures by optical spectroscopies
- 2002
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 1074-1077
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Tidskriftsartikel (refereegranskat)abstract
- Type I band line-up in GaNxAs1−x/GaAs multiple quantum wells (MQW) with xless-than-or-equals, slant3% is concluded based on the following experimental results: (i) a comparable radiative decay time of the GaNAs-related photoluminescence (PL) measured from single GaNAs epilayers and the GaNAs/GaAs MQW structures, (ii) the observed PL polarization, and (iii) the spatial confinement of photoexcited holes within the GaNAs layers under resonant excitation of the GaNAs MQW.
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| 3. |
- Ekenberg, Ulf, et al.
(författare)
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Control of spontaneous spin splitting in an asymmetric quantum well with the use of strain and/or magnetic field
- 2001
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 10:03-jan, s. 81-85
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Tidskriftsartikel (refereegranskat)abstract
- Spin-orbit coupling combined with inversion asymmetry gives rise to spin splitting even in the absence of an applied magnetic field. The size of this spin splitting can be controlled by changing the degree of asymmetry using a gate voltage. We present here other less obvious ways of controlling the spontaneous spin splitting in a two-dimensional hole gas, where these effects are particularly large. Applying moderate stress can easily decrease the spin splitting by an order of magnitude. The mechanism is the strain-induced energy shift of the heavy-hole and light-hole subbands, which diminishes the degree of band mixing, which is found to be strongly correlated to the spin splitting. An applied magnetic field causes an additional Zeeman splitting, but we find that a magnetic field of 1T can be sufficient to practically erase the difference between a symmetric quantum well (without subband splitting) and an asymmetric quantum well. We have simulated Shubnikov-de Haas oscillations and found that two periodicities in 1/B can occur even for one filled spin-degenerate hole subband.
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| 4. |
- Fu, Y, et al.
(författare)
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Hole conduction characteristics of strained Si1-xGex/Si resonant tunneling diode
- 2002
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier Science B.V., Amsterdam.. - 1386-9477 .- 1873-1759. ; 13:1, s. 72-79
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Tidskriftsartikel (refereegranskat)abstract
- We study the hole conduction characteristics of p-type strained Si1-xGex/Si double-barrier resonant tunneling diodes (RTD). By extensive theoretical calculation of the 6 x 6 k (.) p model together with the deformation potential to account to the strain in Si1-xGex layer, we have obtained the hole conduction characteristics which explains the recent experimental results of Han et al. (J. Cryst. Growth 209 (2000) 315), where it was reported that the low-bias resonance peak becomes dissolved by increasing the device temperature. The calculated I-V characteristics exhibits several resonance peaks, and the current density varies drastically (the second-resonance peak current density is higher than the first one by a factor of 10(3)). Since only resonance peak having high-enough current density is measurable, low-temperature I-V characterization can only dissolve high-bias resonance. Increasing the device temperature, low-bias resonance becomes significant due to thermal excitation.
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| 5. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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The influence of carrier diffusion on the formation of charged excitons in InAs/GaAs quantum dots
- 2002
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 101-104
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Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled quantum dots are very sensitive to the excitation energy and crystal temperature. A qualitative explanation is given in terms of the effective diffusivity of the photogenerated carriers, determined by the experimental conditions, which influence the capture probability and hence also the charge state of the quantum dots (QDs). This is proposed as an effective tool to populate quantum dots with extra electrons in order to study phenomena involving charged excitons. ⌐ 2002 Elsevier Science B.V. All rights reserved.
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| 6. |
- Kemerink, Martijn, et al.
(författare)
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Measuring the potential distribution inside soft organic semiconductors with a scanning-tunneling microscope
- 2002
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 1247-1250
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, we directly measured the potential distribution inside organic semiconductors. Combined spectroscopic measurements are performed on MDMO-PPV layers on Au and Yb substrates, using a scanning-tunneling microscope. The results are analyzed with a model that treats both current injection and bulk transport in detail. It is found that tip height-bias curves, which are taken by following the height of the STM tip as a function of bias, while the STM feedback system is active, reflect the potential distribution between tip and sample electrode. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 7. |
- Kemerink, Martijn, et al.
(författare)
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Quantitative determination of the charge density on surface steps on semiconductors by high-resolution local scanning-tunneling spectroscopy
- 2002
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 1159-1162
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Tidskriftsartikel (refereegranskat)abstract
- A novel technique is developed to follow the energetic position of the conduction and valence bands with respect to the Fermi level as a function of the lateral position on semiconductor surfaces. By combining high-resolution scanning-tunneling spectroscopy measurements with model calculations it is possible to relate the apparent change in conduction and valence band position to their real counterparts. This method allows one to determine the charge on surface artifacts like steps or vacancies, For a single step on p-type GaAs we find a charge of 0.9+/-0.3q nm(-1). (C) 2002 Elsevier Science B.V. All rights reserved.
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| 8. |
- Larsson, Mats, 1976-, et al.
(författare)
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Luminescence study of Si/Ge quantum dots
- 2003
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 16:3-4, s. 476-480
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Tidskriftsartikel (refereegranskat)abstract
- We present a photoluminescence (PL) study of Ge quantum dots embedded in Si. Two different types of recombination processes related to the Ge quantum dots are observed in temperature-dependent PL measurements. The Ge dot-related luminescence peak near 0.80 eV is ascribed to the spatially indirect recombination in the type-II band lineup, while a high-energy peak near 0.85 eV has its origin in the spatially direct recombination. A transition from the spatially indirect to the spatially direct recombination is observed as the temperature is increased. The PL dependence of the excitation power shows an upshift of the Ge quantum dot emission energy with increasing excitation power density. The blueshift is ascribed to band bending at the type-II Si/Ge interface at high carrier densities. Comparison is made with results derived from measurements on uncapped samples. For these uncapped samples, no energy shifts due to excitation power or temperatures are observed in contrast to the capped samples.
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| 9. |
- Mauritz, O., et al.
(författare)
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Magnetic-field-induced suppression of spontaneous spin-splitting of hole subbands
- 2000
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 6:04-jan, s. 779-782
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Tidskriftsartikel (refereegranskat)abstract
- The spin-splitting in the valence band in an InxGa1-xAs/InxGa1-xAsyP1-y quantum well is investigated theoretically using a 6 x 6 Luttinger-Kohn Hamiltonian. We compare the Landau levels in a perpendicular magnetic field with the corresponding results for the subband dispersion;. It is shown that the asymmetry of the quantum well has a very small impact on the Landau level splitting for B > 1 T in sharp contrast to the subbands in the absence of a magnetic field. The significance of our findings on the interpretation of Shubnikov-de Haas experiments is discussed.
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| 10. |
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