共查询到20条相似文献,搜索用时 31 毫秒
1.
L. E. Vorob’ev V. Yu. Panevin N. K. Fedosov D. A. Firsov V. A. Shalygin S. Hanna A. Seilmeier Kh. Moumanis F. Julien A. E. Zhukov V. M. Ustinov 《Physics of the Solid State》2004,46(1):118-121
High-resolution spectroscopy in the mid-infrared spectral range is used to study electronic transitions between size-quantization subbands in stepped quantum wells under picosecond interband excitation. The contributions from intersubband and intrasubband absorption of light are separated by using the difference in time profiles of the absorption coefficient for these cases. For stepped quantum wells, spontaneous interband luminescence and superluminescence are studied for different excitation levels. For structures with quantum dots, the intraband absorption spectra for n-and p-type structures and the spectra of photoinduced intraband absorption and emission (for polarized radiation) for undoped structures are studied. 相似文献
2.
Intraband optical transitions in semiconductor quantum dots (QDs) in the forms of a parallelepiped, sphere, and cylinder have
been considered. It is shown that the size dependence of the matrix elements of electron-photon interaction, which includes
the intraband transitions, differs in the E · r and A · p representations of electron-photon coupling, which are widely used to describe various optical processes. The radiative intraband
relaxation rates of QD electron excitations have been calculated, depending on the QD size and shape and the parameters of
the QD material. It is shown that the radiative intraband transition rate may reach 109 s−1. 相似文献
3.
A. B. Dzyubenko 《Journal of Experimental and Theoretical Physics》1998,86(4):790-797
A theory of far-infrared (FIR) magneto-optical intraband s→p
± transitions of direct and indirect excitons in semiconductor coupled double quantum wells has been developed. The case of
symmetric strained InxGa1−x
As/GaAs quantum wells with nondegenerate valence band in the regime of both narrow and wide barriers has been analyzed. The
energies and dipole matrix elements of transitions between the ground s and excited p
± states in a quantizing magnetic field B>2 T and electric field ℰ perpendicular to the quantum well plane have been studied. The regimes of direct (in a weak electric
field) and indirect (in a strong electric field) transitions, and the transition between the direct and indirect regimes,
have been investigated.
Zh. éksp. Teor. Fiz. 113, 1446–1459 (April 1998) 相似文献
4.
L. E. Vorob’ev D. A. Firsov V. A. Shalygin V. N. Tulupenko Yu. M. Shernyakov N. N. Ledentsov V. M. Ustinov Zh. I. Alferov 《JETP Letters》1998,67(4):275-279
The spontaneous emission of far-infrared radiation (λ≅10–20 μm) from diode structures with vertically coupled InGaAs/AlGaAs
quantum dots is observed. This emission is due both to transitions of holes and electrons between size-quantization levels
in quantum dots and to transitions from the continuum to a level in a quantum dot. It is observed only when accompanied by
lasing at short wavelengths (λ≅0.94 μm) and, like the short-wavelength emission, it exhibits a current threshold. The spontaneous
emission of long-wavelength radiation is also observed in InGaAs/GaAs quantum-well laser structures. This radiation is approximately
an order of magnitude weaker than that from quantum-dot structures, and it has no current threshold.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 4, 256–260 (25 February 1998) 相似文献
5.
V. Ya. Aleshkin A. A. Andronov A. V. Antonov N. A. Bekin V. I. Gavrilenko D. G. Revin B. N. Zvonkov E. R. Lin’kova I. G. Malkina E. A. Uskova 《JETP Letters》1996,64(7):520-524
The infrared radiation from hot holes in InxGa1−x
As/GaAs heterostructures with strained quantum wells during lateral transport is investigated experimentally. It is found
that the infrared radiation intensities are nonmonotonic functions of the electric field. This behavior is due to the escape
of hot holes from quantum wells in the GaAs barrier layers. A new mechanism for producing a population inversion in these
structures is proposed.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 478–482 (10 October 1996) 相似文献
6.
Raman scattering of light by optical phonons in Si-Ge-Si structures with pseudomorphic germanium quantum dots has been investigated.
Resonance amplification of the scattering intensity on E
0 (Γ7−Γ8) transitions has been observed. It is shown that as a result of the formation of the layer of germanium quantum dots, the
resonance energy is ∼0.3 eV higher than in the two-dimensional case.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 203–207 (10 August 1996) 相似文献
7.
V. A. Kovarskii 《JETP Letters》1997,65(2):215-216
Quantum dots based on materials with long-lived terahertz vibrations are studied. It is shown that squeezed states of such
vibrations can result in microwave-frequency modulation of the optical radiation absorbed at electronic transitions in quantum
dots.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 2, 199–200 (25 January 1997) 相似文献
8.
Summary We show how the breaking of the translational invariance in a quantum well modifies the concept of polariton with respect
to that defined for bulk material. Polaritons in quantum wells result from the combination of the exciton states with the
radiation field. They are here obtained as the solutions of Maxwell equations with retardation, provided an appropriate nonlocal
response function is used for the electric susceptibility, and Maxwell boundary conditions are imposed. We find two types
of polaritons depending on the values of the in-plane wavevectork
II: those atk
II<ω/v (wherev=c/n is the velocity of light in the sample) are resonant with the radiation field in the barrier and those atk
II>ω/v cannot be coupled to waves in the barrier. In both cases explicit expressions are given for radiative shifts and radiative
broadenings as functions ofk
II. Numerical results are obtained for GaAs-Ga1−x
Al
x
As and for CuCl quantum wells and new experiments are suggested. The existence of resonant and surface polaritons justifies
an interpretation of the temperature dependence of the radiative lifetime suggested by the same authors. It also decreases
the radiative efficiency in the direction perpendicular to the planes and increases the radiative efficiency parallel to the
planes with increasing temperature.
Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction. 相似文献
9.
A Mott exciton in coupled quantum wells in a transverse magnetic field H is considered. An expression for the exciton spectrum in an arbitrary magnetic field for large separations D between quantum wells containing an electron (e) and a hole (h) is given. The exciton spectrum in a strong magnetic field for different Landau levels at arbitrary D has been calculated. Changes in the parameter D/l, where
is the magnetic length, cause rearrangement of the magnetoexciton dispersion curves ℰ(P), where P is the conserved “magnetic” momentum, which is a function of the separation between the electron and hole in the plane of
the quantum wells. Off-center (“roton”) extrema occur only for D/l,<(D/l)cr, where (D/l)cr is a function of the exciton quantum numbers n and m. The magnetoexciton effective mass in states with magnetic quantum number m=0 monotonically increases with H and D, while in states with m≠0 it is a nonmonotonic function of D/l. The probability of generating an exciton in coupled quantum wells increases with H. Absorption of electromagnetic radiation due to transitions between excitonic levels in coupled quantum wells is discussed.
For an exciton containing a heavy hole the oscillator strengths
increase with H and the oscillator strengths
decrease.
Zh. éksp. Teor. Fiz. 112, 1791–1808 (November 1997) 相似文献
10.
V. B. Timofeev A. V. Larionov P. S. Dorozhkin M. Bayer A. Forchel J. Straka 《JETP Letters》1997,65(11):877-882
When a voltage is applied to double quantum wells based on AlGaAs/GaAs heterostructures with contact regions (n-i-n structures), a two-dimensional (2D) electron gas appears in one of the quantum wells. Under illumination which generates
electron-hole pairs, the photoexcited holes become localized in a neighboring quantum well and recombine radiatively with
the 2D electrons (tunneling recombination through the barrier). The appearance, ground-state energy, and density of the degenerate
2D electron gas are determined from the structure of the Landau levels in the luminescence and luminescence excitation spectra
as well as from the oscillations of the radiative recombination intensity in a magnetic field with detection directly at the
Fermi level. The electron density is regulated by the voltage between the contact regions and increases with the slope of
the bands. For a fixed slope of the bands the 2D-electron density has an upper limit determined by the resonance tunneling
of electrons into a neighboring quantum well and subsequent direct recombination with photoexcited holes.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 840–845 (10 June 1997) 相似文献
11.
A. Urbina C. Díaz-Paniagua A.F. Braña F. Batallán 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):463-468
We present measurements of the diagonal Rxx and off-diagonal Rxy magnetoresistance under quantum Hall conditions on several high electron mobility transistors (HEMT) based on InxGa1-xAs quantum wells. From the magnetoresistance tensor we obtain the longitudinal conductivity σ
xx
. We study the transport mechanisms near the σ
xx
minima at temperatures ranging between 2 K and 35 K; activated transport is the dominant mechanism for temperatures above
7 K while variable range hopping conductivity is significant for lower temperatures. We show that electron-electron correlations
should be taken into account to explain the conductivity vs temperature behaviour below 5 K. Finally, we study the behaviour of the localization length as a function of Landau level
filling and obtain a critical exponent γ = 3.45±0.15.
Received 6 June 2001 and Received in final form 16 October 2001 相似文献
12.
Nirmal Misra Mohendra Roy Dambarudhar Mohanta Kishor Kumar Baruah Amarjyoti Choudhury 《Central European Journal of Physics》2008,6(1):109-115
ZnO:Mn semiconductor quantum dots were prepared by solution casting led microemulsion route. Quantum dots of average size
∼2 nm were noticed in transmission electron micrographs. The present work highlights colour change phenomena (photochromic
effect) of quantum dots while subjected to photon illumination. The magneto-optic measurements e.g. magnetic field (H) vs angle of rotation (θ) show step like behavior and is ascribed to the quantum confinement effect of diluted magnetic ZnO:Mn nanostructures. Further,
underlying mechanism responsible for exhibiting photochromism and magneto-optic effects are also discussed.
相似文献
13.
《Superlattices and Microstructures》1995,17(1):41-45
The bleaching bands have been observed in the time-resolved nonlinear transmission spectra of porous silicon. The increase of transmission at discrete frequencies has been attributed to a saturation of optical transitions between the energy levels of electrons and holes spatially confined within quasi-zero-dimensional (quantum dots) and quasi-one-dimensional (quantum wires) nanostructures. The results of independent measurements using transmission electron microscopy have confirmed the existence of quantum dots and wires of corresponding size. The slowed-down energy relaxation from upper to lower levels of size quantization compared with intraband relaxation in the bulk have been observed in the cooled (80K) platelets of porous silicon. 相似文献
14.
D. V. Dmitriev I. S. Strygin A. A. Bykov S. Dietrich S. A. Vitkalov 《JETP Letters》2012,95(8):420-423
Low-temperature dependences of the transport relaxation time (τtr) and quantum lifetime (τq) on the density of the two-dimensional electron gas (n e ) in GaAs quantum wells with AlAs/GaAs lateral superlattice barriers have been studied. An exponential increase in the quantum lifetime with increasing electron density has been observed. It has been shown that the sharp increase in the quantum lifetime correlates with the appearance of X electrons in the AlAs/GaAs lateral superlattice barriers. It has been established that the ratio of the transport relaxation time to the quantum lifetime in the studied structures nonmonotonically depends on the density: the ratio τtr/τq first increases linearly with n e and then decreases. This behavior is not described by the existing theories. 相似文献
15.
Liming Liu Junjie Li Guiguang Xiong 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):466-471
The resonant third-order susceptibilities at various directions (both parallel and vertical to Z-axis) in self-assembled quantum dots (QDs) have been investigated. The nonlinear susceptibilities associated with the intraband transition in the conduction band are theoretically calculated for wurtzite InxGa1−xN/GaN-strained cylinder QDs. The confined wave functions and energies of electrons in the dots have been calculated in the effective-mass approximation by solving the 3D Schrödinger equation, in which a strong built-in electric field effect due to the piezoelectricity and spontaneous polarization has been taken into account. Furthermore, it is shown that the magnitude and the resonant position of the nonlinear susceptibility χ(3)(3ω) strongly depend on the dots’ size as well as size distribution. 相似文献
16.
In this work, we have studied the inter- and intra-subband scattering of hot electrons in quantum wells using the hot electron-neutral acceptor luminescence technique. We have observed direct evidence of the emission of confined optical phonons by hot electrons excited slightly above the n=2 subband in GaAs/Al0.37Ga0.63As quantum wells. Scattering rates of photoexcited electrons via inter- and intra-subband LO phonon emission were calculated based on the dielectric continuum model. We found that, for wide wells with the Al composition of our experiments, both the calculated and experimental results suggest that the scattering of the electrons is dominated by the confined LO phonon mode. In the calculations, scatterings among higher subbands are also dominated by the same type of phonon at well width of 10 nm. 相似文献
17.
K. Mathan Kumar A. John Peter C. W. Lee 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(3):431-438
Electronic energies of an exciton confined in a strained
Zn1−x
Cd
x
Se/ZnSe quantum dot have
been computed as a function of dot radius with various Cd content. Calculations have been
performed using Bessel function as an orthonormal basis for different confinement
potentials of barrier height considering the internal electric field induced by the
spontaneous and piezoelectric polarizations. The optical absorption coefficients and the
refractive index changes between the ground state (L = 0) and the first
excited state (L = 1) are investigated. It is found that the optical
properties in the strained ZnCdSe/ZnSe quantum dot are strongly affected by the
confinement potentials and the dot radii. The intensity of the total absorption spectra
increases for the transition between higher levels. The obtained optical nonlinearity
brings out the fact that it should be considered in calculating the optical properties in
low dimensional semiconductors especially in quantum dots. 相似文献
18.
The observation of optical orientation of excitons and the Hanle effect in an asymmetric CdTe/CdMnTe double quantum well is
reported. The characteristics of the magnetic depolarization of radiation from CdTe/CdMnTe quantum wells are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 241–245 (25 February 1996) 相似文献
19.
Quantum crystallization of electrons in a quantum dot (QD) subjected to an external magnetic field is considered. Two-electron
QDs with two-dimensional (2D) parabolic confining potential in an external transverse magnetic field are calculated. The Hamiltonian is numerically diagonalized
in the basis of one-particle functions to find the energy spectra and wave functions for the relative motion of electrons
with inclusion of electron-electron interaction for a broad range of the confining-potential steepness (α) and external magnetic fields (B). The region of the external parameters (α, B) within which a gradual transition to quantum crystalline order occurs is numerically determined. In contrast to a 2D unbounded system, a magnetic field acts nonmonotonically on “crystallization” in a quantum dot with several electrons because
of a competition between two effects taking place with increasing B, namely, decreasing spread of the electron wave functions and increasing effective steepness of the confining potential,
which reduces the average separation between electrons.
Fiz. Tverd. Tela (St. Petersburg) 40, 1753–1759 (September 1998) 相似文献
20.
The changes in the birefringence and absorption of infrared radiation accompanying direct electron transitions induced between
size-quantization subbands in a GaAs/AlGaAs system of doped quantum wells by heating of the electrons by an electric field
applied parallel to the layers of the heterostructure are observed and investigated. An explanation of the observed effects
is offered whereing the change in the absorption spectrum and the contribution of free electrons to the permittivity are related
to the exchange interaction and nonparabolicity of the energy spectrum of the hot electrons.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 525–530 (10 April 1997) 相似文献