Green-light-emitting ZnSe nanowires fabricated via vapor phase growth

Stoichiometric ZnSe nanowires have been synthesized through a vapor phase reaction of zinc and selenium powder on the (100) silicon substrate coated with a gold film of 2 nm in thickness. The microstructures and the chemical compositions of the as-grown nanowires have been investigated by means of electron microscopy, the energy dispersive spectroscopy, and Raman spectroscopy. The results reveal that the as-grown materials consist of ZnSe nanowires with diameters ranging from 5 to 50 nm. Photoluminescence of the sample demonstrates a strong green emission from room temperature down to 10 K. This is attributed to the recombination of electrons from conduction band to the medium deep Au acceptors. (C) 2003 American Institute of Physics.

Size limit and spontaneous emission factor for equilateral triangle semiconductor microlasers

The size of equilateral triangle resonator (ETR) needed for confining the fundamental mode is investigated by the total reflection condition of mode light rays and the FDTD numerical simulation. The confinement of the TM modes can be explained by the total reflection of mode light rays, and the confinement of the TE modes requires a larger ETR than the TM modes, which may be caused by excess scattering or radiation loss for the TE modes. With the multilayer staircase approximation, it is found that the spontaneous emission factor of the ETR lasers has the same form as that of strip waveguide lasers.

Violet/blue emission from hydrogenated amorphous carbon films deposited from energetic CH3+ ions and ion bombardment

Considering the complexity of the general plasma techniques, pure single CH3+ ion beams were selected for the deposition of hydrogenated amorphous (a) carbon films with various ion energies and temperatures. Photoluminescence (PL) measurements have been performed on the films and violet/blue emission has been observed. The violet/blue emission is attributed to the small size distribution of sp(2) clusters and is related to the intrinsic properties of CH3 terminals, which lead to a very high barrier for the photoexcited electrons. Ion bombardment plays an important role in the PL behavior. This would provide further insight into the growth dynamics of a-C:H films. (C) 2002 American Institute of Physics.

Bloch oscillation under a bichromatic laser: Dynamical delocalization and localization, persistent terahertz emission, and harmonics generation

A novel AC driving configuration is proposed for biased semiconductor superlattices, in which the THz driving is provided by an intense bichromatic cw laser in the visible light range. The frequency difference between two components of the laser is resonant with the Bloch oscillation. Thus, multi-photon processes mediated by the conduction (valence) band states lead to dynamical delocalization and localization of the valence (conduction) electrons, and to the formation and collapse of quasi-minibands. Thus, driven Bloch oscillators are predicted to generate persistent THz emission and harmonics of the dipole field, which are tolerant of the exciton and the relaxation effects.

Cubic-phase GaN light-emitting diodes

The feasibility of growing device-quality cubic GaN/GaAs(001) films by metal organic chemical vapor deposition has been demonstrated. The optical quality of the GaN films was characterized by room-temperature photoluminescence measurements, which shows a full width at half maximum of 46 meV. The structural quality of the films was investigated by transmission electron microscopy. There are submicron-size grains free from threading dislocations and stacking faults. More importantly, a cubic-phase GaN blue light-emitting diode has been fabricated. The device process, which is very simple and compatible with current GaAs technology, indicates a promising future for the blue light-emitting diode. (C) 1999 American Institute of Physics. [S0003-6951(99)01416-3].

Properties of GaN epilayers with various growth conditions grown by gas source molecular beam epitaxy

GaN epilayers on sapphire (0001) substrates were grown by the gas source molecular beam epitaxy (GSMBE) method using ammonia (NH,) gas as the nitrogen source. Properties of gallium nitride (GaN) epilayers grown under various growth conditions were investigated. The growth rate is up to 0.6 mu m/h in our experiments. Cathodoluminescence, photoluminescence and Hall measurements were used to characterize the films. It was shown that the growth parameters have a significant influence on the GaN properties. The yellow luminescence was enhanced at higher growth temperature. And a blue emission which maybe related to defects or impurity was observed. Although the emission at 3.31 eV can be suppressed by a low-temperature buffer layer, a high-quality GaN epilayer can be obtained without the buffer layer. (C) 1998 Elsevier Science B.V. All rights reserved.

Tuning of emission wavelength of InAs/GaAs quantum dots sandwiched by combination layers

We investigate about controlling of photoluminescence (PL) wavelengths of InAs/GaAs self-assembled quantum dots (QDs) sandwiched with combination strained-buffer layer (CSBL) and combination strained-reducing layer (CSRL). The emission peak position of QDs is red-shifted to 1.37 mu m. The density of the QDs is increased to 1.17x10(10) cm(-2). It is indicated that optical properties of QDs could be improved by optimizing of the buffer and covering layers for the QDs. These results may provide a new way to further developing GaAs-based 1.3 mu m light sources.

A silicon light emitting devices in standard CMOS technology

A silicon light emitting device is designed and simulated. It is fabricated in 0.6 mum standard CMOS technology. The device can give more than 1 muW optical power of visible light under reverse breakdown. The device can be turned on at a bias of 0.88 V and work in a large range of voltage: 1.0-6.0 V The external electrical-optical conversion efficiency is more than 10(-6). The optical spectrum of the device is between 540-650 nm, which have a clear peak near 580 nm. The emission mechanism can be explained by a hot carrier direct recombination model.

Improved electroluminescence from n-ZnO/AlN/p-GaN heterojunction light-emitting diodes

n-ZnO/p-GaN heterojunction light-emitting diodes with and without a sandwiched AlN layer were fabricated. The electroluminescence (EL) spectrum acquired from the n-ZnO/p-GaN displays broad emission at 650 nm originating from ZnO and weak emission at 440 nm from GaN, whereas the n-ZnO/AlN/p-GaN exhibits strong violet emission at 405 nm from ZnO without GaN emission. The EL intensity is greatly enhanced by inserting a thin AlN intermediate layer and it can be attributed to the suppressed formation of the GaOx interfacial layer and confinement effect rendered by the AlN potential barrier layer.

POLARIZATION OF HOT PHOTOLUMINESCENCE IN QUANTUM-WELLS AND HEAVY-LIGHT HOLE MIXING

Hot electrons excited from the valence band by linearly polarized laser light are characterized by certain angular distributions in momenta. Owing to such angular distributions in momenta, the photoluminescence from the hot electrons shows a certain degree of polarization. A theoretical treatment of this effect observed in the photoluminescence in quantum wells is given, showing that the effect depends strongly on heavy and light hole mixing. The very large disparity between the experimentally observed and theoretically expected values of the degree of polarization in the hot-electron photoluminescence suggests the presence of random quasielastic scattering. The effects of such additional scattering and the presence of a perpendicular magnetic field are incorporated into the theory. it is shown that the measurements of the degree of polarization observed in the hot electron photoluminescence, with and without an applied perpendicular magnetic field can serve to determine the time constants for both LO-phonon inelastic and random quasielastic scattering. As an example, these time constants are determined for the experiments reported in the literature.

Two-dimensional excitonic emission in InAs submonolayers

Photoluminescence (PL) and time-resolved photoluminescence (TRPL) were used to study optical emissions of ultrathin InAs layers with average layer thickness ranging from 1/12 to 1 ML grown on GaAs substrates. We have found that the inhomogeneous broadening of the PL from InAs layers can be well described by the quantum-well model with InAs islands coupling to each other and being regarded as a quasiwell. From the temperature dependence of the exciton linewidth, the exciton-LO-phonon scattering coefficient was found to be comparable to that in conventional two-dimensional quantum wells. In the TRPL measurements, the PL decay time increases linearly with temperature, which is a typical characteristic of free excitons in quantum wells. All these results indicate that the excitons localized in InAs exhibit two-dimensional properties of quantum wells, despite the topographical islandlike structure.

Stable Temperature Characteristics of InAs/GaAs Quantum Dots at Long Wavelength Emission

The time-resolved photoluminescence and steady photoluminescence (TRPL and PL) spectra on self-assembled InAs/GaAs quantum dots (QDs) are investigated. By depositing GaAs/InAs short period superlattices (SLs), 1. 48 μtm emission is obtained at room temperature. Temperature dependent PL measurements show that the PL intensity of the emission is very steady. It decays only to half as the temperature increases from 15 K to room temperature, while at the same time, the intensity of the other emission decreases by a factor of 5 orders of magnitude. These two emissions are attributed to large-size QDs and short period superlattices (SLs), respectively. Large-size QDs are easier to capture and confine carriers,which benefits the lifetime of PL, and therefore makes the emission intensity insensitive to the temperature.

Graded tensile-strained bulk InGaAs/InP superluminescent diode with very wide emission spectrum

A kind of novel broad-band superluminescent diodes (SLDs) using graded tensile-strained bulk InGaAs is developed. The graded tensile-strained bulk InGaAs is obtained by changing only group-III trimethyl-gallium source flow during low-pressure metal organic vapor-phase epitaxy. At the injection current of 200 mA, the fabricated SLDs with such structure demonstrate full-width at half-maximum spectral width of 106 nm and the output light power of 13.6 mW, respectively.

Potential light source for photonic integrated circuits based on the equilateral triangle resonator

The semiconductor microlasers based on the equilateral triangle resonator (ETR) can be fabricated from the edge-emitting laser wafer by dry-etching technique, and the directional emission can be obtained by connecting an output waveguide to one of the vertices of the ETR. We investigate the mode characteristics, especially the mode quality factor, for the ETR with imperfect vertices, which is inevitable in the real technique process. The numerical simulations show that the confined modes can still have a high quality factor in the ETR with imperfect vertices. We can expect that the microlasers is a suitable light source for photonic integrated circuits.

Photoluminescence measurements on erbium-doped silicon

Erbium-implanted silicones were treated by lamp-heating rapid thermal annealing (RTA). Two types of erbium-related photoluminescence spectra appear under different anneal temperatures. 750 degrees C annealing optimizes the luminescence intensity, which does not change with anneal time. Exciton-mediated energy transfer model in erbium-doped silicon was presented. The emission intensity is related to optical active erbium concentration, lifetime of excited Er3+ ion and spontaneous emission time. The thermal quenching of the erbium luminescence in Si is caused by thermal ionization of erbium-bound exciton complex and nonradiative energy backtransfer processes, which correspond to the activation energy of 6.6 meV and 47.4 meV respectively.