Showing papers on "Potential well published in 2000"
TL;DR: In this article, a photoluminescence study of silicon nanoclusters produced by laser ablation was conducted and it was found that by varying the preparation parameters it was possible to change the mean cluster size in the range 1-5 nm.
Abstract: We report a photoluminescence study of silicon nanoclusters produced by laser ablation. It was found that by varying the preparation parameters it was possible to change the mean cluster size in the range 1–5 nm. Within this size variation, the photoluminescence band shifts in a wide spectral region from near ultraviolet to near infrared. This size-dependent photoluminescence of Si nanoclusters is consistent with a quantum confinement effect. The observed influence of cluster oxidation on the luminescence properties also supports the quantum confinement interpretation. We proposed a discrete size model which supposes that the spectral position of the luminescence band is essentially determined by the volume of clusters with a complete outer atomic layer. In the framework of this model, we were able to deconvolute the observed luminescence bands into a set of fixed Gaussian bands. The model is supported by the observation of a size selective doping of Si nanoclusters whose effect was well explained by Auger recombination. Finally, our model allowed us to obtain a dependence of the optical gap on the cluster size which is in good agreement with existing calculations of Si nanocrystal electronic structure.
211 citations
TL;DR: In this paper, the authors studied the use of the effective potential in a triangular well formed between the oxide and the depletion field of the semiconductor, and determined the quantization energy of the carriers in the potential well and their mean set-back from the interface.
47 citations
TL;DR: In this article, the nonlinear optical properties of Fe2O3 nanoparticles were investigated by the signal-beam Z-scan technique with Ar+ and Ne-He lasers, and the largest reported effective nonlinear coefficient, n 2 =−8.07×10 −7 cm 2 / W, was obtained.
Abstract: Nonlinear optical properties of Fe2O3 nanoparticles were investigated by the signal-beam Z-scan technique with Ar+ and Ne–He lasers. The largest reported effective nonlinear coefficient, n 2 =−8.07×10 −7 cm 2 / W , was obtained. It is demonstrated that the nonlinear optical response originals from quantum confinement effect.
47 citations
TL;DR: In this article, the photoluminescence properties of GaSe and Si nanowires were investigated in correlation with the diameter of the crystalline core of the GaSe core.
Abstract: GaSe and Si nanowires (SiNWs) were synthesized by physical evaporation. The photoluminescence (PL) properties of the Si nanowires were investigated in correlation with the diameter of the crystalline core. Intensive light emission was observed peaking at dark red, green and blue regions for the as grown and partially oxidized SiNW samples. The red PL emission is ascribed to the quantum confinement effect of the crystalline core of the SiNWs, while the green and blue ones are attributed to the radiative recombination of the defect centers in the amorphous silicon oxide layer surrounding the SiNWs.
43 citations
TL;DR: In this paper, a GaInAsP/InP multiple-layered quantum-wire laser with the wire width of 21 nm in the period of 100 nm was realized by CH4/H2 reactive-ion etching followed by slight wet chemical etching and embedding growth by organometallic vapor phase epitaxy.
Abstract: GaInAsP/InP multiple-layered quantum-wire lasers with the wire width of 21 nm in the period of 100 nm were realized by CH4/H2 reactive-ion etching followed by slight wet chemical etching and embedding growth by organometallic vapor phase epitaxy. A threshold current density as low as 1.45 kA/cm2 was obtained with the cavity length of 980 µm. To our knowledge, this is the lowest value reported for 1.55 µm GaInAsP/InP quantum-wire lasers fabricated by the etching and regrowth method. Because of the temperature dependence of the lasing wavelength, a relatively large blue shift of 47 meV in the quantum-wire laser was observed, which can be attributed to not only a lateral quantum confinement effect but also a three-dimensional compressive strain effect. Finally, we improved the initial wafer structure in order to suppress over-etching of the active region, and obtained lasers consisting of a five-layered wirelike active region with good size uniformity (wire width of 42 nm, period of 120 nm). A threshold current density as low as 540 A/cm2 was obtained with the cavity length of 1.38 mm.
33 citations
TL;DR: In this paper, optical properties of quantum dots and quantum wires of diluted magnetic semiconductors were investigated and the Zeeman shift of the exciton luminescence was observed with an effective g value of 91.
Abstract: We report optical properties of quantum dots and quantum wires of diluted magnetic semiconductors. The quantum dots of Cd1−xMnxSe (x=0.03) show the exciton luminescence at around 2.4 eV, which indicates a strong confinement effect of the exciton energy corresponding to the dot size of 4–6 nm. The Zeeman shift of the exciton luminescence was observed with an effective g value of 91, showing a significant exchange interaction of the excitons with the Mn ions in the dots. The exciton luminescence from the quantum wires of Cd1−xMnxSe (x=0.08) shifts by 5.2 meV to the higher energy side with decreasing the wire width from 126 to 26 nm. The high energy shift in the narrow wires indicates the influence of the one-dimensional quantum confinement effect for the exciton states. The effective g value of the exciton in these quantum wires is 100–150. The exciton luminescence from the wires is linearly polarized (up to 80%) parallel to the wire direction at zero field, which indicates one-dimensional properties of the...
31 citations
TL;DR: In this paper, a few-body physics method was applied to calculate the low-lying states of the exciton of a GaAs disk-like quantum dot with a parabolic potential.
Abstract: The method of few-body physics is applied to calculate the low-lying states of the exciton of a GaAs disk-like quantum dot with a parabolic potential. The binding energy of the exciton in quantum disks is calculated for two different thickness as a function of the quantum-disk radius. The four lowest exciton levels on dependence of the disk thickness is investigated.
27 citations
TL;DR: In this paper, a single-electron transistor based on undoped Si nanocrystals having radii of approximately 3 nm was fabricated and the carrier transport properties observed experimentally have been well understood in terms of carrier tunneling and Coulomb blockade effects.
27 citations
TL;DR: In this paper, two emission bands were simultaneously observed in iron-passivated porous silicon and their peak energies were in good agreement with the first two gap energies calculated for silicon nanocrystallites.
Abstract: Two emission bands were simultaneously observed in iron-passivated porous silicon and their peak energies were in good agreement with the first two gap energies calculated for silicon nanocrystallites $(nc\ensuremath{-}\mathrm{Si}).$ This result indicates the existence of separate conduction subbands caused by the quantum confinement of carriers in $nc\ensuremath{-}\mathrm{Si}.$ It was also found that under the frame of the quantum confinement effect, the distribution of the photoluminescence intensity over emission wavelength could be well explained by the size distribution of $nc\ensuremath{-}\mathrm{Si}.$ These facts support the quantum confinement model of the luminescence in porous silicon.
25 citations
TL;DR: In this paper, an analytical description of the current conduction process in composite CdTe:TiO2 is discussed, and it is shown that tunnelling between the CdTE nanocrystals is not a dominant mechanism, as a three-dimensional network is not realized due to small thickness and lower coverage.
Abstract: CdTe nanocrystals sequestered and passivated in an amorphous TiO2 thin film matrix have been prepared by RF sputtering from a composite TiO2:CdTe target. The CdTe nanocrystal size and volume fraction increases from 15 to 40 nm and 2 to 20% respectively as the film thickness increases, typically from 0.05 to 0.25 µm. A systematic dependence of the optical band edge on the CdTe nanocrystal size shows a strong quantum confinement effect. The optical edge shifts are significantly higher than the theoretical prediction based on single-particle confinement of decoupled electrons and holes. This is understood on the basis of nucleation-controlled growth of CdTe nanocrystals by direct vapour phase condensation, in which small nuclei are rapidly passivated by TiO2 depositing at much higher rates. The nano-sized CdTe growth island thus formed comprises of several TiO2 passivated nanocrystals. Electrical conduction behaviour of these films show that tunnelling between the CdTe nanocrystals is not a dominant mechanism, as a three-dimensional network is not realized due to small thickness and lower coverage. The current transport is essentially space-charge-limited. The injection of electrons from nano-sized CdTe crystals follows spherical radial space charge flow which modifies the usual power law dependence from quadratic to 3/2. The analytical description of the current conduction process in composite CdTe:TiO2 is discussed.
25 citations
TL;DR: In this article, the optical absorption spectra of the heat treated particles dispersed on a glass substrate have been delineated and the absorption peak shows a maximum in wavelength as a function of heat treatment temperature.
Abstract: Ag2O particles of sizes varying from 6.0 to 16 nm have been prepared by a chemical method. These have been subjected to a heat treatment at temperatures varying from 533 to 623 K. The optical absorption spectra of the heat treated particles dispersed on a glass substrate have been delineated. The absorption peak shows a maximum in wavelength as a function of heat treatment temperature. This has been explained on the basis of formation of nanometer-sized silver layer on the Ag2O particles and the consequential electron confinement within the same.
TL;DR: In this paper, photoacoustic (PA), photoluminescence (PL), and atomic force microscopy (AFM) techniques were applied on porous silicon (PS) layers to study the influence of chemical etching by low-concentration hydrofluoric acid.
Abstract: We applied photoacoustic (PA), photoluminescence (PL), photoluminescence excitation (PLE), and atomic force microscopy (AFM) techniques on porous silicon (PS) layers to study the influence of chemical etching by low-concentration hydrofluoric acid. The chemical etching reveals the formation of PS layers of small dimensions by AFM observations, indicating the possibility of a strong quantum confinement effect. PA spectroscopy is useful to obtain the optical absorption characteristic for strongly scattering media such as PS and it helps to confirm the above speculation by indicating the blueshift of the fundamental absorption edge for the PS layer with chemical etching. PL spectroscopy also confirms the possibility of a quantum confinement effect by revealing the strong intensity and blueshift for the PS layer with chemical etching. PLE measurements suggest that the site for the radiative processes is different from that for the recombination of carriers and the PL of PS layers were dominated only by small ...
TL;DR: In this article, the modified droplet epitaxy method using sulfur termination was applied to fabricate InAs quantum dots on GaAs(001) substrates for the first time, and it was observed that the S-terminated surface effectively prevents the two-dimensional growth of InAs, forming InAs nanocrystals.
Abstract: We have applied the modified droplet epitaxy method using sulfur termination to fabricate InAs quantum dots on GaAs(001) substrates for the first time. It is observed that the S-terminated surface effectively prevents the two-dimensional growth of InAs, forming InAs nanocrystals. From the magneto-photoluminescence measurements of this structure, three-dimensional quantum confinement effect was confirmed. This modified droplet epitaxy method is promising for the fabrication of quantum dots, not only in the lattice-matched system but also in the lattice-mismatched system.
TL;DR: In this paper, a new method for the preparation of semiconductor PbS quantum dot-doped Ormocer (Organically Modified Ceramic) has been developed.
Abstract: A new method for the preparation of semiconductor PbS quantum dot-doped Ormocer (Organically Modified Ceramic) has been developed. The Ormocer matrix was prepared through the hydrolysis and condensation of alkoxysilane precursors (sol-gel process). Formation of PbS particles took place in the porous Ormocer through H2S gas reaction with a lead precursor incorporated at the solution stage. Control of the PbS dot size was achieved through the use of organically substituted trifunctional silanes. Particle formation and growth was studied under different experimental conditions (e.g. temperature and lead precursor concentrations) where nucleation and aggregation processes occurred. Determination of the average particle size was done by XRD. Transmission electron microscopy was also used to determine particle diameter as well as particle size distribution. Optical absorption spectra were measured at the UV-VIS wavelength range. Absorption edge blue shifts showed the quantum confinement effect in these materials. The non-hydrolyzed groups bonded to the silane prevented uncontrolled nucleation and aggregation during the particle formation and growth, i.e. at the solution stage by the homogeneous distribution of the Pb salts or at the xerogel state by the capping of the growing particles.
TL;DR: In this article, spherical wurtzite GaN nanoparticles with diameters of 5-8 nm were synthesized through a new gas reaction route, which showed significant blueshift compared with the band-gap emission from bulk GaN crystals.
Abstract: Spherical wurtzite GaN nanoparticles with diameters of 5–8 nm were synthesized through a new gas reaction route. The concave-surface-induced nucleation process based on the surface roughness of the substrate played an important role in the formation of quantum dots. Photoluminescence spectrum revealed the quantum-confined excited states in the nanoparticles with features at 3.73 eV (332 nm) and 3.85 eV (322 nm), which show significant blueshift compared with the band-gap emission from bulk GaN crystals. Four blue emission bands with low intensity, centered at 2.85 eV (435 nm), 2.75 eV (451 nm), 2.67 eV (464 nm), 2.62 eV (473 nm) respectively, were also observed. These blue bands may originate from surface states.
TL;DR: In this article, the nonlinear optical properties of the GaSb-SiO2 composite film have been studied at 632.8 nm by use of Z-scan technology, and the appearance of two photon absorption is predicted energetically above the exciton resonance for quantum-dot radii, which are between the electron and hole radii.
Abstract: Nanocrystalline GaSb embedded in SiO2 film was grown by radio frequency co-sputtering. The nonlinear optical properties of the GaSb–SiO2 composite film have been studied at 632.8 nm by use of Z-scan technology. The appearance of a two photon absorption is predicted energetically above the exciton resonance for quantum-dot radii, which are between the electron and hole radii. The nonlinear refractive index of the GaSb–SiO2 composite film is positive. It shows that the GaSb–SiO2 composite film posses a large third-order nonlinear susceptibility about 7.84×10−9 esu. Room temperature transmission spectrum shows that the absorption edge exhibits a very large blue shift of 2.7 eV compared with that of bulk GaSb, which is mainly explained by the quantum confinement effect.
TL;DR: In this paper, the electronic structures of the inhomogeneous quantum dots within the framework of the effective mass theory were investigated. And the results showed that the energies of electron and hole states depend sensitively on the relative magnitude 77 of the core radius to the capped quantum dot radius.
Abstract: We investigate the electronic structures of the inhomogeneous quantum dots within the framework of the effective mass theory. The results show that the energies of electron and hole states depend sensitively on the relative magnitude 77 of the core radius to the capped quantum dot radius. The spatial distribution of the electrons and holes vary significantly when the ratio eta changes. A quantum-confinement-driven type-II-type-I transition is found in GaAs/AlxGa1-xAs-capped quantum dot structures. The phase diagram is obtained for different capped quantum dot radii. The ground-state exciton binding energy shows a highly nonlinear dependence on the innner structures of inhomogeneous quantum dots, which originates from the redistribution of the electron and hole wave functions.
01 Jan 2000
TL;DR: In this paper, a multi-quantum well (MQW) structure was proposed to detect infrared radiation using the basic principles of quantum mechanics, which can be solved by the time independent Schrodinger equation.
Abstract: The idea of using multi-quantum well (MQW) structures to detect infrared radiation can be explained by using the basic principles of quantum mechanics. The quantum well is equivalent to the well known particle in a box problem in quantum mechanics, which can be solved by the time independent Schrodinger equation. Solutions to this problem involve the Eigen-values that describe the energy levels inside the quantum well in which the particle is allowed to exist. The position of the energy levels is primarily determined by the quantum well dimensions such as height and width. The chapter discusses quantum well infrared photodetectors (QWIP) that utilize the photo excitation of the electron (hole) between the ground state and the first excited state in the conduction band quantum well. The quantum well structure is designed so that these photo-excited carriers can escape from the quantum well and be collected as photocurrent. In addition to larger intersub-band oscillator strength, these detectors afford greater flexibility than extrinsically doped semiconductor infrared detectors because the wavelength of the peak response and cutoff can be continuously tailored by varying layer thickness and barrier composition.
TL;DR: The method of few-body physics is applied to the calculation of the low-lying states of the exciton of a GaAs disk-like quantum dot with a parabolic potential as discussed by the authors.
Abstract: The method of few-body physics is applied to the calculation of the low-lying states of the exciton of a GaAs disk-like quantum dot with a parabolic potential. The binding energy of the exciton in quantum disks is calculated for two different thicknesses as a function of the disk size. The four lowest exciton states dependent on the disk thickness are investigated.
TL;DR: In this paper, the authors calculate the energy spectrum of hydrogen impurity located in the center of parabolic quantum dot and show that the degeneracy of the energy levels is quite different from the case of spherical quantum dot.
TL;DR: In this paper, the authors studied the evolution of the optical absorption of free-standing PS films during thermal oxidation at 200°C in air and showed that the optical gap associated with each crystallite should increase during the thermal oxidation process, due to the quantum confinement effect.
Abstract: We have systematically studied the evolution of the optical absorption of free- standing PS films during thermal oxidation at 200°C in air. Our experiment results show the evolution of transmission curve is quite complicated, which red-shifts first and then blue- shifts during thermal oxidation. At the same time, the transmission at the low energy decreases first and then increases. We propose an explanation as follows: (1) the energy gap associated with each crystallite should increase during thermal oxidation process, due to the quantum confinement effect; (2) the energy gap should decrease with an increase in oxygen termination atoms. Both the increasing of the gap due to the quantum confinement effect and the decreasing of the gap due to the Si-O bond formation cause a complicated evolution of optical absorption.
02 May 2000
TL;DR: In this article, the SbSI quantum dot composites are used for electro-optical devices with high dielectric permittivity, high electrooptical coefficient and high photoconductivity.
Abstract: Semiconducting ferro electric antimony sulphoiodide (SbSI) microcrystallite doped organically modified TiO2 thin film and bulk solids are successfully fabricated by the sol- gel process Ferro electric SbSI crystallites have some attractive properties, including high dielectric permittivity, high electro-optical coefficient and high photoconductivity SbSI is also an intrinsic semiconductor with a relatively narrow energy gap If the crystal size is near its Bohr radius and the microcrystallites are dispersed in a suitable matrix, a dramatic improvement of the third order non linearity will be achieved due to the quantum confinement effect It is clear that the SbSI quantum dot composites are good candidates for electro-optical devices Glycidoxypropyltrimetroxysilane modified TiO2 is used as the matrix and SbSI is synthesized in situ by using SbI3 SC9NH2)2 and H2S gas The size is controlled by the heat-treatment conditions and is characterized by the XRD and HRTEM measurements The optical absorption spectrum gives evidence of the quantum confinement effect The third order susceptibility of the SbSI quantum dot is measured by the degenerate four wave mixing method© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only
TL;DR: In this article, the authors have successfully prepared composite films of GaAs 0.57 Sb 0.43 -SiO 2 onto glass substrates by radio frequency magnetron co-sputtering.
TL;DR: A Comment on the Letter by Y. K. Chang et al. as discussed by the authors, Phys. Rev. Lett. 82, 5377 (1999) is given in the Appendix.
Abstract: A Comment on the Letter by Y. K. Chang et al., Phys. Rev. Lett. 82, 5377 (1999). The authors of the Letter offer a Reply.
TL;DR: In this article, the authors investigated the dependence of exciton photoluminescence spectra of ZnS-ZnSe quantum wells with different localization-center concentrations on the excitation intensity and temperature.
Abstract: A study is reported on the dependence of exciton photoluminescence spectra of ZnS-ZnSe quantum wells with different localization-center concentrations on the excitation intensity and temperature. The shape of the experimental low-temperature photoluminescence band is shown to agree well with that calculated in a model of exciton hopping to the nearest localization center and in one that takes into account transitions of a localized exciton to all centers in its local environment. The parameters characterizing localized excitons in these quantum structures of a submonolayer thickness have been determined.
TL;DR: In this article, the authors used the admittance spectroscopy technique to study the energy levels of subbands in SiGe/Si quantum well and found that the value of activation energy increased with increasing well width, in accordance with the quantum confinement effect.
Abstract: Using the admittance spectroscopy technique, energy levels of subbands in SiGe/Si quantum well are studied. The value of activation energy increases with increasing well width, in accordance with the quantum confinement effect. Two conductance peaks due to hole emission from heavy hole ground state and light hole ground state were observed. It was found that the value of activation energy increased with annealing time at the temperature of 800° C, while the activation energy decreases with the annealing time at 900° C.
TL;DR: In this article, the differential transmittance of Ge quantum dots, with average radius between 4 and 16 nm, in the sub-picosecond time domain was investigated, and the response was probed in the spectral range 450 to 750 nm, including in this way the E1 and E1 +Δ1 spectral structures, which have a partially excitonic nature.
Abstract: We here report on an investigation of the differential transmittance of Ge quantum dots, with average radius between 4 and 16 nm, in the subpicosecond time domain. Pump pulses of 390 nm have been used, and the response has been probed in the spectral range 450 to 750 nm, including in this way the E1 and E1 +Δ1 spectral structures, which have a partially excitonic nature. It is shown that the observed features can be essentially explained in terms of (i) occupancy of the conduction states by the photoexcited carriers and (ii) their correlation–exchange interactions. A comparison with the ultrafast response of Ge bulk is also carried out. Finally, the screening of the excitonic interaction and the presence of quantum confinement effect are discussed.
TL;DR: Amorphous silicon quantum dots (a-Si QDs), which show a quantum confinement effect, were grown in a silion nitride film by plasma enhanced chemical vapor deposition.
Abstract: Amorphous silicon quantum dots (a-Si QDs), which show a quantum confinement effect, were grown in a silion nitride film by plasma enhanced chemical vapor deposition. Red, green, blue, and white photolumiscence were observed from the a-Si QD strictures by controlling the fot size. An organe light-emitting device (LED) was fabricated using a-Si QDs with a mean size of 2.0 nm. The turn-on vottage was less than 5 V. An external quantum effiency of 2×10 −3 % was also demonstrated. These results show that an LED using a-Si QDs embedded in the silicon nitride film is superior in terms of electrical and optical properties to other Si-based LEDs.
TL;DR: In this paper, the quantum confinement effect of an electron-hole pair with higher angular momenta in spherical quantum dots is investigated and the exciton confinement picture is realized in the weak confinement region even for such higher excited states.
29 Nov 2000
TL;DR: In this paper, the effect of 1D quantum confinement on low-dimensional dilated magnetic semiconductors has been studied by time-resolved photoluminescence, which shows the formation processes of magnetic polarons of excitons.
Abstract: Low-dimensional diluted magnetic semiconductors have been made by epitaxy and microfabrication techniques. Multiple quantum wells of the Cd 1-x Mn x Te/ZnTe (x equals 0.1) system were grown by molecular beam epitaxy. Quantum wires of Cd 1-x Mn x Se (x equals 0.08) were fabricated from the quantum well of Cd 1-x Mn x Se/ZnSe by the electron beam lithography. Quantum dots of Cd 1-x Mn x Se (x equals 0.03) were grown by the self-organization mode on a ZnSe layer. Magneto-optical properties of these low dimensional structures were studied by time-resolved photoluminescence. The transient photoluminescence in the Cd 1-x Mn x Te/ZnTe multiple quantum wells shows the formation processes of magnetic polarons of excitons. The exciton luminescence from the quantum wires of Cd 1-x Mn x Se displays the influence of the 1D quantum confinement effect for the exciton states with the effective g-value of 100 - 150. The exciton luminescence from the wires is linearly polarized parallel to the wire direction. The exciton luminescence in the quantum dots shows the strong confinement effect of the exciton energy corresponding to the dot size of 4 - 6 nm as well as large effective g-value of 89. The quantum dot excitons also exhibit marked increase of the luminescence lifetime with increasing the magnetic field, which is caused by suppression of the non-radiative process due to the shrinkage of the exciton wavefunction.