Showing papers on "Potential well published in 1995"
TL;DR: In this article, carbon ions were implanted into crystal silicon wafers at an energy of 50 keV and with a dose of 1017 cm−2 followed by thermal annealing.
Abstract: Carbon ions were implanted into crystal silicon wafers at an energy of 50 keV and with a dose of 1017 cm−2 followed by thermal annealing. A layer of polycrystalline β‐SiC was formed beneath the sample surface. Porous nanometer structures were prepared by conventional anodization. At room temperature, the samples exhibit a blue luminescence peak at 2.79 eV (445 nm), which is higher than the energy gap of bulk β‐SiC (2.2 eV), and its intensity is stronger than that of the reference porous silicon. The results could be explained by the quantum confinement effect.
139 citations
TL;DR: In this paper, single hole quantum dot transistors are fabricated in silicon-on-insulator and strong oscillations in drain current as a function of the gate voltage have been observed at temperatures over 81 K and drain biases over 66 mV.
Abstract: Novel p‐channel quantum‐dot transistors were fabricated in silicon‐on‐insulator. Strong oscillations in the drain current as a function of the gate voltage have been observed at temperatures over 81 K and drain biases over 66 mV. The oscillations are attributed to holes tunneling through the discrete single hole energy levels in the quantum dot. Measurements show that the average energy level spacing is ∼35 meV. Simple modeling indicates that about two thirds of the energy level spacing come from the Coulomb interaction between holes (i.e., hole Coulomb blockade) and one third from the quantum confinement effect. The realization of single hole quantum‐dot transistors opens new possibilities for innovative circuits that utilize complementary pairs of quantum‐dot transistors.
127 citations
TL;DR: In this paper, the mechanisms of new photoluminescence phenomena appearing in nanostructured materials in terms of quantum confinement effect, impurity and defect energy levels in the energy gap and destruction of selection rules of electronic transitions are discussed.
69 citations
Patent•
22 Aug 1995TL;DR: In this article, a quantum well semiconductor light emitting devices such as lasers that utilize resonant tunneling for carrier injection and spatially-diagonal transitions between an energy state in the conduction band of one quantum well and an energy states in the valence band of the adjacent quantum well for light emission, resulting in much improvement in both radiative efficiency and carrier injection efficiency.
Abstract: The present invention relates to quantum well semiconductor light emitting devices such as lasers that utilize resonant tunneling for carrier injection and spatially-diagonal transitions between an energy state in the conduction band of one quantum well and an energy state in the valence band of the adjacent quantum well for light emission, resulting in much improvement in both radiative efficiency and carrier injection efficiency. An elementary structure of the invented devices comprises two spatially coupled quantum wells residing in conduction and valence bands respectively wherein the valence band-edge in one quantum well is higher than the conduction band-edge of the other quantum well. Each quantum well contains at least one energy state formed by the quantum size effect. Light emission occurs by the transition of electrons from the state which is higher in energy in the conduction band quantum well to the state in the valence band quantum well, and the emission wavelength is inversely proportional to the energy difference between the two states which can be easily tailored by adjusting quantum well thicknesses. Cascade emission is realized in a superlattice structure which is constructed by periodically stacking many repeated elementary device structures.
57 citations
TL;DR: In this paper, a new class of Si-based quantum well structures (QWs), called neighboring confinement structure (NCS), was observed, which consists of a single pair of tensile−strained−Si layer and a compressivestrained Si layer sandwiched by completely relaxed Si1−xGex layer.
Abstract: Intense photoluminescence (PL) was observed from a new class of Si‐based quantum well structures (QWs), that is, neighboring confinement structure (NCS). NCS consists of a single pair of tensile‐strained‐Si layer and a compressive‐strained Si1−yGey layer sandwiched by completely relaxed Si1−xGex ( layers. In spite of the indirect band structure in real and k spaces, radiative recombination was enhanced compared with not only type‐II strained‐Si/relaxed‐Si1−xGex QWs but also type‐I strained‐Si1−yGey/relaxed‐Si1−xGex QWs. PL without phonon participation was found to dominate the spectrum possibly due to the effective carrier confinement for both electrons and holes. Quantum confinement effect was clearly observed by varying the well width, showing that the expected band alignment is realized.
41 citations
TL;DR: In this paper, it is demonstrated that the blue emission is due to direct transitions in silicon nanocrystallites which are caused by a quantum confinement effect, and a model is proposed to understand the enhancement of the direct transitions.
Abstract: Intense blue luminescence with decay lifetimes of 100–500 ps is observed from nanocrystalline silicon thin films at room temperature. The grain size reduction of the silicon crystallites to 3–5 nm leads to the generation of the luminescence. It is demonstrated that the blue emission is due to direct transitions in silicon nanocrystallites which are caused by a quantum confinement effect. The contribution of silicon dioxide to the blue emission is excluded. A model is proposed to understand the enhancement of the direct transitions in silicon nanocrystallites.
30 citations
TL;DR: In this paper, the authors studied the temperature dependence of the photoluminescence intensity in strain-confined GaAs and showed that there is no reduction of luminescence efficiency at low temperature, and that high quantum efficiency persists to significantly higher temperature.
Abstract: By studying the temperature dependence of the photoluminescence intensity in strain-confined GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wires and quantum dots, we show that as dimensionality is reduced from two-dimensional (2D) through 1D to 0D, there is no reduction of luminescent efficiency at low temperature, and that high quantum efficiency persists to significantly higher temperature. There is efficient spatial energy transfer from the 2D region to the 1D or 0D region. This transfer increases with temperature, showing that there is a barrier to transfer a few meV high. This barrier is lower than theoretically predicted. For above band-gap excitation there is substantial ``capture transfer'' in which unthermalized carriers or excitons transfer even at very low temperature. Exciton localization due to the well-width fluctuations of the host quantum well also plays an important role in determining the temperature dependence of the exciton transfer in these structures.
26 citations
TL;DR: In this paper, a simple quantum mechanical model has been used to calculate the particle size from the absorption onset measured for CdS in the SiO2 matrix, interpreted in terms of a quantum confinement effect of small crystal size.
25 citations
25 citations
TL;DR: An alternative description of the coherence volume, related closely to the localization length, is developed, which can be related to the spectrum of Huctuations in the exciton's potential energy as it moves in the plane of the quantum well.
Abstract: We investigate the absorption spectrum and the distribution of radiative decay times for two-dimensional excitons in semiconductor quantum wells, as affected by a random adiabatic in-plane excitonic potential. We limit our discussion to the case of a white-noise potential. Such a potential could arise as a result of fluctuations in the composition of an alloy semiconductor, or alternatively, fluctuations in quantum-well thickness. We find, in general, that the shortest radiative decay time is directly proportional to the inhomogeneous broadening of the exciton line in absorption, which in turn is proportional to the correlation parameter of the random potential. We calculate the magnitude of the correlation parameter for several cases of potential interest. The theory is in qualitative agreement with available experimental data.
22 citations
TL;DR: In this article, carbon ions were implanted into silicon crystal wafers with doses of 1014−1017 cm−2 at an energy of 50 keV followed by thermal annealing and anodization to form porous β-SiC.
TL;DR: In this paper, the potential energy landscape of solid hcp 4He in the vicinity of the 0 K crystal structure using an accurate pair potential was studied, and it was shown that the atomic arrangements that lie at local minima in the potential landscape (inherent structures) are glassy and porous, and have much lower potential energy than the crystalline form at the same density.
Abstract: We study the potential energy landscape (many‐atom potential energy as a function of atomic positions) of solid hcp 4He in the vicinity of the 0 K crystal structure using an accurate pair potential. At the melting point, the potential energy of the helium lattice is far above the minimum hcp interatomic potential energy. We confirm previous conclusions (based on less accurate potentials) that all of the classical phonon frequencies at the 0 K melting pressure are imaginary, indicating that the melting‐point crystal corresponds to a local maximum in the potential landscape; a pressure of about 1300 bar, however, makes it a local minimum. We find that the atomic arrangements that lie at local minima in the potential landscape (‘‘inherent structures’’) are glassy and porous, and have much lower potential energy than the crystalline form at the same density. We have quantitatively characterized the glassy structures by their radial distribution functions and coordination number distributions; they qualitatively resemble inherent structures for classical monatomic liquids, but exhibit differences of detail. A model variational calculation has been carried out for the melting‐density ground state. It utilizes separate basis functions for each of the inherent structures, predicts a large Lindemann ratio for the crystal, and indicates that the probability distribution is a maximum at the perfect lattice configuration.
TL;DR: In this paper, a semi-empirical tight-binding scheme for the (ZnS)n/(Si2)m (110) superlattices with a wide range of n,m≤20 was proposed to integrate the superior properties of ZnS with the mature technology of Si.
Abstract: The optimal epilayers on a silicon substrate are suggested to integrate the superior properties of ZnS semiconductor with the mature technology of Si. In a semiempirical tight‐binding scheme, the band structures and optical transitions are studied for the (ZnS)n/(Si2)m (110) superlattices with a wide range of n,m≤20. Because of the quantum confinement effect caused by the large band‐gap ZnS layers, the band‐edge states are confined two dimensionally in the Si quantum wells. A single empty interface band is found lying below the conduction band. Furthermore, the influence of valence‐band discontinuity has been checked over all possible energy ranges. The optical matrix elements of the superlattices are calculated and compared with those of bulk ZnS and Si.
TL;DR: In this paper, a free-standing GaAs whisker is fabricated by selective area growth based on reduced-pressure metal-organic vapor-phase epitaxy, which shows a spectral blue shift due to the two-dimensional quantum confinement of the carriers.
Abstract: Nanometer-size free-standing GaAs whiskers are fabricated by selective area growth based on reduced-pressure metal-organic vapor-phase epitaxy. Photoluminescence measurements of these GaAs whiskers show a spectral blue shift due to the two-dimensional quantum confinement of the carriers. The spectral blue shift is, however, much smaller than the lowest level energy expected by the square-potential confinement. This is due to a band-gap reduction induced by the charge separation caused by the existence of surface depletion potential, which is confirmed by surface passivation experiments using sulfur compounds. Furthermore, intense light emission is observed during carrier injection to the p-n junction formed in the GaAs whisker. The emitted light shows strong polarization anisotropy, which can be explained by the quantum confinement effect. These results indicate that nano-whiskers offer high-quality quantum wire structures, which can be applied to ultra-small opto-electronic devices.
10 Dec 1995
TL;DR: In this paper, p-channel quantum-dot transistors were fabricated in silicon-on-insulator (SOI) and strong oscillations in the drain current as a function of the gate voltage have been observed at temperatures over 81 K and drain biases over 66 mV.
Abstract: Novel p-channel quantum-dot transistors were fabricated in silicon-on-insulator (SOI). Strong oscillations in the drain current as a function of the gate voltage have been observed at temperatures over 81 K and drain biases over 66 mV. Measurements show that the average energy level spacing is approximately 33 meV and it is due to both single hole charging effect and quantum confinement effect. A digital inverter using a complementary pair of n and p-channel quantum dot transistors is also proposed.
TL;DR: In this paper, the Coulomb interaction between the electron and the hole was shown to be equivalent to an effective potential acting on the center-of-mass of a three-dimensional exciton.
Abstract: The usual approach to the problem of excitons in semiconductor quan- tum wells is to assume that both the electron or the hole are primarily localized in the potential well regions defined by the band offsets, i.e., that the quantum wells are deep. We re-examine the problem of the exciton in the presence of a very shallow square well potential due to the (small) conduc- tion and valence band offsets in a semiconducting heterostructure. We show that the combined effects of the shallow well and the Coulomb interaction between the electron and the hole are equivalent to an effective potential acting on the center-of-mass of a three-dimensional exciton. We calculate the shape of such a potential and show it to be satisfactorily approximated by the potential of a parabolic well.
01 Jan 1995
TL;DR: In this paper, the authors discuss fabrication of GaAs quantum wires and dots using both selective growth and spontaneous growth technique in MOCVD, including the optical properties of those nano-structures.
Abstract: We discuss fabrication of GaAs quantum wires and dots using both selective growth and spontaneous growth technique in MOCVD, including the optical properties of those nano-structures. In the selective growth, triangular-shaped GaAs quantum wires as narrow as 7nm and quantum dots with 25nm lateral width were obtained. The quantum confinement effect is evidenced by photoluminescence (PL) and magneto-PL. On the other hand, self-organizing growth achieved InGaAs quantum dots with a diameter of 15nm. For characterization of the nanostructures, observation of photoluminescence from a single quantum dot was achieved. Finally, as the first step to the ultimate quantum lasers, a vertical microcavity quantum wire lasers was demonstrated.
09 Feb 1995
TL;DR: In this article, the exciton binding energy has been calculated as a function of the magnetic field and the quantum well width for the various exciton and magnetic states, and the variational calculation carried out in the adiabatic approach has shown the sizeable enhancement of the binding energy with increase of the external field.
Abstract: The exciton binding energy have been calculated as function of the magnetic field and the quantum well width for the various exciton and magnetic states. The variational calculation carried out in the adiabatic approach has shown the sizeable enhancement of the exciton binding energy with increase of the external field. For rather strong magnetic fields the exciton binding energy has been found in a framework of the perturbation theory. The results were used for the analysis of the spectra of light transmission through the thin semiconductor film containing GaAs/Al0.3Ga0.7As multiple quantum well structures and InxGa1-xAs/GaAs strained multiple quantum well structures in the external magnetic field tuning from 0 to 7.5 T at T equals 2 K.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: Using Lee-Low-Pines transformation and perturbative variational method, the effects of electron-phonon interaction on the exciton binding energy in a Ga1−xAlxAs quantum well can be solved analytically.
Abstract: Using Lee-Low-Pines transformation and perturbative variational method, the effects of electron-phonon interaction on the exciton binding energy in a Ga1−xAlxAs quantum well can be solved analytically. Our results show that the phonon effect on binding energy of heavy-hole exciton is always larger than that of light-hole exciton and the correction of polaron effect on the exciton binding energy in a quantum well cannot be neglected.
30 Oct 1995
TL;DR: In this paper, a formation technique of nanometer grains of Si and CoSi/sub 2/ embedded in a metal or semiconductor quantum box embedded in insulator barriers is investigated.
Abstract: Metal-insulator (M-I) superlattice is very attractive for ultra-fine, multifunctional and ultrahigh-speed quantum-effect electron devices because of the high carrier density of metal, low dielectric constant of insulator, and remarkable quantum-effect due to very large conduction-band discontinuity (>10 eV) at an M-I heterointerface. And moreover, optical devices using the same material system (metal-insulator and semiconductor heterostructure) is considered to be possible utilizing the optical transition between quantized energy levels in metal or semiconductor quantum wells or boxes embedded in insulator. In order to expand our study to 3-dimensional quantum confinement effect devices using CaF/sub 2/-CoSi/sub 2/-Si(111) material system, we have investigated a formation technique of nanometer grains of Si and CoSi/sub 2/ embedded in CaF/sub 2/. In a metal or semiconductor quantum box embedded in insulator barriers a strong 3-dimensional quantum confinement effect can be expected.