Stripe Contact Research Articles

Measurement methods and fractal dimensions of blast-cleaned steel substrates

ABSTRACT Morphological parameters of steel substrates determine the adhesion of coatings and adhesives. Three different assessment methods (cross section image, contact stylus instrument, and stripe light projection) were applied to blast-cleaned substrates. A total of 12 surface configurations were generated with different abrasive materials. The fractal dimensions were estimated by means of the box-counting method. Design of experiment and ANOVA were applied to statistically analyze the relationships. Factors included abrasive type, surface preparation grade, surface roughness, and surface profile measurement method. Similar relative trends for the fractal dimensions resulted for the three measurement methods. The normalized values of the fractal dimensions were approximately twice as high for the cross section profiles compared to the ones from contact stylus and stripe light projection. Fractal values derived from contact stylus measurements showed the highest repeatability, whereas those derived from cross section images showed the lowest repeatability.

Unexpected Electron Transport Suppression in a Heterostructured Graphene-MoS2 Multiple Field-Effect Transistor Architecture.

We demonstrate a graphene–MoS2 architecture integrating multiple field-effect transistors (FETs), and we independently probe and correlate the conducting properties of van der Waals coupled graphene–MoS2 contacts with those of the MoS2 channels. Devices are fabricated starting from high-quality single-crystal monolayers grown by chemical vapor deposition. The heterojunction was investigated by scanning Raman and photoluminescence spectroscopies. Moreover, transconductance curves of MoS2 are compared with the current–voltage characteristics of graphene contact stripes, revealing a significant suppression of transport on the n-side of the transconductance curve. On the basis of ab initio modeling, the effect is understood in terms of trapping by sulfur vacancies, which counterintuitively depends on the field effect, even though the graphene contact layer is positioned between the backgate and the MoS2 channel.

High-power AlGaInAs/InP semiconductor lasers with an ultra-narrow waveguide emitting in the spectral range 1.9−2.0 μm

High-power semiconductor lasers based on AlGaInAs/InP heterostructures and emitting in the spectral range 1.9−2.0 μm are developed. Strain compensation in the active region makes it possible to use InGaAs quantum wells with a compressive strain of about 2.0 %−2.5 %. The operation of a laser with an ultra-narrow waveguide at wavelengths increasing from 1.4−1.6 to 2.0 μm is studied. At room temperature, the semiconductor lasers with a stripe contact width of 100 μm demonstrates a cw output optical power of 1.0 W with a wavelength of 1.91 μm at a pump current of 6.5 A and with a wavelength of 1.98 μm at a pump current of 7.2 A.

Comparison of AlGaInAs/InP semiconductor lasers (λ = 1450 – 1500 nm) with ultra-narrow and strongly asymmetric waveguides

Semiconductor lasers based on AlGaInAs/InP heterostructures with ultra-narrow and asymmetric waveguides are comparatively studied. It is shown that the use of these waveguides with a simultaneous increase in the quantum well depth makes it possible to increase output powers. Such lasers based on both strongly asymmetric and ultra-narrow waveguides with a stripe contact width of 100 μm demonstrate an output power of 5 W (at pump currents of 11.5 and 14 A, respectively) in a continuous-wave regime at room temperature and a wavelength of 1450 – 1500 nm.

Semiconductor AlGaInAs/InP lasers (λ = 1450 – 1500 nm) with a strongly asymmetric waveguide

Semiconductor lasers based on AlGaInAs/InP heterostructures with a strongly asymmetric waveguide are studied. It is shown that the use of such a waveguide simultaneously with an increased quantum well energy depth provides conditions for increasing the output laser power. The semiconductor AlGaInAs/InP lasers based on a strongly asymmetric waveguide with a stripe contact width of 100 μm demonstrated an output optical power of 5 W (pump current 11.5 A) in a continuous-wave regime and 19 W (100 A) in a pulsed regime (100 ns, 1 kHz) at a wavelength of 1450 – 1500 nm at room temperature. The obtained data are compared with the output characteristics of lasers based on a symmetric waveguide.

AlGaInAs/InP semiconductor lasers with an ultra-narrow waveguide and an increased electron barrier

Semiconductor lasers based on AlGaInAs/InP heterostructures with an ultra-narrow waveguide and an increased electron barrier layer are developed. It is shown that the use of this waveguide in conjunction with profiled doping ensures a balance between internal optical losses and heat resistance. Additional use of strained wide-bandgap layers as blocking barriers limiting electron leakage from the active region makes it possible to increase the output power at the same pump current. The developed lasers with a stripe contact 100 μm wide demonstrate at room temperature an output optical power of 4.0 – 4.4 W (pump current 14 A) in a continuous-wave regime and 15 – 17 W (100 A) in a pulsed regime (100 ns, 1 kHz) at wavelengths of 1450 – 1500 nm.

Virtual cavity in distributed Bragg reflectors.

We show theoretically and experimentally that distributed Bragg reflector (DBR) supports a surface electromagnetic wave exhibiting evanescent decay in the air and oscillatory decay in the DBR. The wave exists in TM polarization only. The field extension in the air may reach several wavelengths of light. Once gain medium is introduced into the DBR a novel class of diode lasers, semiconductor optical amplifiers, light-emitting diodes, etc. can be developed allowing a new type of in-plane or near-field light outcoupling. To improve the wavelength stability of the laser diode, a resonant cavity structure can be coupled to the DBR, allowing a coupled state of the cavity mode and the near-field mode. A GaAlAs-based epitaxial structure of a vertical-cavity surface-emitting laser (VCSEL) having an antiwaveguiding cavity and multiple GaInAs quantum wells as an active region was grown and processed as an in-plane Fabry-Pérot resonator with cleaved facets. Windows in the top stripe contact were made to facilitate monitoring of the optical modes. Three types of the optical modes were observed in electroluminescence (EL) studies under high current densities > 1 kA/cm2. Mode A with the longest wavelength is a VCSEL-like mode emitting normal to the surface. Mode B has a shorter wavelength, emitting light at two symmetric lobes tilted with respect to the normal to the surface in the direction parallel to the stripe. Mode C has the shortest wavelength and shifts with a temperature at a rate 0.06 nm/K. Polarization studies reveal predominantly TE emission for modes A and B and purely TM for mode C in agreement with the theory. Spectral position, thermal shift and polarization of mode C confirm it to be a coupled state of the cavity mode and near-field DBR surface-trapped mode.

DFB Laser Diodes Based on GaN Using 10th Order Laterally Coupled Surface Gratings

Single longitudinal mode emission of laterally coupled distributed-feedback (LC-DFB) laser diodes (LDs) based on InGaN/GaN multiquantum-well structures containing 10th-order surface Bragg gratings with V-shaped grooves is demonstrated. The gratings were fabricated alongside a 2-μm-wide contact stripe by i-line stepper lithography and inductively coupled plasma etching. A single peak emission at 404.6 nm with a fullwidth at half-maximum of 0.04 nm was achieved at an output power of about 46 mW under pulsed laser operation. The shift of the lasing wavelength of LC-DFB LDs in the temperature range from 22 °C to 45 °C was around three times smaller than that of comparable ridge waveguide Fabry-Perot LDs.

DFB lasers with apodized surface gratings for wavelength stabilization and high efficiency

We present results of GaAs-based distributed-feedback (DFB) broad-area (BA) lasers with integrated surface-etched gratings. Lasers with longitudinally varying (apodized) Bragg gratings are compared to lasers with uniform gratings. DFB-BA lasers with apodized gratings show improved conversion efficiency and output power compared to those with uniform gratings. DFB-BA lasers with narrow contact stripe width W = 30 μm and resonator length L = 6 mm show a peak conversion efficiency of 60% and maintain efficiency >50% to an output power of >6 W. The spectral FWHM linewidth is below 0.5 nm. Furthermore DFB lasers with implemented apodized gratings are less sensitive to fabrication tolerances.

Technology of Producing the Contact Connections of Superconductor Metal-Sheathed Cable

Abstract The technology of producing the current contact connections on the superconductor cable edges is presented. This lead cable is used as one of the major elements of the magnetic system in thermonuclear reactor construction, actuality for modern world energy. The technology is realized by the radial draft of metal thin-walled tube on the conductor’s package. The filling of various profiles by round section wire is optimized. Geometrical characteristics of the dangerous crosssection (as a broken ring) of thin-walled tube injured by the sector cut-out are accounted. The comparative strength calculation of the solid and injured tubes at a longitudinal compression and lateral bending is acted. The radial draft mechanism of cylindrical thin-walled sheath with the wire packing is designed. The necessity to use the nonlinear theory for the sheaths calculate is set. The resilient co-operation of wires as the parallel located cylinders with the contact stripes of rectangular form is considered.

Semiconductor AlGaInAs/InP lasers with ultra-narrow waveguides

Laser diodes based on AlGaInAs/InP heterostructures with an ultra-narrow waveguide are developed. It is shown that the use of this waveguide in conjunction with profiled doping ensures a balance between internal optical losses and heat resistance. Laser diodes with a stripe contact 100 μm wide demonstrate at room temperature an output optical power exceeding 4 W in a continuous-wave mode and exceeding 20 W in a pulsed mode.

Generation of nanosecond and subnanosecond laser pulses by AlGaAs/GaAs laser-thyristor with narrow mesa stripe contact.

Lasers-thyristors with a narrow (20 μm) mesa stripe contact have been studied. It was shown that the laser peak power reaches a value of 2.5 W in the long-pulse mode at a pulse width of 13 ns. It was demonstrated that generation of a controlled train of laser pulses with peak power of 1.6 W and width of 90 ps is possible in the short-pulse mode. The maximum value of the pulse repetition frequency was 470 kHz at the following working characteristics of the laser-thyristor: blocking voltage 5.8 V, control current pulse 25 mA. A number of specific features were observed in the short-pulse mode. It was found that the blocking voltage and amplitude of the control current pulse affect the lasing process. We observed that in short pulse mode the lasing spectra have a two-band structure and the lateral near field may degenerate into a single spot with size substantially smaller than the mesa stripe width. It was shown that the main reason for the observed specific features of lasing is the clearly pronounced effect of the spatial localization of the current.

980-nm, 15-W cw laser diodes on F-mount-type heat sinks

We have studied the key optical emission parameters of laser diodes (emission wavelength, ; stripe contact width, ) mounted directly on F- and C-mount-type copper heat sinks, without intermediate elements (submounts). When effectively cooled by a thermoelectric microcooler, the lasers on the F-mount operated stably at output powers up to . The lasers were tested for reliable operation at an output power of for , and no decrease in output power was detected to within measurement accuracy. The experimentally determined maximum total efficiency is 71.7 % and the efficiency at a nominal output power of is 61 %. We compare parameters of the laser diodes mounted on C- and F-mounts and discuss the advantages of the F-mounts.

Efficiency Potential of Rear Heterojunction Stripe Contacts Applied in Hybrid Silicon Wafer Solar Cells

A 2-D numerical analysis evaluating the silicon solar cell efficiency potential of rear-side heterojunction stripe contacts embedded in an AlOx/SiNx passivation stack is presented. Simulated implied efficiencies of correspondingly passivated wafers and device efficiencies of corresponding hybrid solar cells are stated and compared with more conventional solar cell device architectures (i.e., n-PERT and full-area hybrid heterojunction cells). One-dimensional (full-area) and 2-D (stripe contact) lifetime samples are investigated as experimental input for simulation calibration. The influence of the rear-contact area fraction and pitch on both surface recombination and series resistance are investigated. The solar cell efficiency potential (i.e., the implied efficiency) of rear heterojunction stripe contacts is calculated using measured and simulated effective carrier lifetime and series resistance data. For a given (measured) injection-dependent lifetime of the heterojunction and dielectric passivation layers used, the optimum contact geometry (contact area fraction and pitch) is predicted. Assuming either a 1-ms effective lifetime for an ideal a-Si:H(i)/μc-Si:H(p) repassivated lifetime sample (i.e., assuming no laser-induced Si crystal damage due to the contact opening process) or an experimentally observed 300-μs lifetime for an a-Si:H(i)/μc-Si:H(p) repassivated lifetime sample, the calculated 1-sun efficiency potential of rear heterojunction stripe contacts (with optimized rear contact geometry) is 25.8% and 22.9%, respectively. The simulated efficiencies of corresponding hybrid heterojunction cells (having a conventional diffused front-contact system) are 22.7% and 21.4%, respectively. This is significantly higher than the calculated efficiency potential of more conventional solar cell architectures, such as n-PERT cells (20.6%) and full-area hybrid heterojunction solar cells (20.7%).

Effect of laser cavity parameters on saturation of light – current characteristics of high-power pulsed lasers

We report an experimental study of power characteristics of semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures with a broadened waveguide as functions of cavity length, stripe contact width and mirror reflectivities. It is shown that at high current pump levels, the variation of the cavity parameters of a semiconductor laser (width, length and mirror reflectivities) influences the light – current characteristic saturation and maximum optical power by affecting such laser characteristics, as the current density and the optical output loss. A model is elaborated and an optical power of semiconductor lasers is calculated by taking into account the dependence of the internal optical loss on pump current density and concentration distribution of charge carriers and photons along the cavity axis of the cavity. It is found that only introduction of the dependence of the internal optical loss on pump current density to the calculation model provides a good agreement between experimental and calculated characteristics for all scenarios of variations in the laser cavity parameters.

Thermal condition of high-power laser diodes

Light-current and current-voltage characteristics of a set of high-power laser diodes of the spectral region of 980 nm, fabricated by the authors, are experimentally studied. The dependences of their total efficiency and heat load on the pump current are constructed. The latter experimental dependence is used for calculations in the three-dimensional thermal model of the laser diode with a stripe contact width of 100 µm. Thermal fields are studied and isothermal surfaces are constructed for laser diodes fabricated on C-mount heat sink elements under heat loads corresponding to output powers of 10 W and higher in continuous mode.

Thermal modelling of high-power laser diodes mounted using various types of submounts

Using three-dimensional thermal modelling of a high-power laser diode with a stripe contact width of as an example, we analyse the thermal parameters of high-power laser diodes mounted using submounts. We consider a range of thermal conductivities of submounts that includes parameters of widely used thermal compensators based on AlN, BeO and SiC, as well as on CuW and CuMo composites and polycrystalline and single-crystal synthetic diamond with high thermal conductivity. Taking into account experimental overall efficiency vs. pump current data, we calculate the temperature of the active layer as a function of the width, thickness and thermal conductivity of the submount at thermal loads corresponding to cw output powers of 10, 15 and .

Emission parameters and thermal management of single high-power laser diodes

We report emission parameters of high-power cw laser diodes (LDs) with a stripe contact width of . On copper heat sinks of the C-mount type, a reliable output power of is obtained at a pump current of . Using a heat flow model derived from analysis of calculated and measured overall efficiencies at pump currents up to , we examine the possibility of raising the reliable power limit of a modified high-power LD mounted on heat sinks of the F-mount type using submounts with optimised geometric parameters and high thermal conductivity. The possibility of increasing the maximum reliable cw output power to with the use of similar laser crystals is discussed.

A novel total hip resurfacing design with improved range of motion and edge-load contact stress

A new hip resurfacing prosthesis design was assessed and compared in terms of kinematics and contact stress regarding to the conventional hip resurfacing prosthesis. For this purpose both designs were virtually implanted in a cadaveric computer-aided design model. Commercial software was employed to simulate the movements of flexion, abduction and internal rotation at 90° of flexion to determinate the impingement between femoral neck and acetabular cup. On the other hand, the edge load effect as consequence of different acetabular component inclinations and micro-separations were analyzed by finite element analysis for both designs. In addition, this effect was validated in the hip joint simulator FIME II. The results of the new design exhibited a significant motion increment before impingement of 12.8°±1.3° for flexion, 13.3°±3.1° for extension, 7.8°±1.9° for abduction and 13.1°±3.2° for internal rotation. Moreover, the new design showed a reduction of the contact stress and stripe wear during the running-in due to the micro-separation effect.

Degradation of high-power semiconductor quantum-well lasers

A mechanism of degradation of semiconductor quantum-well lasers with a stripe contact more than 50 µm wide is proposed. This mechanism implies formation of several lasing channels at a carrier ambipolar diffusion length smaller than the contact width. The carrier diffusion length decreases with time due to the increase in the number of defects; as a result, the number of lasing channels increases and lasing spectrum is filled. The shape of the lasing spectrum can be used to predict the laser service life.