Showing papers on "Potential well published in 2001"
TL;DR: Amorphous silicon quantum dots (a-Si QDs), which show a quantum confinement effect were grown in a silicon 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 silicon nitride film by plasma-enhanced chemical vapor deposition. Red, green, blue, and white photoluminescence were observed from the a-Si QD structures by controlling the dot size. An orange light-emitting diode (LED) was fabricated using a-Si QDs with a mean size of 2.0 nm. The turn-on voltage was less than 5 V. An external quantum efficiency of 2×10−3% was also demonstrated. These results show that a 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.
379 citations
TL;DR: In this paper, Solgel films containing manganese-doped CdS nanocrystals are synthesized and the spectra and kinetics of the Mn2+ ion emission at room temperature have been studied.
Abstract: Sol–gel films containing manganese-doped CdS nanocrystals are synthesized. Photoluminescence spectra and kinetics of the Mn2+ ion emission at room temperature have been studied. It is found that the quantum confinement effect does not modify the emission lifetime as compared to bulk material.
34 citations
TL;DR: In this article, thin films of GaAs were electrochemically prepared from acidic solutions of pure metallic Ga and As 2 O 3, and structural characterization of the nanoparticles were carried out by XRD technique which exhibits partial amorphization of the crystallites in the low electrolysis current regime.
30 citations
TL;DR: In this article, the evolution of valence-band spectra during Si layer thinning in a silicon-on-insulator (SOI) substrate by X-ray photoelectron spectroscopy (XPS) was studied.
Abstract: We have studied the evolution of valence-band spectra during Si layer thinning in a silicon-on-insulator (SOI) substrate by X-ray photoelectron spectroscopy (XPS) in order to observe the quantum-confinement effect in two-dimensional Si It was clearly observed that the valence-band maximum (VBM) shifts towards higher binding energies with decreasing Si thickness (< ~10 nm) The VBM shifts were ascribed to vertical confinement of heavy holes in the quantum-well structure of a vacuum/single-crystalline Si/buried amorphous SiO2
20 citations
TL;DR: Angle-resolved photoemission spectra from Na adlayers on Al(111) reveal features which behave like quantum well resonances although the substrate provides no confining barrier, and the quantum well behavior is shown to be due to surface resonances of the Na/Al system.
Abstract: Angle-resolved photoemission spectra from Na adlayers on Al(111) reveal features which behave like quantum well resonances although the substrate provides no confining barrier. These features are observed in a narrow photon energy range where overlayer collective excitations cause resonant enhancement of the photoemission intensity. The quantum well behavior is shown to be due to surface resonances of the Na/Al system. The resonances are observable using photoemission because of spatial confinement and dynamical enhancement of the local electric field within the Na films.
17 citations
TL;DR: In this article, the position of fundamental absorption edge partially depends on the composition of the ZnO/TiO2 nanocomposite films, and shifts toward a shorter wavelength with the increasing content of ZnOs in the films.
Abstract: ZnO/TiO2 nanocomposite films on quartz substrates were prepared by the sol-gel method, and the corresponding optical absorption properties were investigated. In the ultraviolet region, it was found that the position of fundamental absorption edge partially depends on the composition of the ZnO/TiO2 films, and shifts toward a shorter wavelength with the increasing content of ZnO in the films. Moreover, a blueshift of the absorption edge resulted from a quantum size effect and the quantum confinement effect was observed in the ZnO/TiO2 system.
15 citations
TL;DR: In this article, carbon ions were implanted into Si/ZSM-5 host-guest composite material at an energy of 50 keV and with a dose of 3×10 17 cm −2 followed by thermal annealing in a vacuum chamber to form SiC and ZSM composite material.
15 citations
TL;DR: In this article, high-resolution transmission electron microscope (HRTEM) photographs show that the CdSe core has a wurtzite crystal structure and the shell of HgSe has a hexagonal structure.
15 citations
TL;DR: In this article, anisotropic alignment of the exciton dipole moments in the quantum wires of Zn 1− x − y Cd x Mn y Se was observed in a magnetic field.
Abstract: Diluted magnetic semiconductor quantum wires of Zn 1− x − y Cd x Mn y Se were fabricated by the electron beam lithography and wet chemical etching techniques. Photoluminescence spectra for the quantum wires with different wire width indicate evident quantum confinement effect and linear polarization effect, which may imply the anisotrophic alignment of the exciton dipole moments in the quantum wires. Large Zeeman effect accompanied by a suppression of the nonradiative recombination procedure of the excitons were observed in a magnetic field.
15 citations
TL;DR: In this paper, a cluster-based nanostructured films of Si clusters embedded in SiO nanoparticles have been prepared by low energy deposition of SiO cluster beam formed by inert gas aggregating method.
13 citations
TL;DR: In this paper, the confining potential is derived from 3D self-consistent Poisson-Thomas-Fermi calculations, and the sequence of decay lifetimes provides a sensitive test of the confined potential and its dependence on electron occupation.
Abstract: Recent measurements of electron escape from a nonequilibrium charged quantum dot are interpreted within a two-dimensional (2D) separable model. The confining potential is derived from 3D self-consistent Poisson-Thomas-Fermi calculations. It is found that the sequence of decay lifetimes provides a sensitive test of the confining potential and its dependence on electron occupation.
TL;DR: InAs0.4P0.6 nanocrystals with a size of 4.3-6.5 µm were found to exhibit the behavior of a direct bandgap.
Abstract: InAs0.4P0.6 nanocrystals with a size of 4.3-6.5 nm embedded in SiO2 thin films were prepared by the radio-frequency magnetron co-sputtering technique. X-ray diffraction and Raman spectra strongly suggest the existence of InAs0.4P0.6 nanocrystals in SiO2 matrices. The size distribution of the nanocrystals was observed by transmission electron microscopy. The optical transmission spectra indicate that the optical absorption band edge of the composite thin films can be modulated in a very large wavelength range by changing the preparation conditions. The InAs0.4P0.6 nanocrystals exhibit the behaviour of a direct bandgap. The marked blue shift of the optical absorption edge with respect to the bulk semiconductor can be explained by the quantum confinement effect.
TL;DR: In this article, the evolution of the optical absorption and emission properties of Ga1−xInxN/GaN double quantum wells grown on (0001)-oriented sapphire substrates with varying well width has been investigated by spectroscopic ellipsometry and photoluminescence.
Abstract: The evolution of the optical absorption and emission properties of strained Ga1−xInxN/GaN double quantum wells grown on (0001)-oriented sapphire substrates with varying well width has been investigated by spectroscopic ellipsometry (SE) and photoluminescence (PL). The SE result shows that the band-gap absorption energy of the wells shifts to higher energies as the well width decreases, indicating a quantum-confinement effect. The decreasing trend agrees with the result of one-dimensional square-well potential calculations. The PL result shows a Stokes shift of the emission edge from the corresponding absorption edge, attributable to the combined effects of the strain-induced piezoelectric potential and the In-fluctuation potential in the well. The blueshift of the emission edge with increasing PL excitation density further supports the existence of a strong piezoelectric field in the well.
23 Apr 2001
TL;DR: In this paper, high quality ZnO/Zn1MgO multi-quantum wells (MQWs) have been prepared on lattice-matched ScAIMgO4 substrates by laser-MBE method.
Abstract: High quality ZnO/Zn1MgO multi-quantum wells (MQWs) have been prepared on lattice-matched ScAIMgO4 substrates by laser-MBE method. Nine pixels of MQWs having different well widths were integrated in the same substrate by means of combinatorial masking techniques, which provided excellent specimens to systematically study the dependence of physical properties of MQWs on well widths. Optically pumped stimulated emission spectra were measured in these ZnO/Zn1MgO multi-quantum wells by using a tunable pulsed dye laser as excitation source. We investigated the pump-intensity dependence of the stimulated emission spectra from 5 to 300 K. At low temperatures, only one peak in the stimulated emission was observed, which could be assigned to the emission induced by exciton-exciton inelastic scattering (P-band). When the temperature increases above 160 K, there appears an additional peak at the lower energy side of the P-band, which was assigned to electronhole plasma emission. However, the emission due to the exciton-exciton scattering still remains up to room temperature. The gain spectrum for a multi-quantum well sample has been obtained by variable stripe method at room temperature. At an excitation intensity of about 2 MW/cm2, the peak gains for the P-band and electron-hole plasma emission are 239 cm1 and 380 cm1, respectively. The exciton binding energy was deduced from the energy difference between the P-band and free exciton band. The exciton binding energies of these samples having different well widths were found to increase with decreasing the well widths due to the quantum confinement effect. This enhancement of exciton binding energy should be favorable for the stability of exciton states at higher temperatures.
TL;DR: In this paper, the vibrational spectra of mixed cadmium sulfoselenide nanocrystals in a fluorophosphate glass matrix are investigated by Raman spectroscopy.
Abstract: The vibrational spectra of mixed cadmium sulfoselenide nanocrystals in a fluorophosphate glass matrix are investigated by Raman spectroscopy. The asymmetry of the lines of the fundamental modes of nanocrystals is experimentally observed in the region of lattice vibrations, which is interpreted as a quantum confinement effect. In the framework of the model of confined phonons, the contribution of the band states to the Raman scattering spectrum is calculated and the size of nanocrystalline regions is estimated. The results obtained are in good agreement with the data on the low-frequency Raman scattering in these objects.
TL;DR: In this paper, optical absorption data when analyzed with Mie's scattering formula give results which indicate a metal-insulator type transition in the case of silver particles having diameters around 3nm.
TL;DR: In this article, the authors analyzed the structure and growth behavior of InP-SiO2 composite films under different preparation conditions and discussed the possible transition of the direct band gap to the indirect band gap.
Abstract: InP nanoparticles embedded in SiO2 thin films were prepared by radio-frequency magnetron co-sputtering. We analyzed the structure and growth behavior of the composite films under different preparation conditions. X-ray diffraction and Raman spectroscopy analyses indicate that InP nanoparticles have a polycrystalline structure. The average size of InP nanoparticles is in the range of 3–10 nm. The broadening and red shift of the Raman peaks were observed, which can be interpreted by the phonon confinement model. Optical transmission spectra indicate that the optical absorption edges of the films can be modulated in the visible light range. The marked blue shift of the absorption edge with respect to that of bulk InP is explained by the quantum confinement effect. The theoretical values of the blue shift predicted by the effective mass approximation model are different from the experimental results for the InP-SiO2 system. Analyses indicate that the exciton effective mass of the InP nanoparticles is not constant and is inverse relative to the particles radius, which may be the main reason that results in the discrepancy between the theoretical and the experimental result. We discussed the possible transition of the direct band gap to the indirect band gap for InP nanoparticles embedded in SiO2 thin films.
TL;DR: In this article, the temperature dependence of the photoluminescence from V-grooved GaAs/AlGaAs quantum wires was investigated and it was shown that in the processes of real space carrier transfer from the vertical quantum well region to quantum wire region a 3.5 meV thermal activation energy has been experimentally observed in their sample.
TL;DR: SiO2 composite thin films containing InP nanocrystals were fabricated by radio-frequency magnetron co-sputtering technique and the microstructure of the composite thin film was characterized by X-ray diffraction and Raman spectrum as mentioned in this paper.
Abstract: SiO2 composite thin films containing InP nanocrystals were fabricated by radio-frequency magnetron co-sputtering technique. The microstructure of the composite thin films was characterized by X-ray diffraction and Raman spectrum. The optical absorption band edges exhibit marked blueshift with respect to bulk InP due to strong quantum confinement effect. Non-linear optical absorption and non-linear optical refraction were studied by a Z-scan technique using a single Gaussian beam of a He-Ne laser (632.8 nm). We observed the saturation absorption and two-photon absorption in the composite films. An enhanced third-order non-linear optical absorption coefficient and non-linear optical refractive index were achieved in the composite films. The nonlinear optical properties of the films display the dependence on InP nanocrystals size.
Patent•
28 Sep 2001
TL;DR: In this paper, a micro optical resonator of light wavelength size used for a light-emitting element and a laser element wherein a light emission intensity is raised in non-linearity of at least single-multiplication of an input power related to light emission intrinsic to a lightemission layer, for improved dependency of the light emissions on the input power.
Abstract: PROBLEM TO BE SOLVED: To provide a micro optical resonator of light wavelength size used for a light-emitting element and a laser element wherein a light-emission intensity is raised in non-linearity of at least single-multiplication of an input power related to light emission intrinsic to a light-emission layer, for improved dependency of the light-emission intensity on the input power. SOLUTION: An optical active layer has a quantum confinement structure where micro particles about 1-10 nm in size, or quantum dot of material with large interaction between light and electron, are carried. The material with large interaction between light and electron has strong triggering power of an exciter while the quantum confinement effect bearing quantum dot is posed to generate a strong light emission. The strong light emission improves dependency of light-emission intensity on an input power.
TL;DR: The photoluminescence (PL) from silicon surfaces during photoelectrochemical etching processes was monitored in situ by using a confocal microprobe spectrometer.
Abstract: The photoluminescence (PL) from silicon surfaces during photoelectrochemical etching processes was monitored in situ by using a confocal microprobe spectrometer. The etching time, laser power, polarization potential and the resistance of silicon were found to remarkably influence the formation of porous silicon (PS). For the high resistance silicon sample, the PL band intially increases in intensity and blueshifts with the progress of etching, then decreases and stops shifting. The higher the laser power is, the stronger the PL intensity and the shorter the wavelength could be. For the low resistance silicon sample, no clear shift in the wavelength could be found with the progress of etching. These results were interpreted by the quantum confinement effect together with the influence of electrochemical reaction equilibrium and the surface oxidation species on the formation of PS.
01 Jan 2001
TL;DR: In this article, the parabolic potential is defined with a β-parameter chosen so that it results in the same E0 groundstate energy as for the spherical quantum dot of radius R and rectangular potential in the absence of the impurity.
Abstract: The evidence of a parabolic potential well in quantum wires and dots was reported in the literature, and a parabolic potential is often considered to be a good representation of the “barrier” potential in semiconductor quantum dots. In the present work, the variational and fractionaldimensional space approaches are used in a thorough study of the binding energy of on-center shallow donors in spherical GaAs-Ga1-xAlxAs quantum dots with potential barriers taken either as rectangular [V b (eV) ??1.247 x for r >] or parabolic [Vb (r) ??β2?r2] isotropic barriers. We define the parabolic potential with a β?parameter chosen so that it results in the same E0 groundstate energy as for the spherical quantum dot of radius R and rectangular potential in the absence of the impurity. Calculations using either the variational or fractional-dimensional approaches both for rectangular and parabolic potential result in essentially the same on-center binding energies provided the dot radius is not too small. This indicates that both potentials are alike representations of the quantum-dot barrier potential for a radius R quantum dot provided the parabolic potential is defined with?β?chosen as mentioned above.
TL;DR: In this article, a GaAs(N) nanostructured thin films have been deposited using the radio frequency sputtering technique and the measured nanowisker average diameter range about 3.9 to 4.1 nm.
Abstract: GaAs(N) nanostructured thin films have been deposited using the radio frequency sputtering technique. Films are formed by filament-like nanocrystallites with a sharp grain size distribution. The measured nanowhisker average diameter range about 3.9 to 4.1 nm. The film structure was cubic with a preferential (1,1,1) orientation. Particle size effects were observed in the photoluminescence emission spectra. The blue emission (λ = 425-432 nm) was due to the quantum confinement effect with a effective band gap of 2.92 eV and a quantum yield of about 92% of efficiency.
TL;DR: In this paper, the authors show that the binding energy of the shallow impurity ground state is strongly reduced by the presence of a metallic mirror at a few effective Bohr radii from the quantum well.
Abstract: We show that the binding energy of the shallow impurity (at the center of the quantum well) ground state is strongly reduced by the presence of a metallic mirror at a few effective Bohr radii from the quantum well. For a given depth of the quantum well, we find that the absolute value of the image potential energy without the metallic mirror is equal to that with a fixed metallic mirror while a certain width of the quantum well is met. Hence, it is proposed that the binding energy of the shallow impurity ground state in the quantum well with and without the metallic mirror can be separately measured by the variation of the width of quantum well. The contribution of the image potential energy to the binding energy of the shallow impurity ground state may then be deduced.
22 Oct 2001
TL;DR: In this paper, micro-Raman measurements were carried out to investigate the microstructure of a-Si:H samples prepared by plasma enhanced chemical vapor deposition (PECVD) using 647.1 nm and 514.5 nm laser lines as excitation sources.
Abstract: Micro-Raman measurements were carried out to investigate the microstructure of a-Si:H samples prepared by plasma enhanced chemical vapor deposition (PECVD) using 647.1 nm and 514.5 nm laser lines as excitation sources. It is found that the frequency of TO mode downshifts with increasing excited photon energy without significantly changing its width, while LO mode expands to a large extent. The above results suggest that the variation of LO and TO mode is caused by resonant Raman effect. With the increasing of excitation energy, smaller a-Si clusters are excited thus results in large redshift of TO band according to the quantum confinement effect, another possible explanation may be related with the existing of a highly disordered layer near the free surface in a-Si:H film. In conjunction with observation of LO band variation, we further deduce that the highly disordered layer may have lower H content.
TL;DR: In this paper, the ground-state energy and the compressibility for the interacting electron-hole plasma in semiconductor quantum wells are discussed taking into account finite well width and strain effects as a function of sheet carrier density.
Abstract: The ground-state energy and the compressibility for the interacting electron-hole plasma in semiconductor quantum wells are discussed taking into account finite well width and strain effects as a function of sheet carrier density. Many-body effects are evaluated within the Hartree-Fock approximation and the valence-band nonparabolicity due to band mixing is examined by solving the Luttinger-Kohn Hamiltonian. The results are applied to In x Ga 1-x As/InGaAsP/InP quantum wells and we observe that the ground-state energies are lowered with increasing sheet carrier density and quantum confinement effect. These variations of ground-state energy depending on the sheet carrier density and the quantum confinement effect have considerable effects on the thermodynamic compressibility of electrons and holes.
TL;DR: In this article, the conduction band minimum (CBM) profile was calculated to determine the distribution of strain inside hemispherical InAs quantum dots (QDs) embedded in GaAs.