Fabrication and modulation characteristics of InGaAsP/InGaAsP MQW DCPBH lasers at λ ∼ 1.57 μm

InGaAsP/InGaAsP multiple-quantum-well (MQW) double-channel planar-buried heterostructure (DCPBH) lasers emitting at λ∼ 1.57 μm were fabricated by optimizing the epitaxial growth with material characterization. At 25 °C (85 °C), a 1.8-μm-wide and 300-μm-long antireflectivity/high reflectivity coated laser exhibits a threshold current of 8 mA (23 mA) and a slope efficiency of 0.34 mW/mA (0.24 mW/mA) in continuous-wave mode (cw) as a result of the optimized thickness of the p-InP filling layer in the PBH structure with p-n-p-n current blocking layers. The maximum cw output power was approximately 20 mW at 25 °C, which was reduced to 17 mW at 85 °C. The peak wavelength varied from 1572 nm at 25 °C to 1602 nm at 100 °C for a fixed output power of 5 mW, indicating a temperature coefficient of ∼ 0.4 nm/K. The resonance frequency in the small-signal modulation response of devices depends on the etching depth of the U-shaped double channel; it increases from 0.4 GHz without channel etching to 4.3 GHz with 7-μm-thick etching. The full-width at half maximum values in the horizontal and vertical far-field patterns were approximately 24.5° (25.2°) and 29.4° (30.1°), respectively, at 25 °C (85 °C). PACS 42.55.Px; 73.61.Ey; 81.05.Ea     

Nitriding of Stainless Steel in Electron-Beam Plasma in the Pulsed and DC Generation Modes

The influence of electron-beam parameters on the thickness and phase composition of a hardened layer formed upon the nitriding of austenitic stainless steel 12Cr18Ni10Ti in plasma produced by a beam in a low-pressure (3 Pa) nitrogen-argon mixture is studied. The results obtained in the DC and pulse-periodic modes of beam generation with the same mean current and electron energy are compared. In this case the negative bias voltage applied to the samples is 100 V. The nitriding temperature of 400°C is maintained at a mean beam current of 2.6 A and various combinations of frequency (100–500 Hz) and current pulse durations (0.1–0.3 ms) with an amplitude of 80 A. The mean ion-plasma current densities in the DC and pulsed modes are close in magnitude (2–3 mA/cm² at 400°C). The high pulsed ion-current density (35–70 mA/cm²) creates conditions under which the surface sputtering rate during the pulse exceeds the growth rate of the nitrided layer. The nitriding of steel in the pulsed and DC modes over four hours gives the same result. Hardened layers with a thickness of 7–8 μm and a microhardness of the surface component of 15 ± 1 GPa in which the main phase is a supersaturated nitrogen solid solution (expanded austenite) are formed. A possible explanation is that nitriding in an electron-beam plasma proceeds mainly under the action of long-lived active neutral nitrogen particles rather than as a result of ion bombardment.     

Properties of Eu-doped zinc oxide thin films grown on glass substrates by radio-frequency magnetron sputtering

Eu-doped ZnO (EZO) thin films were prepared on glass substrates at various growth temperatures by radio-frequency magnetron sputtering. The properties of deposited thin films showed a significant dependence on the growth temperature. The preferential growth orientation of all the thin films was occurred along the ZnO (002) plane. The maximum crystallite size and the minimum average transmittance in the wavelength range of 450–1100 nm were observed for the EZO thin film deposited at 25 °C. A red shift of the optical band gap was observed in the growth temperature range of 25–300 °C. The highest figure of merit, an index for evaluating the performance of transparent conducting thin films, was obtained at 200 °C of growth temperature. These results indicated that the high-quality EZO film was obtained at a growth temperature of 200 °C.     

Disorders produced during high-current and high-dose phosphorus ion implantation in silicon

Transmission electron microscopy, optical reflection and channeling effect measurements are employed to investigate disorders in 30 keV, high dose (3×10¹⁶ions/cm²) and high current (≦5 mA) phosphorus as-implanted silicon with (111), (100), and (110) orientation as a function of temperature rise (100–850°C) by the beam heating effect during implantation. Temperature rise below 400°C results in continuous amorrphous layer formation. This contrasts with results of the recovery into single crystals for temperature rise samples above 500°C, regardless of wafer orientation. Secondary defects (black-dotted defects, dislocation loops and rodlike defects) are formed in singlecrystal recovery samples, having a deeper distribution in (110) wafers and a shallower distribution in (111) and (100) wafers. Rodlike defects observed in 850°C samples are of “vacancy” type and have the largest density in (110) wafers.     

Thermal and optical properties of Cd2SnO4 thin films using photoacoustic spectroscopy

Cadmium stannate (Cd₂SnO₄) thin films were prepared by the RF magnetron sputtering technique on glass substrates with substrate temperatures of room temperature (RT), 100°C, 200°C and 300°C. Photoacoustic analyses were made to obtain the thermal diffusivity and the optical bandgap values of the Cd₂SnO₄ thin films. The change in thermal diffusivity of the films with the substrate temperature was analyzed. The optical bandgap values obtained from the photoacoustic spectroscopy were compared with the values obtained from the optical transmittance spectra. X-ray photoelectron spectroscopic (XPS) studies confirm the formation of stoichiometric films. Surface morphological studies by atomic force microscopy (AFM) revealed the crystalline nature of the films deposited at 100°C.     

Impact of growth temperature on the properties of SnS film prepared by thermal evaporation and its photovoltaic performance

Tin(II) sulfide (SnS) films are one of the most promising absorber materials for high efficiency solar cells without using rare metals. In this work, SnS films were deposited by the thermal evaporation on glass substrates under the variation of growth temperatures of 100–250 °C. It was revealed that the SnS thin film prepared under the temperature of 100 °C had relatively small crystal grains. On the other hand, the denser and larger crystal grains of the SnS films were obtained with the constant compositions, when the growth temperature increased to 225 °C. With the temperature of higher than 225 °C, the SnS began to be re-evaporated from the films. The highest Hall mobility of the films was obtained under the temperature of 200 °C. Ultimately, the results suggested that the optimized growth temperature of SnS by the evaporation is 200 °C, giving rise to compact and large crystal grains and the highest Hall mobility, thereby contributing to the 2.53%-efficient SnS thin-film solar cell.     

Fim observation of an iron deposited tungsten tip

An iron-deposited tungsten tip was observed with a field ion microscope. The observed features were classified into five types corresponding to the various substrate temperatures. Epitaxial growth was observed at substrate temperatures ranging from 100°C to 500°C, though the parallelism was not perfect. An epitaxially grown film was observed only on one side of a tip cap at a low temperature. The film spread to the entire tip cap at a higher temperature. Diffusivity of the deposited iron was estimated from the observed migration of the iron atoms. Images which implied the formation of an alloy of kon and tungsten were obtained at 550–660°C. When the substrate temperature exceeded 700°C, iron atoms were not observed on the tip cap. These sequential change corresponding to the substrate temperatures will be discussed in relation to the surface diffusion of the deposited iron and substrate tungsten atoms.     

Research of the use of silver nanowires as a current spreading layer on vertical-cavity surface-emitting lasers

Silver nanowire(AgNW) film was proposed to apply on the surface of the vertical-cavity surface-emitting lasers(VCSELs) with large aperture in order to obtain a uniform current distribution in the active region and a better optical beam quality.Optimization of the AgNW film was carried out with the sheet resistance of 28.4 Ω/sq and the optical transmission of 94.8% at 850 nm.The performance of VCSELs with and without AgNW film was studied.When the AgNW film was applied to the surface of VCSELs,due to its better current spreading effect,the maximum output optical power increased from 23.4 mW to 24.4 mW,the lasing wavelength redshift decreased from 0.085 nm/mA to 0.077 nm/mA,the differential resistance decreased from 23.95 Ω to 21.13 Ω,and the far field pattern at 50 mA decreased from 21.6° to 19.2°.At the same time,the near field test results showed that the light in the aperture was more uniform,and the far field exhibited a better single peak characteristic.Various results showed that VCSELs with AgNW on the surface showed better beam quality.     

Microstructure and electrochemical properties of porous La2NiO4+δ electrodes spin-coated on Ce0.8Sm0.2O1.9 electrolyte

Porous La₂NiO_4+?? electrodes were prepared from superfine starting powder on dense substrates of Ce_0.8Sm_0.2O_1.9 electrolyte by a spin coating technique. The microstructure and electrochemical properties of the electrodes were investigated within the sintering temperature range of 1,000?C1,100?°C. An obvious effect of sintering temperature on the microstructure and electrochemical properties was detected. The variation of the electrochemical properties with sintering temperature was explained in relation to the microstructural evolution of the porous electrodes. It was detected that the electrode processes greatly depended on the microstructure of the electrodes. The polarization of surface oxygen exchange process was found to be the major contribution to the total electrode polarization. The electrode sintered at 1,050?°C showed the optimum electrocatalytic activity among the investigated electrodes. At 800?°C, the electrode exhibited a polarization resistance of 0.42????cm², an overpotential of 48?mV at a current density of 200?mA?cm^?2 and an exchange current density of 121?mA?cm^?2.     

AlGaInP visible quantum well lasers for information technology

650 nm-range AlGaInP multi-quantum well (MQW) laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) have been studied and the results are presented in this paper. Threshold current density of broad area contact laser diodes can be as low as 350 A/cm². Laser diodes with buried-ridge strip waveguide structures were made, threshold currents and differential efficiencies are (22–40) mA and (0.2–0.7) mW/mA, respectively. Typical output power for the laser diodes is 5 mW, maximum output power of 15 mW has been obtained. Their operation temperature can be up to 90°C under power of 5 mW. After operating under 90°C and 5 mW for 72 hrs, the average increments for the threshold currents of the lasers at 25°C and the operation currents at 5 mW (at 25°C) are (2–3) mA and (3–5) mA, respectively. Reliability tests showed that no obvious degradation was observed after 1400 hours of CW operation under 50°C and 2.5 mW. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998.     

Study on Impact Property and Fracture Morphology of Injection-molded Optical-grade Polycarbonate

The low-velocity, low-energy impact response of optical-grade polycarbonate (PC) was characterized by the Izod impact testing at ambient temperature. The following factors affecting impact response were investigated: mold temperatures (80, 90, 100, 110, and 120°C) and annealing treatment (120°C for 12 h). The results showed that the annealing treatment remarkably reduced the impact strength. The maximum impact strength was obtained when the mold temperature was 100°C for both unannealed samples and annealed ones. Moreover, the annealing treatment changed the failure mode of specimens from ductile failure to brittle failure, which was confirmed by fracture morphology analysis using scanning electron microscopy (SEM). The ductile failure was attributed to shearing behavior, and the fracture surfaces were rough and irregular with many river-shaped striations. The brittle fracture was caused by a craze failure mechanism. The brittle fracture sections could be divided into three regions: fracture origin, mist region, and end-wall banded region.     

Atmospheric pressure chemical vapor deposition (APCVD) grown bi‐layer graphene transistor characteristics at high temperature

We report the characteristics of atmospheric chemical vapor deposition grown bilayer graphene transistors fabricated on ultra‐scaled (10 nm) high‐κ dielectric aluminum oxide (Al₂O₃) at elevated temperatures. We observed that the drive current increased by >400% as temperature increased from room temperature to 250 °C. Low gate leakage was maintained for prolonged exposure at 100 °C but increased significantly at temperatures >200 °C. These results provide important insights for considering chemical vapor deposition graphene on aluminum oxide for high temperature applications where low power and high frequency operation are required. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Austenite grain growth kinetics and mechanism of grain growth in 12Cr ultra-super-critical rotor steel

ABSTRACT

In this paper, the austenite grain growth behaviour of 12Cr ultra-super-critical (USC) rotor steel was investigated by a series of heat treatments. The heat treatments at heating temperatures of 900°C–1250°C and holding time of 1?h–20?h were conducted in an electric box-type heating furnace. Experimental results showed that the sizes of austenite grain were affected by heating temperatures and holding time, and heating temperature was the dominant factor. In addition, the grain growth rate changed significantly before and after the turning points of 1050°C and 1250°C. Meanwhile, an austenite grain growth mathematical model was established at different heating temperature stages, and possession of the capability to accurately predict austenite grain size was confirmed. Furthermore, the microstructure of austenite grain in the heating process was observed by optical microscope (OM) and transmission electron microscopy (TEM), which revealed the mechanism of austenite grain growth. Analysis indicated that the change of quantity of precipitate particles with increasing heating temperature was the main reason for the difference in austenite grain growth.     

Long wavelength strain-engineered InAs multi-layer stacks quantum dots laser diode on GaAs substrate

The growth of GaAs based 1.5 ??m multi-layer stacked InAs quantum dots (QDs) has been investigated by solid-source molecular beam epitaxy (SSMBE), which was very important devices for transmission window. Owing to a strong electronic coupling between the QDs layers and the quantum wells (QWs), and antimony (Sb) introduced by for long-wavelength semiconductor lasers were obtained. The device structure for QDs laser diodes (LDs) with a cavity length of 1000 ??m and stripe width of 100 ??m as well as the device fabrication results will also be presented. The output performance was achieved with continuous wave (CW) operation, the measurement were from 20 to 60°C with a temperature step of 10°C. The threshold current density was 168 A/cm², and the CW operating up to 20 mW at room temperature (RT) was achieved.     

Silver-induced activation for improving the electrical characteristics of GaN-based vertical light-emitting diodes

Silver (Ag) contacts are important reflectors for vertical-structure GaN-based light-emitting diodes (LEDs). The Ag contacts produce good electrical and optical properties at different annealing temperatures. Thus, in order to best optimize the reliability of LEDs, we introduced an Ag activation process before performing normal annealing treatments. In other words, after removing 200-nm-thick Ag layers on p-GaN that were annealed at 500 °C for 1 min, Ag films were deposited on the Ag-activated p-GaN, which were subsequently annealed at 300 °C for 1 min. The activated LEDs fabricated with the 300 °C-annealed Ag contacts reveal better electrical properties than the reference LEDs. For example, the activated LEDs give a forward voltage of 2.92 V at an injection current of 20 mA, whereas the reference LEDs with the 300- and 500 °C-annealed Ag contacts yield 3.02 and 2.98 V at 20 mA, respectively. The activated LEDs yield 4.9% and 17% higher output power (at 30 mW) than the reference LEDs with the Ag contacts annealed at 300 and 500 °C. The activation-induced electrical improvement is briefly described and discussed.     

Complete-single-mode operation of 180° mode phased array lasers by improving temperature distribution inside the stripe region

180° mode phased array lasers with multiple stripes were systematically investigated for high-power, single lateral mode operation. Phased array lasers with a conventional loss guide structure were fabricated for 180° mode operation because the structure allowed the threshold gain of 180° mode to become smallest by introducing optical loss between stripes and outside the stripe region. It showed complete single lateral mode operation under pulsed condition. However, under continuous wave operation, phase-uncoupling occurred at the edge emitters as a result of the temperature distribution inside the stripe region. This was confirmed both experimentally and theoretically. To minimise the temperature distribution, dummy stripes were introduced outside the stripe region. The current in the dummy stripes did not cause lasing, but did increase the temperature of the edge stripes, which improved the thermal distribution inside the stripe region. As a result, complete single lateral 180° mode operation under continuous wave operation was attained.     

Effects of preannealing temperature of ZnO thin films on the performance of dye-sensitized solar cells

The preferred (002) orientation zinc oxide (ZnO) nanocrystalline thin films have been deposited on FTO-coated glass substrates by sol–gel spin-coating technology and rapid thermal annealing for use in dye-sensitized solar cells (DSSC). The effects of preannealing temperature (100 and 300°C) on the microstructure, morphology and optical properties of ZnO thin films were studied. The ZnO thin films were characterized by X-ray diffraction (XRD), scanning electron microscopic (SEM) and Brunauer–Emmett–Teller (BET) analysis. The photoelectric performance of DSSC was studied by I–V curve and the incident photon-to-current conversion efficiency (IPCE), respectively. From the results, the intensities of (002) peaks of ZnO thin films increases with increasing preannealing temperature from 100°C to 300°C. The increase in pore size and surface area of ZnO films crystallized at the increased preannealing temperature contributed to the improvement on the absorption of N3 dye onto the films, the short-circuit photocurrent (J _sc) and open-circuit voltage (V _oc) of DSSC. The higher efficiency (η) of 2.5% with J _sc and V _oc of 8.2 mA/cm² and 0.64 V, respectively, was obtained by the ZnO film preannealed at 300°C.     

Ellipsometric studies of annealing of SiO2 layers during the formation of light-emitting Si nanocrystals in them

Annealing of SiO₂ layers with excessive Si leading to the formation of silicon nanocrystals capable of fluorescing in the visible region owing to quantum-dimensional limitations is studied by the ellipsometry method. Excessive Si was introduced in SiO₂ layers by ion implantation with an energy of 25 keV and a dose of 5× 10¹⁶ cm^?2. Isochronous (10³ s) annealings were carried out in a temperature interval of 200–1150°C with a step of 100°C. An LÉF-2 ellipsometer with a 70° angle of incidence at a wavelength of 632.8 nm was used for the measurements. Fluorescence excited by a nitrogen laser was monitored concurrently. It is found that variations in optical constants of the layers at each step of annealing over the entire temperature range studied are clearly detected by ellipsometry. Variations in optical parameters of excessive Si are calculated in the Bruggeman approximation. They are found to correspond to individual stages of the formation of nanoprecipitates revealed earlier by other techniques. Nanocrystals proper producing intense visible photoluminescence are formed at annealing temperatures of 1000°C and higher.     

Synthesis,deposition and characterization of tin selenide thin films by thermal evaporation technique

Tin selenide alloy was synthesized by following simple chemical reaction method, at comparatively lower temperature of 100 °C, from alkaline medium using SnCl₂.2H₂O and selenium as source materials. Powder X-ray diffraction analysis reveals that the particle size of the synthesized product is in nanometer scale. Using the reaction product as source material, the SnSe films were deposited on glass substrates at room temperature, 150 °C, 250 °C, 350 °C and 450 °C. Structural, elemental, optical, surface morphological and electrical properties of the as deposited films were studied by X-ray diffraction, Energy Dispersive X-ray Analysis, UV-Vis-NIR, Scanning Electron Microscopy and Hall effect measurement techniques and the relevant details have been obtained.     

Deformation mechanisms of ultra-thin Al layers in Al/SiC nanolaminates as a function of thickness and temperature

The mechanical properties of Al/SiC nanolaminates with layer thicknesses between 10 and 100 nm were studied by nanoindentation in the temperature range 25 to 100 °C. The strength of the Al layers as a function of the layer thickness and temperature was obtained from the hardness of the nanolaminates by an inverse methodology based on the numerical simulation of the nanoindentation tests by means of the finite element method. The room temperature yield stress of the Al layers showed a large ‘the thinner, the stronger’ effect, which depended not only on the layer thickness but also on the microstructure, which changed with the Al layer thickness. The yield stress of the Al layers at ambient temperature was compatible with a deformation mechanism controlled by the interaction of dislocations with grain boundaries for the thicker layers (>50 nm), while confined layer slip appeared to be dominant for layers below 50 nm. There was a dramatic reduction in the Al yield stress with temperature, which increased as the Al layer thickness decreased, and led to an inverse size effect at 100 °C. This behavior was compatible with plastic deformation mechanisms controlled by grain boundary and interface diffusion at 100 °C, which limit the strength of the ultra-thin Al layers.