scispace - formally typeset
Search or ask a question

Showing papers on "Quantum dot published in 1987"


Journal ArticleDOI
TL;DR: In this article, the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)] were analyzed theoretically, and the phonon broadening of these lines was considered.
Abstract: We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.

843 citations


Journal ArticleDOI
TL;DR: In this article, the optical properties of glasses containing a small amount of thermally developed CdSexS1−x microcrystalline phase are studied with emphasis on quantum confinement effects exhibited at small crystallite size.
Abstract: The optical properties of glasses containing a small amount of thermally developed CdSexS1−x microcrystalline phase are studied with emphasis on quantum confinement effects exhibited at small crystallite size. Optical absorption, photoluminescence, x‐ray diffraction, and transmission electron microscopy are used to examine microcrystallites as a function of composition and development. Results are presented for a series of commercially available CorningR filter glasses with a selenium mole fraction in the range 0.28≤x≤0.74, as well as for several experimental glasses in which the average microcrystallite diameters range from 30 to 80 A. Optical effects observed in the experimental glasses that are due to electron and hole confinement are not present in the filter glasses considered; variations in optical properties of the filters are due to changes in stoichiometry of the CdSexS1−x mixed anion system. A brief discussion of other microcrystalline phases in glass is also presented. These microcrystallites show room‐temperature optical absorption structure analogous to bulk crystal excitons; the temperature dependence of this structure is contrasted with that resulting from quantum confinement in CdSexS1−x glasses.

564 citations


Journal ArticleDOI
TL;DR: In this article, two salient features of the excitonic state in semiconductor quantum dots are theoretically clarified, and a comprehensive interpretation is presented for the fast and slow-decay components in phase conjugation and luminescence measurements.
Abstract: Two salient features of the excitonic state in semiconductor quantum dots are theoretically clarified. One is the enhanced excitonic optical nonlinearity arising from the state filling of discrete levels due to the quantum size effect. The calculated third-order nonlinear susceptibility explains successfully the recent experimental results. The other feature is the exciton dynamics in semiconductor quantum dots. A comprehensive interpretation is presented for the fast- and slow-decay components in phase conjugation and luminescence measurements.

242 citations


Journal ArticleDOI
TL;DR: In this article, the interband optical absorption of a nonuniform semiconductor quantum dot system is calculated and the effect of dot size variation on the resolvability of the absorption peaks is estimated.
Abstract: The interband optical absorption of a nonuniform semiconductor quantum dot system is calculated. The effect of dot size variation on the resolvability of the absorption peaks is estimated. The dots are assumed to be cubic, with a size distribution described by a Gaussian function. It is shown that the total absorption spectrum of such a dot system depends strongly on the dot size distribution described by the parameter ξ, the ratio of the standard deviation of the dot size to the average dot size of the system. The range of ξ values for which the absorption peaks are resolvable is given.

122 citations


Journal ArticleDOI
TL;DR: In this paper, a sheet of donor atoms is incorporated in (100) Si during molecular beam epitaxial growth, and the width of such δ−function doping layers is only a few lattice planes.
Abstract: We present a procedure whereby a sheet of donor atoms is incorporated in (100) Si during molecular beam epitaxial growth. Analysis by secondary ion mass spectroscopy and transmission electron microscopy shows that the width of such δ‐function doping layers is only a few lattice planes. Tunneling spectroscopy and transport measurements give evidence for quantum confinement of the electronic charge in the layer and thus confirm the narrow width.

101 citations


Journal ArticleDOI
TL;DR: In this paper, a photoluminescence study of ZnSe−ZnSxSe1−x strained layer superlattices with x=0.19 grown by molecular beam epitaxy is presented.
Abstract: A photoluminescence study of ZnSe‐ZnSxSe1−x strained‐layer superlattices with x=0.19 grown by molecular beam epitaxy is presented. We observe clear shifts of the excitons to higher energies as the well widths are reduced. These shifts are interpreted in terms of quantum confinement effects using the envelope function approach and the strain‐induced effects using the deformation potential theory. From our analysis we conclude that most of the band offsets between ZnSe‐ZnSxSe1−x are taken up by the valence bands.

29 citations


Journal ArticleDOI
TL;DR: In this paper, a method of measuring the random motion of charge carriers perpendicular to the plane of the quantum confinement is demonstrated, with sub-angstrom resolution, to determine the mean fluctuation of the average perpendicular position of the electron wave function during transport parallel to the potential barrier.
Abstract: Drawing upon our current understanding of the weak localization correction to the Drude conductivity in quasi‐two‐dimensional systems, a method of measuring the random motion of charge carriers perpendicular to the plane of the quantum confinement is demonstrated. This technique has been applied to silicon inversion layers and a GaAs heterojunction to determine, with subangstrom resolution, the mean fluctuation of the average perpendicular position of the electron wave function during transport parallel to the potential barrier.

12 citations


Journal ArticleDOI
TL;DR: In this article, the optical absorption coefficient in ultrathin (∼10 A) hydrogenated amorphous germanium (a•Ge:H) layers was determined by in situ reflectivity measurements.
Abstract: The optical absorption coefficient in ultrathin (∼10 A) hydrogenated amorphous germanium (a‐Ge:H) layers deposited on hydrogenated amorphous silicon layers was determined by in situ reflectivity measurements. The decrease in the absorption coefficient in the ultrathin a‐Ge:H layers, compared to that of thick films, is explained by an upward shift in the conduction band edge due to quantum confinement of electrons with effective mass of 0.4m0.

9 citations


Journal ArticleDOI
01 Oct 1987
TL;DR: In this paper, the authors present the linear and nonlinear optical properties seen in III-V (GaInAs/InP) multi-quantum well structures and demonstrate the nonlinear properties associated to the absorption saturation of the heavy hole excitons.
Abstract: Semiconductor quantum wells and their band gap resonant nonlinear optical properties have been shown to be important because of their potential for applications in optical switching and signal processing. The near band gap optical properties of quantum well structures are dominated by strong excitonic effects due to quantum confinement. There is much interest in the use of optical devices as MQW for performing all optical switching or by using electrostatic field to change the absorption directly by driving electrons in the QW structure. Such effects are able to produce a family of optical logic elements. In this paper, we present the linear and nonlinear optical properties seen in III-V (GaInAs/InP) multi quantum well structures. The nonlinear properties associated to the absorption saturation of the heavy hole excitons are demonstrated. We review the applications of these nonlinear processes in the field of the 2D and integrated optics (intrinsic bistability and nonlinear coupler) Etude des caracteristiques de transmission optique et mise en evidence d'effets non lineaires associes a la saturation d'absorption excitonique; applications (bistabilite intrinseque, coupleur optique)

7 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the quantum confinement effects in GaAs/AlAs multiple quantum well heterostructures with varying barrier-layer thicknesses down to 1.3 nm for two sets of samples with the nominal well widths of 9.2 and 6.4 nm.
Abstract: Excitonic resonance structures in GaAs/AlAs multiple quantum well heterostructures with varying barrier-layer thicknessesL B down to 1.3 nm are investigated for two sets of samples with the nominal well widths ofL Z =9.2 and 6.4 nm, by 2K photoluminescence excitation spectroscopy. The observed resonance energies of then=1 heavyhole (1 hh) and light-hole (1 lh) free excitons imply that quantum confinement effects persist at least down to the decreased barrier-layer thickness ofL B =1.3 nm. This result is inconsistent with the red shifts expected from the simple well-coupling theory within the one-band Kronig-Penney model at theГ point. Instead, blue shifts of 6–8 meV (8–17 meV) are observed for the 1 hh (1 lh) excitonic resonance peaks whenL B is decreased from 10 to 2 nm. A relative decrease of the oscillator strength of the 1 lh transition compared to the 1 hh transition is also observed asL B is decreased. These results manifest important effects of the indirect-gap barrier material for the actual wavefunction matching across the interface and the breakdown of the envelope function approach to GaAs/AlAs quantum well heterostructures with ultrathin barriers.

4 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of quantum confinement and of a superlattice in the under confinement layer on interface recombination was studied in MBE grown GaAs-Ga1−xAlxAs undoped double heterostructures with GaAs thicknesses varying between 15 A and 1 µm.
Abstract: Interface recombination has been studied in MBE grown GaAs-Ga1−xAlxAs undoped double heterostructures with GaAs thicknesses varying between 15 A and 1 µm. We study the influence of quantum confinement and of a superlattice in the under confinement layer on interface recombination. We also show that radiative recombination at room temperature in quantum wells is bimolecular.

Book ChapterDOI
01 Jan 1987
TL;DR: In this paper, the authors consider the problem of the band offset between two materials, i.e., the fraction of the energy difference between the two materials which is taken by the valence band edge.
Abstract: The design of new microelectronics or optoelectronics devices often involves semiconductor heterolayers which are thin enough to allow pronounced quantum size effects. The latter are due to the confinement of electrons, holes or excitons within one layer with little penetration into the other layers. To achieve such a confinement it is necessary that potential energy steps exist between the heterolayers in order to prevent the leakage of the carrier wave function outside the slab where it is essentially localized. Thus, behind quantum confinement there is the idea that at the interfaces the conduction and valence band edges change rapidly over a Small distance. One of the central questions of heterolayer physics is thus the magnitude of the fraction of the band-gap energy difference between two materials which is taken by, say, the valence band edge, i.e. the question of the band offset.

Journal ArticleDOI
TL;DR: In this paper, the operating conditions for successful e-beam lithography for the fabrication of gratings for first-order distributed feedback (DFB) semiconductor lasers operating at wavelengths from 0.85μm to 1.55μm have been investigated.

Journal ArticleDOI
L. Yang1, B. Abeles1
TL;DR: In this paper, the optical absorption coefficient in ultra thin (∼10A) a-Ge:H layers deposited on a-Si:H layer was determined by in-situ reflectivity measurements.
Abstract: The optical absorption coefficient in ultra thin (∼10A) a-Ge:H layers deposited on a-Si:H layers, was determined by in-situ reflectivity measurements. The decrease in the absorption coefficient in the ultra thin a-Ge:H layers, compared to that of thick films, is explained by an upward shift in the conduction band edge due to quantum confinement of electrons with effective mass of 0.4 m o .