共查询到20条相似文献,搜索用时 15 毫秒
1.
We show how the atomistic pseudopotential many-body theory of InGaAs/GaAs addresses some important effects, including (i) the fine-structure splittings (originating from interband spin exchange), (ii) the optical spectra of charged quantum dots and (iii) the degree of entanglement in a quantum dot molecule. 相似文献
2.
K. D. Osborn Mark W. Keller R. P. Mirin 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):501
A single-electron transistor (SET) is used to detect tunneling of single electrons into individual InGaAs self-assembled quantum dots (QDs). By using an SET with a small island area and growing QDs with a low density we are able to distinguish and measure three QDs. The bias voltage at which resonant tunneling into the dots occurs can be shifted using a surface gate electrode. From the applied voltages at which we observe electrons tunneling, we are able to measure the electron addition energies of three QDs. 相似文献
3.
J. Bosch B. Aln J. Martínez-Pastor D. Granados J.M. García L. Gonzlez 《Superlattices and Microstructures》2008,43(5-6):582
In the presence of a stationary electric field applied in the growth direction tunneling of electrons out of the quantum dots can take place. This mechanism competes with the quantum confined Stark effect (QCSE) that produces an increase of the exciton lifetime by increasing the electric field, mainly due to a net decrease of the electron–hole wavefunction overlap. The electric field range where QCSE dominates over tunneling will be mainly determined by the size of the nanostructure along the vertical direction (height), as demonstrated in this work. 相似文献
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5.
Exciton relaxation in self-assembled semiconductor quantum dots 总被引:1,自引:0,他引:1
Ph. Lelong 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):247
The present study focuses on the effect of excited states on the exciton–polaron spectrum for self-assembled InAs/GaAs semiconductor quantum dots. The analytical model takes into account the Coulomb interactions between the electron and the hole as well as, each carrier, the coupling with the longitudinal optical phonon field. Furthermore, the key role played by the exciton continuum in the dot spectrum is also introduced. Such an approach is well fitted to analyze recent experimental findings about single-dot spectroscopy and allows peaks assignment, line width estimation, relaxation time evaluation, etc., necessary steps toward an understanding of the internal dynamics of quantum dots. 相似文献
6.
A. Hgele B. Aln F. Bickel R. J. Warburton P. M. Petroff K. Karrai 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):175
We show how the resonant absorption of the ground state neutral exciton confined in a single InGaAs self-assembled quantum dot can be directly observed in an optical transmission experiment. A spectrum of the differential transmitted intensity is obtained by sweeping the exciton energy into resonance with laser photons exploiting the voltage induced Stark-shift. We describe the details of this experimental technique and some example results which exploit the 1 μeV spectral resolution. In addition to the fine structure splitting of the neutral exciton and an upper bound on the homogeneous linewidth at 4.2 K, we also determine the transition electric dipole moment. 相似文献
7.
B. Aln K. Karrai R. J. Warburton F. Bickel P. M. Petroff J. Martínez-Pastor 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):395
Excitonic transitions of single InAs self-assembled quantum dots were directly measured at 4.2 K in an optical transmission experiment. We use the Stark effect in order to tune the exciton energy of a single quantum dot into resonance with a narrow-band laser. With this method, sharp resonances in the transmission spectra are observed. The oscillator strengths as well as the homogeneous line widths of the single-dot optical transitions are obtained. A clear saturation in the absorption is observed at modest laser powers. 相似文献
8.
Y. Toda T. Nakaoka R. Morita M. Yamashita T. Inoue Y. Arakawa 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):180
We carried out optical selective excitation of individual self-assembled quantum dots by using phase-modulated pulses. Based on scattered photoluminescence excitation resonances in individual QDs, the excitation pulses modulated in the spectral region allows for addressing individual ground states emission. The photoluminescence spectra including several QDs showed intensity changes according to both the modulation energies and phases. The results also suggested the individual control of selective QDs even in collective excitation. 相似文献
9.
M. S. Jun D. Y. Jeong J. E. Oh S. W. Hwang D. Ahn 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):460
We report electronic characterization of stacked InAs self-assembled quantum dots (SAQDs) embedded in GaAs, using ultra-short pulses. Electrical pulse trains with the width ranging from 50 to 500 ps were applied on the waveguide-type top electrode and the average substrate current was monitored. The current showed staircases and oscillatory features as a function of the pulse width. The staircase could represent single electron injection into SAQDs and the observed oscillatory features could be related with temporal change of electronic occupation in quantum states of SAQDs. 相似文献
10.
Inelastic scattering processes of the two-dimensional electron gas (2DEG) in both normal and inverted n-AlGaAs/GaAs heterojunction FET structures have been studied, for the case where InGaAs dots are embedded in the vicinity of GaAs channel. By analyzing the magnetoresistance data, the inelastic scattering time τin is determined as a function of the concentration N2D of 2D electrons and shown to be reduced by 10–40% by the presence of InGaAs dots. By investigating a GaAs/n-AlGaAs inverted heterojunction FET with embedded InGaAs dots, we have varied the percentage Poc of charged dots filled with an electron and found that τin decreases as Poc increases, indicating that the inelastic scattering rate of 2DEG by charged dots is higher than that by the neutral ones. 相似文献
11.
C. Schulhauser R. J. Warburton A. Hgele A. O. Govorov K. Karrai J. M. Garcia B. D. Gerardot P. M. Petroff 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):184
We report on optical spectroscopy of self-assembled InAs quantum dots in a magnetic field. We describe how we measure the emission characteristics of a single quantum dot (QD) in high magnetic fields at low temperature using a miniature, fiber-based confocal microscope. Example results are presented on a QD whose charge can be controlled using a field-effect device. For the uncharged, singly and doubly charged excitons we find a diamagnetism and the spin Zeeman effect. In contrast, for the triply-charged exciton we find a fundamentally different behavior. Anti-crossings in magnetic field imply that confined states of the QD are hybridized with Landau-like levels associated with the two-dimensional continuum. 相似文献
12.
M. Hayne J. Maes S. Bersier A. Schliwa L. Müller-Kirsch C. Kapteyn R. Heitz D. Bimberg V. V. Moshchalkov 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):189
We explore the Coulomb binding of electrons to holes confined to type-II GaSb self-assembled quantum dots. We demonstrate that at low laser power electrons are more weakly bound to holes trapped by the dots than to holes in the wetting layer. On the other hand, at high laser power the hydrogenic binding energy of dot excitons increases by more than a factor of two, and so exceeds that of wetting layer excitons. We attribute this to the strong binding of ‘core’ electrons to dots that are highly charged with holes by optical pumping. 相似文献
13.
V. A. Tkachenko Z. D. Kvon O. A. Tkachenko D. G. Baksheev O. Estibals J. -C. Portal 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):469
An AlGaAs/GaAs lateral quantum dot of triangular shape with a characteristic size L<100 nm containing less than ten electrons was studied. Single-electron oscillations of the conductance G of this dot were measured at G<e2/h. When going from Ge2/h to G≈0.5e2/h, a decrease was found not only in the amplitude but also in the period of the oscillations. A calculation of the 3D-electrostatics demonstrated that this effect is due to a change in the dot size produced by control voltages. 相似文献
14.
E. A. Zibik L. R. Wilson R. P. Green J. -P. R. Wells P. J. Phillips D. A. Carder J. W. Cockburn M. S. Skolnick M. J. Steer H. Y. Liu M. Hopkinson 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):405
Polaron decay in n-type InAs quantum dots has been investigated using energy dependent, mid-infrared pump–probe spectroscopy. By studying samples with differing ground state to first excited state energy separations the relaxation time has been measured between 40 and 60 meV. The low-temperature decay time increases with increasing detuning between the pump energy and the optical phonon energy and is maximum (55 ps) at 56 meV. From the experimentally determined decay times we are able to extract a low-temperature optical phonon lifetime of 13 ps for InAs QDs. We find that the polaron decay time decreases by a factor of 2 at room temperature due to the reduction of the optical phonon lifetime. 相似文献
15.
S. J. Cheng W. Sheng P. Hawrylak S. Raymond S. Studenikin A. Sachrajda Z. Wasilewski A. Babinski M. Potemski G. Ortner M. Bayer 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):211
We present results of calculations and experiments on electron–hole complexes in InGaAs/GaAs self-assembled quantum dots in high magnetic field (B). Due to hidden symmetries, the chemical potential of an N-exciton system at special B fields becomes insensitive to the exciton number as well as the magnetic field. This results in plateau regions of high intensity in measured magneto-PL spectrum. Theoretical calculations using exact diagonalization techniques successfully explain the measured magneto-photoluminescence spectrum with B fields up to 28 T. 相似文献
16.
A. J. Shields J. L. Osborne M. Y. Simmons D. M. Whittaker F. M. Bolton D. A. Ritchie M. Pepper 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
We study the effect of an electric field applied normal to the layers on the binding energy of charged excitons (or trions) in GaAs quantum wells. We find that, in contrast to the neutral exciton, their binding energy is sharply reduced by modest electric fields. The effect is stronger for the positively charged exciton than the negatively charged one. The ionisation of the excess carrier is explained by the field-induced polarisation of the electron and hole subband wave functions. 相似文献
17.
O. Wibbelhoff C. Meier A. Lorke P. Schafmeister A. D. Wieck 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):516
We use frequency-dependent capacitance–voltage spectroscopy to study the dynamic charging of self-assembled InAs quantum dots. With increasing frequency, the AC charging becomes suppressed, beginning with the low-energy states. By applying an in-plane magnetic field, we generate an additional magnetic confinement that alters the tunneling barrier and hence the charging dynamics. In traveling through the potential barrier, the electrons acquire an additional momentum k0, proportional to the magnetic field B. As the tunneling is enhanced, when k0 matches the maximum of the electronic wave function Ψ (in momentum representation), we are able to map out the shape of Ψ by varying B. 相似文献
18.
K. Ohdaira H. Murata S. Koh M. Baba H. Akiyama R. Ito Y. Shiraki 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):308
Type-I and type-II band alignments were successfully controlled by changing composition and growth temperature in AlInAs/AlGaAs self-assembled quantum dots. The Al composition dependence of the photoluminescence peak shift clearly indicated the crossover from type-I to type-II band line up and a long decay time of 30 ns was obtained by time-resolved photoluminescence at 8 K for the sample with type-II band alignment grown under optimized conditions. A much longer decay component of 500 ns was also observed from the same structure, but it may be due to slow relaxation of carriers trapped in AlGaAs matrix. 相似文献
19.
The transport properties of single InAs quantum dots (QDs) grown by molecular beam epitaxy have been investigated by metallic leads with nanogaps. It was found that the uncapped InAs QDs grown on the GaAs surfaces show metallic conductivities, indicating that even the exposed QDs are not depleted. On the contrary, it was found that no current flows through the exposed wetting layers. For the case of the QDs covered with GaAs capping layers, clear Coulomb gaps and Coulomb staircases have been observed at 4.2 K. 相似文献
20.
R. Brunner R. Meisels F. Kuchar M. ElHassan J. Bird K. Ishibashi 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):491
The properties of open quantum dots are examined in magneto-transport. The quantum dots are prepared from a two-dimensional electron system (2DES) in AlGaAs/GaAs by lateral gate structures. These quantum dots are open, i.e. they are still connected to the surrounding 2DES regions. The low magnetic field magnetoresistance shows peak structures. These structures can be related to semi-classical ballistic trajectories in the confining potential of a dot. The calculations of different confining potentials (abrupt “hard-wall” and parabolic “soft-wall”) are compared with the experimental results. The experiments are better described by a soft-wall potential. 相似文献