Influence of growth parameters of frequency-radio plasma nitrogen source on extending emission wavelengths from 1.31 mu m to 1.55 mu m GaInNAs/GaAs quantum wells grown by molecular-beam epitaxy

High (42.5%) indium content GaInNAs/GaAs quantum wells with room temperature emission wavelength from 1.3 mu m to 1.5 mu m range were successfully grown by Radio Frequency Plasma Nitrogen source assisted Molecular Beam Epitaxy. The growth parameters of plasma power and N-2 How rate were optimized systematically to improve the material quality. Photoluminescence and transmission electron microscopy measurements showed that the optical and crystal quality of the 1.54 mu m GaInNAs/GaAs QWs was kept as comparable as that in 1.31 mu m.

The dependence of growth rate of GaN buffer layer on growth parameters by metalorganic vapor-phase epitaxy

The growth rate of GaN buffer layers on sapphire grown by metalorganic vapor-phase epitaxy (MOVPE) in an atmospheric pressure, two-channel reactor was studied. The growth rate, as measured using laser reflectance, was found to be dependent on growth temperature, molar flow rate of the sources tin this case, trimethylgallium and ammonia) and the input configuration of sources into the reactor. A model of the GaN buffer layer growth process by MOVPE is proposed to interpret the experimental evidence. (C) 1998 Elsevier Science B.V. All rights reserved.

Growth, characterization and optical quality of CaF2 single crystals grown by the temperature gradient technique

The CaF2 single crystals with diameters up to 200 mm were successfully grown by modified temperature gradient technique (TGT), which are suitable for application as optical elements in the ultraviolet range. The optimizations of various growth parameters were systematically studied. Properties of as-grown CaF2 crystals were characterized by the nature of inclusions, dislocations, crystallinity, and impurities contents. The results showed that the dislocations and multinucleation were mostly constrained in the conical part of the crystals with the cylindrical parts having the best crystalline quality and lowest impurity contents. The high optical quality of TGT-grown CaF2 single crystals was also confirmed to have excellent optical transmission in 190-2500 nm and refractive index homogeneity. (c) 2005 Elsevier Ltd. All rights reserved.

Czochralski growth and crystal structure of cerium-doped Lu2Si2O7 scintillator

Cerium-doped lutetium pyrosilicate crystal, Ce:Lu2Si2O7 (Ce:LPS), was grown by the Czochralski method. The segregation coefficient of Ce3+ ion was studied by the ICP-AES method. X-ray diffraction analysis showed that the structure of Ce:LPS crystal was monoclinic symmetry with space group of C2/m. Perfect cleavage planes (110) and imperfect cleavage planes (001) were observed by optical microscope. The reasons why it is difficult to grow crack-free crystals were studied. After optimized growth parameters, a Ce:LPS crystal with dimension of Phi 25 x 30 mm was grown, which is colorless, high optical quality, cracking-free and no inclusions. The transmittance of Ce:LPS crystal from 380 to 800 nm is over 82% and there is no observable absorption. (c) 2005 Elsevier B.V. All rights reserved.

Age structure, growth and mortality estimates of an endemic Ptychobarbus dipogon (Regan, 1905) (Cyprinidae: Schizothoracinae) in the Lhasa River, Tibet

Ptychobarbus dipogon is an endemic fish in the Yarlung Tsangpo River, but its biology is poorly known. We sampled 582 specimens (total length, TL, between 70.6 and 593.0 mm) from April 2004 to August 2006 in the Lhasa River, Tibet. We estimated ages based on the counts of alternating opaque and translucent zones (annuli) in thin transverse sections of lapilli otoliths. Ages ranged from 1(+) to 23(+) years for males and 1(+) to 44(+) for females. The observed 44(+) years was the oldest reported for schizothoracine fishes. Females attained a larger size than males. The TL weight relationship was W=7.12 x 10(-6)TL(3.006) for combined sexes. The growth parameters fitted von Bertalanffy growth functions were L-infinity = 598.66 mm, k=0.0898 year(-1), t(0)=-0.7261 year and W-infinity = 1585.38 g for females and L-infinity = 494.23mm, k=0.1197 year(-1), t(0)=-0.7296 year and W-infinity = 904.88g for males. The longevities of 32.7 year for females and 24.3 year for males were similar to the observed ages. Using an empirical model we estimated the instantaneous rate of total mortality (Z) at 0.28 per year in the lower reaches. Z in the upper and middle stocks was close to the M because of unexploited or lightly exploited stock. Protracted longevity, slow growth, low natural mortality and large body size were typical characteristics of P. dipogon. The current declining trend of P. dipogon could be prevented by altering fishing regulations.

Age and growth of Schizothorax waltoni in the Yarlung Tsangpo River in Tibet, China

Age and growth were studied for Schizothorax waltoni in the middle reaches of the Yarlung Tsangpo River in Tibet, southwest of China, from April 2004 to September 2006. A total of 201 specimens were collected ranging from 110 to 580 mm in standard length (SL). In contrast to other otoliths, sectioned lapillus showed a clear pattern of alternating opaque and hyaline zones. Marginal increment analyses showed that the increments, each composed of one opaque and one hyaline zone, are deposited annually. Opaque edges were prevalent from May to August. The von Bertalanffy growth parameters based on sectioned otolith data were L (t) = 689.8{1 - exp[0.051 (t + 3.275)]} for males, and L (t) = 691.1{1 - exp[0.056 (t + 2.466)]} for females. The slow growth and long life indicate that S. waltoni is vulnerable to overfishing and that harvesting strategies for the species should be conservative.

Chronic effects of water-borne PFOS exposure on growth, survival and hepatotoxicity in zebrafish: A partial life-cycle test

Perfluorooctane sulfonate (PFOS) is widely distributed and persistent in the environment and wildlife. The main aim of this study was to investigate the impact of long-term exposure to low concentrations of PFOS in zebrafish. Zebrafish fry (F-0, 14d post-fertilization, dpf) were exposed via the water for 70d to 0 (control), 10, 50 and 250 mu g L-1 PFOS, followed by a further 30d to assess recovery in clean water. The effects on survival and growth parameters and liver histopathology were assessed. Although growth suppression (weight and length) was observed in fish treated with high concentrations PFOS during the exposure period, no mortality was observed throughout the 70d experiment. Embryos and larvae (F-1) derived from maternal exposure suffered malformation and mortality. Exposure to 50 and 250 mu g L-1 PFOS could inhibit the growth of the gonads (GSI) in the female zebrafish. Histopathological alterations, primary with lipid droplets accumulation, were most prominently seen in the liver of males and the changes were not reversible, even after the fish were allowed to recover for 30d in clean water. The triiodothyronine (T-3)) levels were not significantly changed in any of the exposure groups. Hepatic vitellogenin (VTG) gene expression was significantly up-regulated in both male and female zebrafish, but the sex ratio was not altered. The overall results suggested that lower concentrations of PFOS in maternal exposure could result in offspring deformation and mortality. (c) 2008 Elsevier Ltd. All rights reserved.

Growth Parameter Dependence of Structural Characterizations of Diluted Magnetic Semiconductor (Ga, Cr)As

We report the influence of growth parameters and post-growth annealing on the structural characterizations and magnetic properties of (Ga, Cr)As films. The crystalline quality and magnetic properties are sensitive to the growth conditions. The single-phase (Ga, Cr)As film with the Curie temperature of 10 K is synthesized at growth temperature T-s = 250 degrees C and with nominal Cr content x = 0.016. However, for the films with x > 0.02, the aggregation of Cr atoms is strongly enhanced as both T. and x increase, which not only brings strong compressive strain in the epilayer, but also roughens the surface. The origin of room-temperature ferromagnetism in (Ga, Cr)As films with nanoclusters is also discussed.

Controllable growth of semiconductor nanometer structures

Self-assembled quantum dots and wires were obtained in the InxGa1-xAs/GaAs and InAs/In0.52Al0.48As/InP systems, respectively, using molecular beam epitaxy (MBE). Uniformity in the distribution, density, and spatial ordering of the nanostructures can be controlled to some extent by adjusting and optimizing the MBE growth parameters. In addition, some interesting observation on the InAs wire alignment on InP(001) is discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.

Growth mode and strain evolution during InN growth on GaN(0001) by molecular-beam epitaxy

Epitaxial growth of InN on GaN(0001) by plasma-assisted molecular-beam epitaxy is investigated over a range of growth parameters including source flux and substrate temperature. Combining reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM), we establish a relationship between film growth mode and the deposition condition. Both two-dimensional (2D) and three-dimensional (3D) growth modes of the film are observed. For 2D growth, sustained RHEED intensity oscillations are recorded while STM reveals 2D nucleation islands. For 3D growth, less than three oscillation periods are observed indicating the Stranski-Krastanov (SK) growth mode of the film. Simultaneous measurements of (reciprocal) lattice constant by RHEED suggest a gradual relaxation of the strain in film, which commences during the first bilayer (BL) deposition and almost completes after 2-4 BLs. For SK growth, 3D islanding initiates after the strain has mostly been relieved, presumably by dislocations, so the islands are likely strain free. (C) 2002 American Institute of Physics.

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.

Growth Parameter Dependence of Structural Characterizations of Diluted Magnetic Semiconductor (Ga, Cr)As

We report the influence of growth parameters and post-growth annealing on the structural characterizations and magnetic properties of (Ga, Cr)As films. The crystalline quality and magnetic properties are sensitive to the growth conditions. The single-phase (Ga, Cr)As film with the Curie temperature of 10 K is synthesized at growth temperature T-s = 250 degrees C and with nominal Cr content x = 0.016. However, for the films with x > 0.02, the aggregation of Cr atoms is strongly enhanced as both T. and x increase, which not only brings strong compressive strain in the epilayer, but also roughens the surface. The origin of room-temperature ferromagnetism in (Ga, Cr)As films with nanoclusters is also discussed.

MBE Growth of High Electron Mobility InP Epilayers

The molecular beam epitaxial growth of high quality epilayers on （100） InP substrate using a valve phosphorous cracker cell over a wide range of P/In BEP ratio （2.0-7.0） and growth rate （0.437 and 0. 791μm/h）. Experimental results show that electrical properties exhibit a pronounced dependence on growth parameters,which are growth rate, P/In BEP ratio, cracker zone temperature, and growth temperature. The parameters have been optimized carefully via the results of Hall measurements. For a typical sample, 77K electron mobility of 4.57 × 10^4 cm^2/（V · s） and electron concentration of 1.55×10^15 cm^-3 have been achieved with an epilayer thickness of 2.35μm at a growth temperature of 370℃ by using a cracking zone temperature of 850℃.

Metal-organic Vapor Phase Epitaxy Growth and Characterization of InAlGaN Epilayers

In order to improve crystal quality for growth of quaternary InAlGaN, a series of InAlGaN films were grown on GaN buffer layer under different growth temperatures and carrier gases by low-pressure metal-organic vapor phase epitaxy. Energy dispersive spectroscopy (EDS) was employed to measure the chemical composition of the quaternary, high resolution X-ray diffraction (HRXRD) and photoluminescence (PL) technique were used to characterize structural and optical properties of the epilayers, respectively. The PL spectra of InAlGaN show with and without the broad-deep level emission when only N2 and a N2+H2 mixture were used as carrier gas, respectively. At pressure of 1.01×104 Pa and with mixed gases of nitrogen and hydrogen as carrier gas, different alloy compositions of the films were obtained by changing the growth temperature while keeping the fluxes of precursors of indium (In), aluminum (Al), gallium (Ga) and nitrogen (N2) constant. A combination of HRXRD and PL measurements enable us to explore the relative optimum growth parameters-growth temperature between 850℃ and 870℃,using mixed gas of N2+H2 as carrier gas.

Controllable growth of semiconductor nanometer structures

Self-assembled quantum dots and wires were obtained in the InxGa1-xAs/GaAs and InAs/In0.52Al0.48As/InP systems, respectively, using molecular beam epitaxy (MBE). Uniformity in the distribution, density, and spatial ordering of the nanostructures can be controlled to some extent by adjusting and optimizing the MBE growth parameters. In addition, some interesting observation on the InAs wire alignment on InP(001) is discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.