Blue-green Light Emission Research Articles

Fabrication of multiperiod Si/SiO2/Ge layered structure through chemical bond manipulation

In this letter, we report a method called chemical bond manipulation for fabrication of multiperiod nanometer sized Si/SiO2/Ge layered structure. Chemical bond manipulation is a self-organization process which involves selective breaking and making of surface chemical bonds and thereby enable formation of the desired species on a full wafer scale. We show that oxygen of germanium oxide layer formed on Si(111) are picked up by the Si atoms arriving at the surface during subsequent growth. This phenomenon involves breaking of Ge–O bonds and making of Si–O bonds and leads to the formation of ultrathin Si and Ge layers sandwiched between ultrathin silicon oxide layers, preserving the original wafer morphology. This material exhibits blue-green light emission at room temperature when excited by ultraviolet laser.

Optically Stimulated Luminescence Radiation Dosimetry Using Doped Silica Glass

Optically stimulated luminescence is reported from novel transparent glass phosphors that were previously exposed to 60 Co γ radiation. Emission of blue-green light from the glass is stimulated by near-infrared light from a low power diode laser. Optically stimulated luminescence dosimetry measurements using the glass phosphors exhibit a linear exposure response from 2.58 μC.kg -1 to 12.9 C.kg -1 (10 mR to 50 kR). Optical stimulation with pulsed laser light provides the ability to perform multiple readouts of the exposure.

Optical spectroscopy in (Zn,Cd)Se-ZnSe graded-index separate-confinement heterostructures.

We report a detailed examination of the electronic structure and of the thermal transport in a graded-index separate-confinement heterostructure based on (Zn,Cd)Se wide-band-gap II-VI semiconductors, and designed in the view of a blue-green light emission device. The band offsets and strain state of the heterostructure are obtained from 2-K photoreflectance measurements. The temperature dependence of the photoluminescence spectra taken both in a resonant in-well excitation condition and in an above-barrier excitation condition has enabled us to quantify the mechanisms responsible for the photoluminescence thermal quenching. This has been done in the context of a sophisticated model that includes several nonradiative processes. In the 10--70 K temperature range, the photoluminescence intensity is found to be ruled by a nonradiative detrapping towards interfacial defects, whilst the thermal escape effect is responsible for the photoluminescence quenching at higher temperatures. In the case of an above barrier excitation condition, the contribution of the carriers diffusion from the barriers to the well leads to an increase of the quantum-well photoluminescence, the intensity of which exhibits a maximum around 50 K. \textcopyright{} 1996 The American Physical Society.

Recent progress in quantum structure materials, physics and devices

Recent studies on the electronic properties of semiconductor quantum structures have led to progress being made in areas such as Bloch oscillations, photon-assisted tunneling, quantum cascade lasers, blue-green light emitters, and microcavity effects. In addition, new epitaxial methods to prepare 10 nm scale quantum wires and dots have been found and greater insight into their unique properties attained.

Chemical sensitivity of convergent beam electron diffraction on the stoichiometry of GaN

III-V nitride thin film growth has attracted considerable attention because it now seems feasible to engineer semiconductor band gaps between 2.1 and 6.2 eV. One of the challenges coming with this development is related to the fact that structural perfection seems not to correlate directly with optical properties such as the emission of blue-green or UV light in GaN. In order to better understand this material High Resolution Transmission Electron Microscopy (HREM) and Convergent Beam Electron Diffraction (CBED) experiments were used to study structural defects in GaN thin films. Experiments were performed with a Topcon 002B and ARM operating at 200 and 800 KeV, respectively, and were guided by image simulations. Results of parallel luminescence studies will be published elsewhere.Plan-view micrographs of GaN grown on the (0001) basal plane of A12O3 with a lattice mismatch of 14% show small angle grain boundaries which divide the layer into large subgrains of about 800 nm diameter. Other defects visible in the plan-view micrographs are threading dislocations and planar defects lying parallel to the {1010} planes of the GaN.

Operation of strained-layer (In,Ga)As quantum welllasersprepared on (112)B GaAs substrate

The operation of (In,Ga)As quantum well lasers prepared on [112]-oriented GaAs substrates is reported. Threshold current densities as low as 187 A/cm2 for a 1.57 mm-long device have been obtained under pulsed-mode operation. The demonstration of laser action in a heterostructure grown on the [112]-oriented substrate is important for the design of blue-green light emitters.

Blue-green emitters in wide-gap II-VI quantum-confined structures

The physical features and practical challenges for wide bandgap II-VI semiconductor blue-green light emitters, both LED's and diode lasers, are reviewed in this rapidly moving field. Fundamental issues of optical and transport phenomena in the polar ZnSe-based compounds are examined, together with their impact on expected device performance. Examples of current device performance in the quantum well emitters are given, which have culminated in the recent demonstration of a room temperature CW diode laser. >

Degradation of II-VI based blue-green light emitters

We have carried out the first detailed structural studies of degradation in II-VI blue-green light emitters. Electroluminescence and transmission electron microscopy studies carried out on light emitting diodes fabricated from quantum well laser structures and electroluminescence studies on stripe laser structures show that degradation occurs by the formation and propagation of crystal defects. The studies indicate that room temperature cw lasing in such structures is possibly prevented by the rapid formation of such defects at the high current densities required for lasing.

Large blue shift of light emitting porous silicon by boiling water treatment

A boiling water treatment of light emitting porous silicon can give rise to a large blue shift of its photoluminescence spectrum and meanwhile strengthen the skeleton of porous Si by filling up many pores with aqueous oxide. A stable blue-green light emission at the peak wavelength down to 500 nm is achieved. FTIR measurements show that the formation of Si dihydride on the sidewall surfaces of the Si rods is not responsible to the visible luminescence for the very thin Si wires.

Growth of MnS, Cd1-xMnxSe, and MnS1-xSex Films by Molecular Beam Epitaxy (MBE) and Elemental Vapor Transport Epitaxy (EVTE) Techniques

This work addressed the MBE and EVTE growth of wide band gap semiconductor materials such as MnSe, Cd1−xMnxSe, and MnS1−xSex which have potential application for blue-green light emitters. It is the first time that EVTE was applied for high (Se, S, Cd) and low (Mn) vapor pressure materials, which required modification of the conventional design. The films were grown on GaAs 20 off (100) substrates and characterized using optical microscopy, SEM, EDS, X-ray, SIMS, Hall, and sheet resistance measurements. The deposition process parameters will be reviewed and related to results such as film composition, surface morphology, uniformity, and crystallinity. We report on growth of Cd1−xMnxSe with 0.42<X<0.99 and MnS1−xSex with 0.58<X<0.67. Different methods of controling elemental composition will be discussed. Grown materials show good surface morphlogy and uniformity. SIMS analysis demonstrated stable elemental composition throughout the film thickness and a sharp interface with the substrate.

Blue Light Emission from Porous Silicon

ABSTRACTThrough a post treatment of light emitting porous silicon in boilingwater, a large blue shift of its photoluminescence (PL) spectrum hasbeen observed and a stable blue-green light emission at the peak wavelength down to 500 nm is achieved. The effect of boiling water treatment is suggested to be a kind of oxidation, which could reduce thesize of the Si column, fill up some micropores and strengthen the Siskeleton. The photoluminescence microscopic observation shows that the surface of blue light emitting porous silicon is composed of manysmall uniformly light-emitting domains at the size of several tens of μm. Fourier transform infrared reflection (FTIR) measurements show that the formation of Si-H bonds is not responsible for the visible luminescence in the very thin Si wires.

The growth of ZnSe and other wide-bandgap II-VI semiconductors by MOCVD

ZnSe was first grown by MOCVD some years ago. However, it is only in recent years that the material quality has improved sufficiently for potential devices to be evaluated. This paper discusses the growth by MOCVD of high-purity ZnSe epitaxial layers, wide-bandgap II-VI ternary alloys, multilayers and low-dimensional structures with potential for blue or blue-green light emission. The growth conditions for high-purity ZnSe layers (ND-NA<1015 cm-3), the structure of such layers grown heteroepitaxially on to III-V semiconductor substrates, the influence of the precursors and the resulting luminescence are considered. Important factors such as the growth conditions required for the alloys and multilayers are also discussed, together with pertinent imposed material constraints. Finally, the major residual problems associated with MOCVD growth are identified and possible solutions presented.

Purification of the yellow fluorescent protein from vibrio fischeri and identity of the flavin chromophore

A low molecular weight protein (∼ 25,000 D) exhibiting a yellow fluorescence emission peaking at ∼ 540 nm was isolated from Vibrio fischeri (strain Y-1) and purified to apparent homogeneity. FMN is the chromophore, but it exhibits marked red shifts in both the absorption (λ max = 380, 460 nm) and the fluorescence emission. When added to purified luciferase from the same strain, which itself catalyzes an emission of blue-green light (λ max ∼ 495 nm), this protein induces a bright yellow luminescence (λ max ∼ 540 nm); this corresponds to the emission of the Y-1 strain in vivo . This yellow bioluminescence emission is thus ascribed to the interaction of these two proteins, and to the excitation of the singlet FMN bound to this fluorescent protein.