Thermal resistance of InGaAs/InP laser diodes

Results of theoretical and experimental investigations of the thermal behaviour of InGa-AsP/InP laser diodes with a ridge-waveguide structure are presented. It is shown that, in contrast to GaAlAs/GaAs laser diodes, most of the heat flux is carried through the InP-substrate, less than 1/4 through the ridge. The temperature rise in the active region was determined and the thermal resistance calculated for various structure and bond parameters. The theoretical and experimental results fit very well. The change of the thermal resistance compared to a norm value of 67 K/W with variation of structure parameters is discussed. It is strongly affected by the device length, the ridge width and the bonding parameters.

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Zusammenfassung Die Ergebnisse einer theoretischen und experimentellen Untersuchung des thermischen Verhaltens von InGaAsP/InP Laserdioden mit Stegwellebleiterstruktur wurden dargelegt. Es wurde gezeigt, da\ der grö\te Teil des WÄrmeflusses durch das InP-Substrat geleitet wird, nur weniger als 1/4 durch den Steg. Man bestimmte den Temperaturanstieg in der aktiven Zone und berechnete für verschiedene Struktur- und Montageparameter die thermische Widerstand. Theoretische und experimentelle Ergebnisse stimmen gut miteinander überein. Die Änderung der thermischen BestÄndigkeit verglichen mit einem Normwert von 67 K/W wird in AbhÄngigkeit der Strukturparameter untersucht. Sie wird durch chiplÄnge Stegbreite und Bindungsparameter stark beeinflu\t.

     

Thermal conditions of growth and the necking evolution of Si,GaSb AND GaAs

The configuration of thermal gradient is illustrated for various types of crucible rotation, which is important for the creation of dislocations, which decreases along the grown axis of crystal. A new mechanism for dislocation elimination during the growth is proposed to explain this phenomenon, which provides a good agreement with the experimental results. The concentration of etch pits rapidly decreased from the beginning to the end of the crystals and the dislocation densities in the middle portion of all investigated crystals were found less than 102 cm^-2. The shallow vertical temperature gradients and virtually flat solidification interface prevented thermal stress from their building up in the crystals. As a result, the dislocation formation had random distribution. Using good necking procedures and choosing an appropriately oriented starting crystal with the shoulder angle <38.94° (assuming growth in <111> direction) it is possible to produce almost dislocation-free crystals without resorting to additional doping normally employed to reduce dislocation formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of thicknesses of InP epilayers on InP/GaAs heterostructure

InP epilayers with different thicknesses were grown on GaAs substrates at a low temperature by using metalorganic chemical vapor deposition. Atom force microscope and double‐crystal X‐ray were carried out to investigate the morphology and the crystal quality. Transmission electron microscopy was performed to characterize the microstructure and morphology. It was found that with the epilayer thicknesses increased, the crystal quality was improved and the dislocations in epilayers were decreased. Moreover, the sample that has 150‐nm InP epilayer could observe large numbers of antidislocations in the gallium arsenide substrate. The formation mechanism of antidislocations was also discussed with the analysis of crystal structure and surface morphology. Furthermore, we proposed a mechanism to explain the motion and the reaction of antidislocations.     

Block copolymer-templated chemistry on Si, Ge, InP, and GaAs surfaces

Patterning of semiconductor surfaces is an area of intense interest, not only for technological applications, such as molecular electronics, sensing, cellular recognition, and others, but also for fundamental understanding of surface reactivity, general control over surface properties, and development of new surface reactivity. In this communication, we describe the use of self-assembling block copolymers to direct semiconductor surface chemistry in a spatially defined manner, on the nanoscale. The proof-of-principle class of reactions evaluated here is galvanic displacement, in which a metal ion, M+, is reduced to M0 by the semiconductor, including Si, Ge, InP, and GaAs. The block copolymer chosen has a polypyridine block which binds to the metal ions and brings them into close proximity with the surface, at which point they undergo reaction; the pattern of resulting surface chemistry, therefore, mirrors the nanoscale structure of the parent block copolymer. This chemistry has the added advantage of forming metal nanostructures that result in an alloy or intermetallic at the interface, leading to strongly bound metal nanoparticles that may have interesting electronic properties. This approach has been shown to be very general, functioning on a variety of semiconductor substrates for both silver and gold deposition, and is being extended to organic and inorganic reactions on a variety of conducting, semiconducting, and insulating substrates.     

Multi-gas sensing based on photoacoustic spectroscopy using tunable laser diodes

Multi-hydrogenated compounds detection based on photoacoustic (PA) spectroscopy is reported. Three near-infrared semiconductor lasers are used with a resonant PA cell operated in its first longitudinal mode to monitor methane, water vapour and hydrogen chloride in the parts per million range. The design of our cell results from simulations performed in order to optimise its performances. Influence of the buffer gas on the PA signal has also been analysed, both theoretically and experimentally. A reduction of the PA signal of almost one order of magnitude has been observed between N(2) and He, which demonstrates the importance of the buffer gas in PA spectroscopy. Finally, detection limits of 0.5 ppm of CH(4) and 3 ppm of HCl has been achieved experimentally in nitrogen and an H(2)O sensitivity of 0.2 ppm has been estimated.     

Thermal resistance of composites based on nanodispersed aluminum

Thermolysis of low and high molecular aliphatic carboxylated compounds in composite systems based on nanosized aluminum were studied by the thermal desorption mass spectrometry. The conditions for maximal separation of the thermolysis products and their composition were determined. The kinetic parameters of thermal desorption and thermal degradation of the modifiers were calculated. Differences in the thermal stabilities of the polymer composites based on nanosized aluminum and different modifiers (carboxylated divinyl and divinyl nitrile oligomers) were presented.     

Low-Selective GaAs and GaSb Semiconductor Sensors for Potentiometric Analysis of Liquid Media

The possibility of using low-selective sensors based on gallium arsenide and gallium antimonide semiconductor compounds as indicators in acid-base, precipitating, and complexometric titration in model multicomponent systems and natural water was studied.     

Thermal optimization of a construction of a double-heterostructure GaAs/(AlGa)As diode laser

Analytical as well as computer aided thermal optimization of a construction of a stripegeometry double-heterostructure GaAs/(AlGa)As diode laser were performed in the present work. The influence of various construction parameters of the laser on its thermal resistance is shown.

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Zusammenfassung Die Konstruktion eines doppelt-heterostrukturellen GaAs/(AlGa)As Diodenlasers mit Streifengeometrie wurde sowohl analytisch als auch computergestützt thermisch optimiert. Es wurde der relative Einfluß verschiedener Konstruktionsparameter auf die Hitzebeständigkeit des Lasers gezeigt.

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This work was carried out under the Polish Central Program for Fundamental Research CPBP 01.06., 6.04.     

CE detector based on light-emitting diodes

CE detectors based on light-emitting diodes (LEDs) as light sources are receiving considerable attention due to their exceptionally high stability, high intensity, low cost, and a variety of wavelengths in the UV and visible spectrum. This article is a comprehensive review on CE methods using LED-based detectors with absorbance and fluorescence detection, and several applications on the determination of riboflavin, bacteria, drug, and amino acids in biological samples are described.     

Inductively Coupled Plasma Etching in ICl- and IBr-Based Chemistries. Part I: GaAs, GaSb, and AlGaAs

High-density plasma etching of GaAs, GaSb, and AlGaAs was performed inICl/Ar and IBr/Ar chemistries using an Inductively Coupled Plasma (ICP)source. GaSb and AlGaAs showed maxima in their etch rates for both plamachemistries as a function of interhalogen percentage, while GaAs showedincreased etch rates with plasma composition in both chemistries. Etchrates of all materials increased substantially with increasing rf chuckpower, but rapidly decreased with chamber pressure. Selectivities >10 forGaAs and GaSb over AlGaAs were obtained in both chemistries. The etchedsurfaces of GaAs showed smooth morphology, which were somewhat better withICl/Ar than with IBr/Ar discharge. Auger Electron Spectroscopy analysisrevealed equirate of removal of group III and V components or thecorresponding etch products, maintaining the stoichiometry of the etchedsurface.     

Thermal, rheological, and barrier properties of waterborne acrylic nanocomposite coatings based on boehmite or organo-modified montmorillonite

An organo-modified montmorillonite (Cloisite^®30B) or an unmodified boehmite (Disperal^®40) have been added to two acrylic latex dispersions (one of them UV-curable) for obtaining nanocomposite coatings. X-ray diffraction and transmission electron microscopy show a high degree of exfoliation in the nanocoatings based on montmorillonite, together with the deagglomeration of the micrometer-sized boehmite powder and the presence of single boehmite crystallites within the polymer matrix. Such morphologies are found to enhance the thermal and thermo-oxidative stability of the latexes and to significantly decrease their oxygen permeability, as well.     

A multi-wavelength photometer based on light-emitting diodes

The light originating from seven light-emitting diodes of different colours is guided, one at a time, into a measuring cell by means of a fibre optic coupler. Detection is carried out with photodiodes which are connected to a log-ratio amplifier yielding direct absorbance readings. Optical filters are used to narrow the emission band from blue light emitting diodes as these bands are relatively wide compared to those of the emitters of other colours. An inexpensive and compact multi-wavelength photometer covering the visible range is thus obtained, which in many cases can replace a conventional spectrophotometer for absorbance measurements. The performance for a range of commonly used photometric analytical procedures is described and compared to conventional measurements with a spectrophotometer.     

Heterolayer light-emitting diodes based on poly-phenylene vinylene

In order to enhance the quantum efficiency of poly-p-phenylene vinylene (PPV) light-emitting diodes (LEDs), we have fabricated metal/insulator/polymer (MIP) LEDs and heterolayer LEDs based on PPV and oxadiazole polymers. The current–voltage (I–V) characteristics and electroluminescence (EL) intensity of the MIP structures display a pronounced dependence of the insulator thickness and we detect an increase in the quantum efficiency of more than a factor of 30 at an AlO_x layer thickness of 3–6 nm. The device characteristics are qualitatively understood within inorganic metal insulator semi-conductor (MIS) theory and can be explained by a voltage-dependent barrier for minority carrier injection in connection with a hole-blocking barrier at the PPV/insulator interface. Our oxadiazole polymers used in the heterolayer polymeric devices are characterized by a high thermal stability and excellent film-forming properties. These materials act as efficient hole-blocking, electron transport and injection layers in PPV-based LEDs and we measure a significantly improved device performance with external quantum efficiencies of more than 0.5%. Temperature-dependent investigations point to a relatively balanced charge carrier injection and reveal the influence of space charge limited currents on the device performance at low temperature. © 1997 John Wiley & Sons, Ltd.     

Molecular diodes based on conjugated diblock co-oligomers

This report describes synthesis and characterization of a molecular diode based upon a diblock conjugated oligomer system. This system consists of two conjugated blocks with opposite electronic demand. The molecular structure exhibits a built-in electronic asymmetry, much like a semiconductor p-n junction. Electrical measurements by scanning tunneling spectroscopy (STS) clearly revealed a pronounced rectifying effect. Definitive proof for the molecular nature of the rectifying effect in this conjugated diblock molecule is provided by control experiments with a structurally similar reference compound.     

Thermal, optical and spectroscopic characterizations of borate laser crystals

The Yb-content Li₆Ln(BO₃)₃ (Ln: Gd, Y) solid solution has been investigated. Crystal growth has been successful for several compositions. A 22% molar content of ytterbium ions was determined by chemical analysis (ICP). Physical properties relevant to laser operation like mechanical hardness, thermal expansion and thermal conductivity were measured on single crystals. Optical measurements, including refractive index and low temperature spectroscopy, were also performed. Finally, the effect of the Y/Gd ratio is discussed.     

Sky-blue perovskite light-emitting diodes based on quasi-two-dimensional layered perovskites

A mixed organic(4-phenylbutylamine, 4-PBA) and inorganic(cesium, Cs) cations are used to deposit quasi-two-dimensional layered perovskites. This layered perovskites exhibit good film coverage as twodimensional perovskites and high emission performance close to three-dimensional organic–inorganic hybrid perovskites. Light-emitting diodes(LEDs) are fabricated by using solution process based on the quasi-two-dimensional layered perovskites. The perovskite LEDs exhibit a sky-blue emission with electroluminescence peak at 491 nm and a low turn on voltage at 2.9 V. The maximum external quantum efficiency reaches 0.015% at brightness of 186 cd/m~2.     

High power CW (16W) and pulse (145W) laser diodes based on quantum well heterostructures

We suggested and experimentally confirmed the effective method of internal optical loss reduction by high order mode suppression in a separate confinement quantum well laser heterostructure with asymmetric ultra thick waveguide. Manufacturing of InGaAs/GaAs/AlGaAs laser heterostructure with a 1.7 microm-thick asymmetric waveguide allowed attaining super low value of internal optical loss alphai=0.34 cm-1 preserving high efficiency and fundamental transverse mode operation. Record-high 16 W continuous wave (CW) and 145 W pulse room temperature front facet output optical power and 74% wallplug efficiency were attained in 100-microm-aperture 1.06-microm-emitting laser diodes with 3 mm cavity length.     

Measurement of the thermal impedance of laser diodes via thermal transients

The thermal impedance of laser diodes was determined by the measurement of thermal transients. The parameters of an equivalent R-C network were synthesized from the transient response. The network was compared with the real layer structure of the device. The effects of structure, mounting and aging on the temperature distribution were investigated with this method.

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Zusammenfassung Mittels Messung thermischer Einschwingvorgänge wurde die thermische Impedanz von Laserdioden bestimmt. Auf Grundlage des Sprungverhaltens wurden die Parameter eines äquivalentenR-C-Gliedes ermittelt, das mit der wahren Schichtenstruktur verglichen wurde. Mittels dieser Methode wurde der Einfluss von Struktur, Aufbau und Alterung auf die Temperaturverteilung untersucht.

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. R-C , . , .

     

Characteristics of vinyl iodide microwave plasma etching of GaAs/AlGaAs and InP/InGaAs heterostructures

Vinyl iodide (C₂H₃I) microwave discharges with additions of H₂ and Ar are found to provide faster etch rates than conventional CH₄/H₂/Ar discharges for InP, InGaAs, GaAs, and AlGaAs. This is a result of the relatively high volatilities of indium, gallium, and aluminum iodide species. The etched features are smooth and anisotropic over a wide range of do self-biases (–150 to –350 V), process pressures (1–20mTorr), and microwave powers (150–500 W). The polymer that forms on the mask during the plasma exposure can be readily removed in O₂ discharges. Electron spectroscopy for chemical analysis (ESCA) showed that the etched surfaces are slightly deficient in the group V elements under most conditions, but changes to the optical properties of the semiconductors are minimal. No defects are visible by transmission electron microscopy (TEM) in GaAs or InP samples etched at dc biases –250 V.