Showing papers on "Quantum dot published in 1990"
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01 Apr 1990
TL;DR: In this article, a revised second edition on the "Quantum Theory of the Optical and Electronic Properties of Semiconductors" presents the basic elements needed to understand and engage in research in semiconductor physics.
Abstract: This revised second edition on the "Quantum Theory of the Optical and Electronic Properties of Semiconductors" presents the basic elements needed to understand and engage in research in semiconductor physics. In this revised second edition misprints are corrected and some new and more detailed material is added. In order to treat the valence-band structure of semiconductors, an introduction to the k.p. theory and the related description in terms of the Luttinger Hamiltonian is included. An introductory chapter on mesoscopic semiconductor structures discussing the modifications of the envelope function approximation caused by the spatial quantum confinement is also included. Many results are developed in parallel first for bulk material, and then for quasi-two-dimensional quantum wells, and for quasi-one-dimensional quantum wires. Semiconductor quantum dots are treated in a separate chapter. The discussion of time-dependent and coherent phenomena in semiconductors has been considerably extended by including a section dealing with the theoretical description of photon echoes in semiconductors. A new chapter on magneto-absorption has been added, in which magneto-excitons and magneto-plasmas in two-dimensional systems are discussed. The chapter on electron kinetics due to the interaction with longitudinal-optical phonons has been extended. The material is presented in sufficient detail for graduate students and researchers who have a general background in quantum mechanics, and is aimed at solid state physicists, engineers, materials and optical scientists.
2,492 citations
TL;DR: In this paper, it was observed that the optical spectra of a nanometer-sized semiconductor crystallite are sensitive to size and the number of atoms in the crystallite.
Abstract: How can one understand the excited electronic states of a nanometer sized semiconductor crystallite, given that the crystallite structure is simply that of an excised fragment of the bulk lattice? This question is motivated by recent experiments on chemically synthesized "quantum crystallites," sometimes called "quantum dots," in which it is observed that the optical spectra are quite sensitive to size. For example, bulk crystalline CdSe is a semiconductor with an optical band gap at 690 nm, and continuous optical absorption at shorter wavelengths. However, 3540/~ diameter CdSe crystallites containing some 1500 atoms exhibit a series of discrete excited states with a lowest excited state at 530 nm (1-3). With increasing size, these states shift red and merge to form the optical absorption of the bulk crystal. Electron microscopy and Bragg X-ray scattering measurements show that these crystallites have the same structure and unit cell as the bulk semiconductor. Such changes have now been observed in the spectra of many different semiconductors. This phenomenon is a "quantum size effect" related to the development of the band structure with increasing crystallite size (4). Smaller crystallites behave like large molecules (e.g. polycyclic aromatic hydrocarbons) their spectroscopic and photophysical properties. They are true "clusters" that do not exhibit bulk semiconductor electronic properties. In this review
1,012 citations
TL;DR: The eigenstates of electrons interacting in quantum dots in a magnetic field are studied and their effects on the magnetic-field dependence of the energy spectrum are illustrated with the calculations of the electronic heat capacity.
Abstract: The eigenstates of electrons interacting in quantum dots in a magnetic field are studied. The interaction has important effects on the magnetic-field dependence of the energy spectrum. However, when the confinement potential is quadratic, the optical excitation energies of the many-body system are exactly the same as those of a single electron. This makes the interaction effects difficult to observe directly but they could be seen by measuring the thermodynamic properties of the electrons. This is illustrated with the calculations of the electronic heat capacity.
759 citations
TL;DR: Current approaches for generating nanostructures of conducting materials are briefly reviewed, especially the use of three-dimensional crystalline superlattices as hosts for quantum-confined semiconductor atom arrays (such as quantum wires and dots) with controlled inter-quantum-structure tunneling.
Abstract: Nanoparticulate metals and semiconductors that have atomic arrangements at the interface of molecular clusters and "infinite" solid-state arrays of atoms have distinctive properties determined by the extent of confinement of highly delocalized valence electrons. At this interface, the total number of atoms and the geometrical disposition of each atom can be used to significantly modify the electronic and photonic response of the medium. In addition to teh novel inherent physical properties of the quantum-confined moieties, their "packaging" into nanocomposite bulk materials can be used to define the confinement surface states and environment, intercluster interactions, the quantum-confinement geometry, and the effective charge-carrier density of the bulk. Current approaches for generating nanostructures of conducting materials are briefly reviewed, especially the use of three-dimensional crystalline superlattices as hosts for quantum-confined semiconductor atom arrays (such as quantum wires and dots) with controlled inter-quantum-structure tunneling.
601 citations
TL;DR: The band-gap luminescence is not from the exciton state, but from a surface trapped state and results in long-lived bleach and induced-absorption features in pump-probe experiments.
Abstract: We use transient optical hole burning and photoluminescence to investigate the static and dynamic electronic properties of 32-\AA{} CdSe quantum dots. We observe a number of discrete electronic transitions, resolve LO-phonon progressions, and obtain homogeneous linewidths and electron--LO-phonon couplings. We find that the band-gap luminescence is not from the exciton state, but from a surface trapped state. Rapid (\ensuremath{\sim}160 fs) trapping into these surface states results in long-lived (\ensuremath{\sim}10--100 ns) bleach and induced-absorption features in pump-probe experiments.
509 citations
TL;DR: It is shown that the coupling strength is size independent when the typical dimensions of the electron charge distribution scale as the sphere radius, and the existence of surface modes is shown.
Abstract: We study electron-phonon coupling in the case of Fr\"ohlich or polar interaction, with special emphasis on the size dependence of the coupling strength for semiconductor nanospheres exhibiting quantum confinement of the carriers. We first derive the expression of the vibrational LO (longitudinal optic) and SO (surface optic) eigenfunctions for a sphere in the continuum approximation. After having quantized the vibrational eigenmodes, we give the electron-phonon interaction Hamiltonian. Using a model electronic charge distribution, we then show that the coupling strength is size independent when the typical dimensions of the electron charge distribution scale as the sphere radius. These theoretical considerations are then compared with experimental results obtained using resonant Raman scattering by CdSe-doped glasses with particles of various sizes. The experiments confirm the size independence of the coupling strength and also show the existence of surface modes.
452 citations
TL;DR: In this article, the authors describe a new synthetic approach to such colloids of CdS based on the competitive growth/termination of colloidal semiconductor species in the presence of thiophenol surfacecapping agents.
Abstract: Clusters of CdS in the quantum confinement regime C5O-A diameter are prepared in a rational technique whereby the cluster size and its distribution are controlled by chemical means. Competitive reaction chemistry between CdS core cluster growth and surface capping by thiophenolate leads to clusters whose core is essentially sphalerite CdS but whose reactive surface has been passivated by covalently attached phenyl groups. Adjustment of the sulfide to thiophenol ratio during synthesis takes advantage of the competitive reaction rates of these species with Cd ions to control the eventual cluster size. The clusters remain soluble in several organic solvents but may be isolated as stable powders and subsequently redissolved. The Cd "'NMR data for this series of capped clusters confirm the presence of sphalerite CdS as the cluster core and the increasing percentage of Cd involved in this core as the S/SPh ratio increases. Optical properties demonstrate well-behaved absorption edge and emission band shifts with development of exciton features as the clusters grow. Colloidal semiconductor species are currently under intense investigation as examples of nonmolecular materials that dem- onstrate the effects of quantum confinement.' The enhanced photoreactivity and photocatalysis as well as the predicted effects on nonlinear optical properties of these species has led to a wide range of synthetic approaches to these materials.* The key to any synthetic investigation of this sort must be the careful control of semiconductor cluster size and, even more important, the control of the size distribution. The relatively amorphous character of small clusters prepared in this way necessitates the use of structural probes that provide information even in the absence of long-range periodicity. While X-ra diffraction can offer information for particles in excess of 25 in crystalline dimensions, smaller particles are X-ray amorphous and larger sizes (>lo0 A) can suffer from significant contributions to the line widths by strain broadening. Quantitative interpretation using X-ray diffraction alone is therefore difficult. Among the various techniques suitable for such problems, solid- state NMR has the distinct advantage of providing element-se- lective, inherently quantitative information about local coordination environments and symmetries. In addition, NMR chemical shifts are also expected to be sensitive to cluster sizes, since the size quantization effects present in small semiconductor clusters should lead to an increase in the average excitation energy parameter in the paramagnetic term of Ramsey's chemical shift theory. This has been recently verified by Duncan and co-workers in a liq- uid-state "Se NMR study of colloidal CdSe sol~tion.~ We wish to describe a new synthetic approach to such colloids of CdS based on the competitive growth/termination of CdS species in the presence of thiophenol surface-capping agents. The reports by Steigerwald et aL4 using a micellar approach to ben- zeneselenol-capped CdSe clusters and by Dance et aLs on the preparation of a molecular fragment of sphalerite CdS where a Cdl& core was capped by 16 SPh groups led us to investigate this approach to the rational control of CdS cluster size by capping of the cluster surface by thiophenol-like species. Systematic, detailed optical and NMR behaviors have been revealed. Our NMR data, in addition, complement previous wide-line NMR studies undertaken on bulk cadmium sulfideb6 and add to the extremely limited database presently available for non-oxide chalcogenide systems.
409 citations
TL;DR: Self-consistent numerical solutions of the Poisson and Schrodinger equations have been obtained for electron states in a GaAs/Al heterostructure with confinement in all three spatial dimensions, indicating that the confining potential has nearly circular symmetry despite the square geometry of the gate, that the energy levels are quite insensitive to the charge in the quantum dot at a fixed gate voltage, and that the evolution of levels with increasing magnetic field is similar to that found for a parabolic potential.
Abstract: Self-consistent numerical solutions of the Poisson and Schr\"odinger equations have been obtained for electron states in a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructure with confinement in all three spatial dimensions. The equations are solved in the Hartree approximation, omitting exchange and correlation effects. Potential profiles, energy levels, and the charge in the quantum dot are obtained as functions of the applied gate voltage and magnetic field. First, the zero-magnetic-field case is considered, and the quantum-dot charge is allowed to vary continuously as the gate voltage is swept. Then, in connection with the phenomenon of Coulomb blockade, the number of electrons in the quantum dot is constrained to integer values. Finally, the calculation is extended to examine the evolution of levels in a magnetic field applied perpendicular to the heterojunction. Our results indicate that the confining potential has nearly circular symmetry despite the square geometry of the gate, that the energy levels are quite insensitive to the charge in the quantum dot at a fixed gate voltage, and that the evolution of levels with increasing magnetic field is similar to that found for a parabolic potential.
317 citations
TL;DR: Very small quantum-dot structures containing 210 to 25 electrons per dot have been prepared starting from modulation-doped AlGaAs/GaAs heterostructures, induced by nonlocal interaction which becomes important at small dimensions.
Abstract: Very small quantum-dot structures containing 210 to 25 electrons per dot have been prepared starting from modulation-doped AlGaAs/GaAs heterostructures. The far-infrared response consists of a set of resonances which split, in a magnetic field B, into branches with negative and positive B dispersion. The intersection of these resonances, in classical analogy edge magnetoplasmons, leads to an anticrossing of the dispersions. This resonant coupling is induced by nonlocal interaction which becomes important at small dimensions.
288 citations
TL;DR: In this article, the authors presented the first documented preparation of relatively monodisperse, redissolvable, crystalline, nanometer-size particles of GaAs, using a reaction developed by Wells and co-workers.
Abstract: The optical spectra of semiconductor crystallites whose dimension is comparable to the bulk exciton diameter show quantum confinement effects. To date, experimental studies of nanometer-size crystallites have been restricted to II-VI and I-VII semiconductors, while III-V semiconductors, including one of the most important direct band gap semiconductors, GaAs, have not yet been studied in this form, because of the numerous difficulties encountered in their preparation. Compared to the I-VII and II-VI semiconductors, the III-Vs have a greater degree of covalent bonding, a less ionic lattice, and larger exciton diameters (the exciton diameter in GaAs is 190 {angstrom}, compared to 60 {angstrom} for CdS). For this reason, quantum size effects on the optical spectra have been predicted to be more pronounced in the III-V class of materials than in the II-VIs, and crystallites of GaAs are more likely to find application in optical devices than CdS clusters. In this paper the authors present the first documented preparation of relatively monodisperse, redissolvable, crystalline, nanometer-size particles of GaAs. The nanocrystals were prepared in polar organic solvents, using a reaction developed by Wells and co-workers. GaCl{sub 3} and As(SiMe{sub 3}){sub 3} react in hydrocarbons to give solid products, which on heating afford GaAs. Theirmore » X-ray diffraction experiments on the black GaAs powder prepared in this manner show that the domain size is 100 {angstrom}. They carried out the same reaction in quinoline.« less
266 citations
TL;DR: In this paper, a new formalism for determining energy eigenstates of spherical quantum dots and cylindrical quantum wires in the multiple-band envelope function approximation is described, based upon a reformulation of the K⋅P theory in a basis of eigen states of total angular momentum.
Abstract: We describe a new formalism for determining energy eigenstates of spherical quantum dots and cylindrical quantum wires in the multiple-band envelope-function approximation. The technique is based upon a reformulation of the K⋅P theory in a basis of eigenstates of total angular momentum. Stationary states are formed by mixing bulk energy eigenvectors and imposing matching conditions across the heterostructure interface, yielding dispersion relations for eigenenergies in quantum wires and quantum dots. The bound states are studied for the conduction band and the coupled light and heavy holes as a function of radius for the GaAs/AlxGa1-xAs quantum dot. Conduction-band–valence-band coupling is shown to be critical in a "type-II" InAs/GaSb quantum dot, which is studied here for the first time. Quantum-wire valence-subband dispersion and effective masses are determined for GaAs/AlxGa1-xAs wires of several radii. The masses are found to be independent of wire radius in an infinite-well model, but strongly dependent on wire radius for a finite well, in which the effective mass of the highest-energy valence subband is as low as 0.16m0. Implications of the band-coupling effects on optical matrix elements in quantum wires and dots are discussed.
TL;DR: The optical properties of the quantum dots are computed, and it is shown that the Coulomb interaction significantly influences the allowed dipole transitions, causing increasing two-pair absorption on the high-energy side of the decreasing one- Pair absorption.
Abstract: The influence of the Coulomb interaction on one and two electron-hole-pair excitations in semiconductor quantum dots is analyzed. Using a numerical matrix-diagonalization scheme, the energy eigenvalues and the eigenfunctions of the relevant states are computed. Significant deviations from the strong-confinement approximation are observed. It is shown that the biexciton binding energy increases with decreasing dot size. This result is verified using third-order perturbation theory for small quantum dots. The optical properties of the quantum dots are computed, and it is shown that the Coulomb interaction significantly influences the allowed dipole transitions, causing increasing two-pair absorption on the high-energy side of the decreasing one-pair absorption. Surface-polarization effects are studied for quantum dots embedded in another dielectric medium.
TL;DR: Theoretical and experimental results are reported which provide the first evidence for biexciton states in semiconductor quantum dots, observed as pronounced induced absorption features on the high-energy side of the bleached exciton resonances in femtosecond and nanosecond pump-probe experiments of quantum dots in glass matrices.
Abstract: Theoretical and experimental results are reported which provide the first evidence for biexciton states in semiconductor quantum dots. The theory predicts an increasing biexciton binding energy with decreasing dot size. Unlike bulk semiconductors, quantum dots have excited biexciton states which are stable. These biexciton states are observed as pronounced induced absorption features on the high-energy side of the bleached exciton resonances in femtosecond and nanosecond pump-probe experiments of quantum dots in glass matrices.
TL;DR: With far-infrared spectroscopy, coupling between electron quantum dots becomes visible in the electronic excitation spectrum and gated GaAs-AlGaAs quantum wells that enable field-effect tuning of the coupling between adjacent dots are employed.
Abstract: With far-infrared spectroscopy, coupling between electron quantum dots becomes visible in the electronic excitation spectrum. We employ gated GaAs-AlGaAs quantum wells that enable field-effect tuning of the coupling between adjacent dots. For noninteracting quantum dots in a magnetic field we observe the characteristic edge- and bulk-mode spectrum.. The coupling of dots is reflected by a branching of the bulk mode into a cyclotron-resonance-like and a magnetoplasmonlike mode and a splitting of the edge mode. The latter is caused by formation of new edge orbits embracing two adjacent dots.
TL;DR: A simple model demonstrates that the oscillations arise from the formation of a miniband structure in the periodic crystal, including energy gaps and minibands which contain fifteen discrete states.
Abstract: We have studied the magnetotransport properties of an artificial one-dimensional crystal. The crystal consists of a sequence of fifteen quantum dots, defined in the two-dimensional electron gas of a GaAs/AlGaAs heterostructure by means of a split-gate technique. At a fixed magnetic field of 2 T, two types of oscillations with different amplitude and period are observed in the conductance as a function of gate voltage. A simple model demonstrates that the oscillations arise from the formation of a miniband structure in the periodic crystal, including energy gaps and minibands which contain fifteen discrete states.
TL;DR: On montre que la position des raies de resonance dans le spectre d'absorption magneto-optique d'un point quantique a potentiel de confinement parabolique asymetrique est independante de l'interaction electron-electron et du nombre d’electrons du point quantiques, dans l’approximation de the masse effective.
Abstract: We show that the position of the resonance lines in the magneto-optical absorption spectrum of a quantum dot with a (asymmetric) parabolic confinement potential is independent of the electron-electron interaction and the number of electrons in the quantum dot.
TL;DR: The observation of quantum beats in the decay of the coherent polarization of intrinsic excitations in GaAs/GaAlAs quantum wells is reported, which arises from interference of excitons with slightly different quantum confinement energy due to well-width fluctuations.
Abstract: We report the observation of quantum beats in the decay of the coherent polarization of intrinsic excitations in GaAs/GaAlAs quantum wells. The beating arises from interference of excitons with slightly different quantum confinement energy due to well width fluctuations.
TL;DR: In this article, the authors analyzed the entire precipitation process in terms of several decomposition stages: nucleation, normal growth, coalescence of quantum dots, and devitrification of the glass matrix itself.
Abstract: The sequence of stages during precipitation of semiconductor (e.g., CdS, CdSe) clusters from supersaturated glasses exhibiting quantum‐confinement effects was investigated. The rate of formation of nanometer‐size ‘‘quantum dots’’ distributed in a continuous glass matrix is critically determined by the time and temperature of the heat treatment given to the quenched glasses. The entire precipitation process was analyzed in terms of several decomposition stages: nucleation, normal growth, coalescence of quantum dots, and devitrification of the glass matrix itself. Experimental data obtained by differential thermal analysis were utilized to identify the heat‐treatment temperature range associated with the precipitation stages. The size distribution of CdSe quantum‐dot clusters was analyzed using our transmission electron microscopy data. The data of Ekimov et al. [Solid State Commun. 56, 921 (1975)] was reduced to time‐temperature master plots useful for precipitating quantum dots of a given size in glasses.
TL;DR: In this article, Raman measurements were carried out on Ge quantum dots from 6.1 to 15 nm in size embedded in SiO2 thin films, and the samples were prepared by rf co-sputtering and post-annealing.
Abstract: Raman measurements were carried out on Ge quantum dots from 6.1 to 15 nm in size embedded in SiO2 thin films. The samples were prepared by rf co‐sputtering and post‐ annealing. In contrast to the amorphous‐like broad spectra previously obtained for gas‐ evaporated Ge microcrystals of comparable sizes, relatively sharp lines around 300 cm−1 were observed, because the present dots satisfy the fixed boundary condition. The increase in the linewidth observed with decreasing the size is in good agreement with the results of the calculation based on the phonon confinement model. However, the downward shift of the line predicted from the calculation was not observed presumably due to the compressive stress exerted on the dots.
01 Jan 1990
TL;DR: In this paper, a revised second edition on the "Quantum Theory of the Optical and Electronic Properties of Semiconductors" presents the basic elements needed to understand and engage in research in semiconductor physics.
Abstract: This revised second edition on the "Quantum Theory of the Optical and Electronic Properties of Semiconductors" presents the basic elements needed to understand and engage in research in semiconductor physics. In this revised second edition misprints are corrected and some new and more detailed material is added. In order to treat the valence-band structure of semiconductors, an introduction to the k.p. theory and the related description in terms of the Luttinger Hamiltonian is included. An introductory chapter on mesoscopic semiconductor structures discussing the modifications of the envelope function approximation caused by the spatial quantum confinement is also included. Many results are developed in parallel first for bulk material, and then for quasi-two-dimensional quantum wells, and for quasi-one-dimensional quantum wires. Semiconductor quantum dots are treated in a separate chapter. The discussion of time-dependent and coherent phenomena in semiconductors has been considerably extended by including a section dealing with the theoretical description of photon echoes in semiconductors. A new chapter on magneto-absorption has been added, in which magneto-excitons and magneto-plasmas in two-dimensional systems are discussed. The chapter on electron kinetics due to the interaction with longitudinal-optical phonons has been extended. The material is presented in sufficient detail for graduate students and researchers who have a general background in quantum mechanics, and is aimed at solid state physicists, engineers, materials and optical scientists.
TL;DR: In this paper, the energy levels of electrons confined to a circular quantum well with hard walls are calculated in the presence of a perpendicular magnetic field and compared with the case of soft-wall confinement (parabolic potential).
Abstract: The energy levels of electrons confined to a circular quantum well with hard walls are calculated in the presence of a perpendicular magnetic field. The results are compared with the case of soft‐wall confinement (parabolic potential). There are important differences in the transition energies of the magneto‐optical spectrum: (i) in contrast to the parabolic case where only two transition energies are found, in the hard‐wall case there are many transitions possible which have different energies. Only a small number of them however have sufficient oscillator strength to be observable; (ii) with increasing magnetic field the energies approach the two‐dimensional results much faster than for the soft‐wall case. In quantum dots with many electrons we calculate the Fermi energy as a function of the magnetic field.
TL;DR: In this article, five discrete excitonic transitions were observed in quantum dots, i.e. quantum-sized CdS, as a function of particle size, and the experimentally determined energy levels of the states were compared to eigenvalues calculated from products of two particle-in-a-box s or p orbitals.
TL;DR: The energies of the two energetically lowest dipole-allowed electron-hole-pair states in semiconductor microcrystallites are computed variationally and significant deviations from the infinite-potential approximation are obtained.
Abstract: The energies of the two energetically lowest dipole-allowed electron-hole-pair states in semiconductor microcrystallites are computed variationally. Details of the quantum confinement conditions, such as the finite value of the quantum confinement potential and the different effective electron-hole masses inside and outside the crystallites, are considered explicitly. Significant deviations from the infinite-potential approximation are obtained.
TL;DR: Le spectre d'absorption lineaire de ces microcristallites presente six pics de confinement quantique, on distingue plusieurs mecanismes de non linearite optique.
Abstract: Microcrystallites of CdTe were grown in a special-formula glass, yielding CdTe dots; the linear-absorption spectrum exhibits as many as six quantum-confinement peaks. Excitation of the sample with pulses ranging from femtoseconds to microseconds has allowed us to distinguish between various mechanisms for optical nonlinearity. At very early times, phase-space filling and Coulomb interaction between the excited charged carriers is responsible for the absorption changes, \ensuremath{\delta}\ensuremath{\alpha}. At later times, Coulomb effects due to trapped carriers remain and last for nanoseconds or microseconds.
TL;DR: In this paper, a theory for the one and two-pair states in quantum dots is developed that fully includes the relevant Coulomb interactions, and results are presented for intrinsic quantum dots and for quantum dots with impurities.
Abstract: Quantum-confinement effects in CdSe microcrystallites in a glass matrix are investigated in the nanosecond time domain. The results of pump–probe and single-beam absorption saturation measurements show strong evidence for electron–hole quantization in the semiconductor microstructures, a different bleaching behavior from those of bulk semiconductors and multiple quantum wells, and a trend of increased saturation intensity with decreased microcrystallite size. A theory for the one- and two-pair states in quantum dots is developed that fully includes the relevant Coulomb interactions. The theory is evaluated numerically, and results are presented for intrinsic quantum dots and for quantum dots with impurities. The experimentally observed nonlinearities are attributed to saturation of one-electron–hole-pair resonances and induced absorption caused by two-pair resonances in the presence or absence of impurities (traps).
TL;DR: Calcul des effets de polarons pour des electrons confines dans des fils quantiques lateraux monodimensionnels et des points quantiques paraboliques en prenant en compte a la fois l'interaction electron-phonon LO volumique et electron- phonon d'interface.
Abstract: Calcul des effets de polarons pour des electrons confines dans des fils quantiques lateraux monodimensionnels et des points quantiques paraboliques, en prenant en compte a la fois l'interaction electron-phonon LO volumique et electron-phonon d'interface
TL;DR: Employing electrostatic confinement with a dual-gate device, periodic arrays of electron dots on Si widely tunable in diameter and electron number are realized, indicating a direct effect of strong quantum confinement.
Abstract: Employing electrostatic confinement with a dual-gate device we realize periodic arrays of electron dots on Si widely tunable in diameter and electron number. From far-infrared transmission studies of dimensional resonances, we deduce dot diameters down to 40 nm for as little as 20 electrons in quantum states spaced by more than 5 meV. Excitation energies as well as mode dispersions in finite magnetic fields are found to strongly depend on the strength and the shape of the lateral confining potential. A detailed analysis of the oscillator strengths indicates a direct effect of strong quantum confinement.
TL;DR: In this article, the enhancement of optical nonlinearity due to quantum confinement in semiconductor-doped glasses was discussed, in which the enhancement was due to a decrease in the spectral width rather than in an increase of matrix elements.
Abstract: We first discuss theoretically the enhancement of the optical nonlinearity due to quantum confinement in semiconductor-doped glasses. This quantum confinement mediated enhancement also pertains to the figure of merit x (3)/α, in which case it is due to a decrease in the spectral width rather than in an increase of the matrix elements. We then report on frequency and size-dependent measurements which confirm the theoretically expected enhancement due to quantum confinement.
TL;DR: In this paper, the spatial resolution of the capacitance-voltage profiling technique on semiconductors with one-dimensional quantum confinement is given by the spatial extent of the wave function, and it is shown that the saturation of the free-carrier density of highly Si δ-doped GaAs grown by molecular beam epitaxy is due to inactive Si impurities.
Abstract: The spatial resolution of the capacitance‐voltage profiling technique on semiconductors with one‐dimensional quantum confinement is shown to be given by the spatial extent of the wave function. The Debye length limitation does not apply. Capacitance‐voltage profiles on δ‐doped GaAs of density 4–4.5×1012 cm−2 exhibit widths of 20 and 48 A for p‐ and n‐type impurities, respectively. The profiles agree with the theoretical resolution function and with Be and Si profiles measured by secondary‐ion mass spectroscopy. It is further shown that the saturation of the free‐carrier density of highly Si δ‐doped GaAs grown by molecular beam epitaxy is due to inactive Si impurities
TL;DR: In this article, linear absorption and excitation dependent luminescence measurements on CdSSe quantum dots in glass are reported, and the new aspects of the spectra are: (i) Stokes shift of linear emission versus absorption and (ii) appearance of new structures in the high energy wing of the luminecence peak under high excitation, which are interpreted as consequences of Coloumb effects.
Abstract: Linear absorption and excitation dependent luminescence measurements on CdSSe quantum dots in glass are reported. The new aspects of the spectra are: (i) Stokes shift of linear emission versus absorption and (ii) appearance of new structures in the high energy wing of the luminescence peak under high excitation, which are interpreted as consequences of Coloumb effects, important for dot radii around the exciton Bohr radius.