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The knowledge of viscosity, which determines the flow of material under applied stresses, is important for many processes of the material production. Data on viscosity of thin amorphous films are necessary for development of molding technology, which allows fast fabrication of various components for integrated optics. Chalcogenide films attract great attention due to their non-linear optical properties and possibility of viscosity variation by light illumination. Despite of importance of data on the film viscosity, no methods of their direct measurements were reported. We propose such method and apply it for measurements of viscosity of As20Se80 chalcogenide films in a temperature range 378–403 K. We have obtained that coefficients of viscosity vary in the range 3 × 107–1010 Pa·s, with the activation energy 2.9 eV. The thin film viscosity coefficients are 2–5 times smaller compared to those for massive glasses.

We have systematically studied the optical properties, the effect of laser illumination, and the effect of light induced surface deformation through direct fabrication of surface relief gratings (SRGs) on As30Se70 thin films. The transmittance, T, for as deposited and illuminated films show a red shift in the transmittance edge which associated with the decrease in energy gap and this confirms the photo-darkening effect. The variations in linear and non-linear optical parameters values have been discussed in the view of illumination effect. Giant stable surface relief gratings have been obtained by one-step holographic recording. The surface relief gratings formation in our film is investigated by atomic force microscopy (AFM). Results have been analysed in terms of available theories for these phenomena.

(Ag 3 AsS 3 ) 0.9 (As 2 S 3 ) 0.1 thin films with high concentration of silver were deposited by a rapid thermal evaporation, their structural properties were studied using SEM and AFM. Roughness analysis of as-deposited films surfaces was performed. The influence of laser and e-beam irradiation on structural and optical properties was analysed. It is shown that e-beam, as well as laser illumination, causes a formation of flakes, bubbles on the surface of the films. Holographic gratings were recorded on the given films using green laser. Optical transmission kinetics with laser illumination shows its increase with illumination time.

Direct surface relief recording in amorphous chalcogenide semiconductors like As20Se80 and other compositions from As(Ge)–S(Se) systems essentially depends on the chemical composition, technology, and the recording conditions, resulting discrepancies in the results and interpretations. We have developed a method of direct comparison of the relief height and form in a combined thin film samples made of the reference and investigated compositions, as well as simple way of determining the efficiency of mass transport at surface relief recording. Selection of the a-Se as reference layer enables consideration of the possible role of composition, temperature, polarization in the recording process for any other chalcogenide or other material, which possess similar relief recording effects.

Surface reliefs in the form of dots and surrounding rings were recorded by focused laser beam on bulk amorphous selenium samples with an aim to separate the possible contributions of pure light- and thermally stimulated effects to the relief formation process. It is concluded, that heating by the light beam can be cross-linked with light induced mass transport in the gradient of illumination and temperature fields and so with surface relief formation, influencing its efficiency and quality. Such thermal effects should be taken into account in light sensitive chalcogenide glasses with low softening temperatures and possible crystallization effects.

Two InGaP/AlGaInP red laser diodes are studied at pressures up to 16 kbar and at temperatures down to 80 K. Emission wavelengths below 570 nm have been obtained, with low thresholds and high efficiencies. Pressure dependence of threshold currents is very different for the two lasers indicating that electron leakage occurs predominantly to L minima in one laser and to X minima in another laser.

Red laser diodes emitting at 636 nm and 645 nm are studied as a function of pressure up to 20 kbar and temperature from 300 K down to 80 K. The 636 nm samples reveal anomalous L-I- V dependence at low temperatures and at high pressures. The 645 nm samples do not show these anomalies and can be tuned by pressure and temperature down to 575 nm, i.e., in the 70 nm range with powers above 200 mW and low threshold currents.

In the present paper we demonstrate that wide-range wavelength tun-ing of semiconductor lasers can be achieved by applying high pressure andlow temperature. We report the experimentally measured dependence ofthe threshold current and emission energy on pressure and temperature inInGaAs/GaAs quantum-well lasers and provide the simple theoretical expla-nation of the physics behind the experimental flndings.PACS numbers: 42.55.Px, 85.60.Jb

Tapered lasers offer high beam quality together with high power. Wavelength tunability is therefore a valuable feature for such laser, making it a compact alternative for e.g. Titanium-Sapphire laser. We demonstrate the combination of fine tuning by grating (in the 30 nm range) with the coarse tuning by pressure (up to 12 kbar) for a high power tapered laser emitting around 960 nm at ambient pressure. At the fixed current of 1.5 A the laser was tuned in a 100 nm range (from 980 nm to 880 nm) emitting between 200 mW and 300 mW with high quality of the beam. We examined the possibility of using pressure-tuned tapered laser diodes in spectroscopy and we demonstrated high spatial resolution for photocurrent and photoreflectance measurements.

We demonstrated the pressure and external cavity tuning of commercial telecommunication laser, emitting in the 1500 nm band under normal conditions. The laser had AR coatings on the output mirror and highly reflective coating on its back facet. We measured the tuning ranges of the laser operating CW under four different pressures. The experimental setup was in the Littrow configuration. At each pressure the external cavity arrangement enabled the fine tuning in the range of the positive modal gain. We determined the net gain from the Hakki-Paoli method. The combination of pressure tuning with grating allowed us to obtain the 350 nm tuning range (from 1575 nm to 1225 nm).

Pressure and temperature change the bandgap of III-V semiconductors and therefore they shift the gain spectrum of laser diodes. With 20 kbar pressure (achievable in a liquid pressure cell) we can increase the energy of the laser emission by about 200 meV for lasers grown on GaAs, InP, or GaSb. The main physical limitation of pressure tuning for shorter wavelengths (i.e. between 600 and 800 nm) is the reduction of indirect gap (Γ-X) in the barriers and claddings of the laser structure, leading to strong increase of leakage and threshold currents. In this wavelength range temperature tuning seems more practical. Cooling down the laser from room temperature (300 K) to about 100 K we should be able to increase the emission energy by about 80 meV. The combination of pressure/temperature tuning with tuning by external grating turned out to combine the merits of both methods: wide spectral range, narrow linewidth, stable emission wavelength. The method seems promising although several issues still have to be addressed like the reliability of lasers and pressure cells after multiple pressure cycles, stability of coupling between the laser diode and fiber under high pressure etc.

We show that the hydrostatic pressure coefficient dE E /dp of luminescence in In x Ga 1-x N epilayers is in the range 20-38 meV/GPa for the entire alloy (0 > x > 1) and corresponds roughly to the bandgap increase with applied pressure. It is argued that lowering of dE E /dp in quantum structures of InGaN with respect to this range can be attributed to polarization-induced electric fields (PIEFs). Possible contribution to dE E /dp originating from In-segregation effects is of secondary importance. This information is used to investigate PIEF screening by free carriers in InGaN-based light emitting diodes (LEDs). We observe that Si doping at a level of 10 19 cm -2 of the barriers in the active region of such LEDs leads to a significant increase of dE E /dp as compared to LEDs with undoped barriers. This is evidence for efficient screening of PIEFs in the Si-doped devices.

Homogeneous, 200 – 3000 nm thick layers of chalcogenide glasses, 1 – 2 mm thick plane-parallel plates as well as nanocomposite structures, containing gold nanoparticles have been produced and used for in situ surface optical and geometrical relief fabrication by optical- or electron-, ion-beam recording. Investigations were focused on the formation of giant (height modulation from nanometers up to micrometers) geometrical reliefs and elements (dots, lines and diffractive elements) applicable in the 0.5 – 10 micrometer spectral range. Recording parameters were compared with available data on acrylic polymer nanocomposites. The mechanism of the recording processes, which include thermal, electron and mass-transport components were explained and the selection of the materials from As(Ge)-S(Se) binary systems with best recording parameters was done.

By means of hydrostatic pressure-dependent measurements of the electroluminescence of blue/violet laser diodes with In0.1Ga0.9N/GaN active layers grown on bulk GaN it is shown that at conditions close to lasing threshold full screening of polarization-induced electric fields (PIEFs) is provided by injected charge. In contrast, in order to achieve PIEF screening at currents much below lasing threshold, Si doping of quantum barriers is seen to be necessary. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate screening of polarization induced electric fields in a group III-nitride based laser diode with InGaN active layers. Via hydrostatic pressure dependent electroluminescence measurements and additional photocurrent spectroscopy experiments, it is shown that the introduction of Si doping with a concentration of 1.10 1 9 cm - 3 in the barriers of the active region leads to adequate screening of polarization induced electric fields.

Anomalous behavior is investigated of differential resistance dU/dI of laser diodes at the lasing threshold. The regular case is the known decrease of the dU/dI associated with a dynamic saturation of the junction voltage. In contrast to this, the anomalous case is an increase of the differential resistance (the "positive kink" of dU/dI). Some regular samples are found to show the anomaly at lower temperature or at high hydrostatic pressure. The anomaly is discussed in terms of the injection-induced conductivity.

InGaP/AlGaInP lasers (emitting from 630 to 690 nm) and GaAs/ AlGaAs lasers (emitting at 780 nm) were studied under hydrostatic pressure up to 20 kbar and at temperatures from 240 to 300 K. The electrical characteristics, the power-current dependencies and the emission spectra were measured. The emission spectra shifted in agreement with the pressure/temperature variation of the band gaps in active layers of the laser. Since at high pressure the Γ-X separation in the conduction band is strongly reduced (both in AlGaInP and AlGaAs), the dominant loss mechanism of the lasers is the electron leakage to X minima in the p-claddings. This, in turn, leads to high sensitivity of threshold currents to temperature. The dependence of threshold currents on pressure and on temperature is in good agreement with the simple theoretical analysis taking into account the carrier leakage and the radiative and nonradiative recombination. Better agreement between the theory and the experiment is obtained assuming drift rather than diffusion leakage. This indicates that threshold currents could be further reduced if the p-doping is improved in the claddings.

(Ag3AsS3)0.6(As2S3)0.4 thin films were deposited upon a quartz substrate by rapid thermal evaporation. Structural studies of the as-deposited, annealed and illuminated films were performed using XRD, scanning electron and atomic force microscopies. Surfaces of all the films were found to be covered with Ag-rich crystalline micrometer sized cones. Thermal annealing leads to mechanical deformation of part of the cones and their detachment from the base film surface while the laser illumination leads to the new formations appearance on the surface of thin films. The spectroscopic studies of optical transmission spectra for as-deposited, annealed and illuminated thin films were carried out. The optical absorption spectra in the region of its exponential behaviour were analysed, the dispersion dependences of refractive index as well as their variation after annealing and illumination were investigated.

A fiber feedthrough for a semiconductor laser located in a high (20–22 kbar) hydrostatic pressure cell is a convenient tool for making electrooptical measurements of materials at high hydrostatic pressures. A prototype of a semiconductor laser tuned by high hydrostatic pressure has been developed. A simple method for supplying electric power to samples inside the pressure cell is described.

We demonstrate efficient wavelength tuning by means of hydrostatic pressure of an InGaN/GaN laser diode grown on bulk GaN crystal. Energy shifts of the emitted light with pressure have been found to be about 36 meV/GPa, which are high magnitudes for nitride-based device structures. This result is interpreted as being indicative of efficient screening of built-in electric fields in the studied device. Furthermore, the threshold current of the laser diode was found to be independent of applied pressure. The high magnitude of the pressure coefficient allowed for the achievement of a laser tuning range of up to 10 nm in the blue/violet region, using compact pressure equipment.

High hydrostatic pressure can be used for wavelength tuning of semiconductor laser diodes in a wide spectral range. Coupling the laser with external grating leads to wavelength tuning within the gain spectrum (i.e. in a narrower range than with pressure) but allows for a narrow emission line and nearly continuous tuning (mode-hop free if anti-reflecting coating is applied). Here we demonstrate a combination of pressure and external-resonator tuning for the GaInNAs laser emitting at 1343 nm at ambient conditions. Using the specially designed liquid pressure cell working up to 20 kbar we shift the emission down to 1170 nm while the external grating (used in Littrow configuration) allows for fine tuning in the ~10 nm range (at each pressure).

InGaAsSb∕AlGaAsSb type-I midinfrared diode lasers emitting continuous wave at 2.4μm at room temperature have been studied under high hydrostatic pressure. When the pressure was increased up to 19kbar, the threshold current varied from 240to400A∕cm2, showing a minimum of 200A∕cm2 close to 8kbar, and the emission spectra shifted to shorter wavelengths by up to 700nm (i.e., from 2.4μmto1.7μm). This exceptional tuning range could be very useful in tunable diode laser absorption spectroscopy.

Wide-range wavelength tunability is demonstrated for commercial high-power laser diodes emitting at 980 nm, 830 nm, and at 808 nm. High pressure shifts the emission wavelength of the lasers due to the increase of bandgaps in the active layers with the rate of about 10 meV per kbar. For the 980 nm InGaAs/GaAs laser the threshold currents and the differential efficiencies remain constant with pressure which allows for the constant operating current and the emitted power in the full tuning range. For 830 nm and 808 nm GaAs/AlGaAs lasers there is an increase of threshold currents with pressure related to the leakage through X minima in the conduction band of AlGaAs. This limits the tuning range unless we operate the laser at lower temperature. We designed the pressure cell with Peltier cooling allowing for independent control of temperature down to 0 Celsius and pressure up to 20 kbar. The laser beam passes through the sapphire window or through the multi-mode fiber. Our device allows for the tuning of 980 nm laser down to 840 nm, 830 nm laser down to 745 nm, and 808 nm laser down to 720 nm. We were able to keep the output power fixed in the full tuning range: 300 mW for the 980 nm laser and 400 mW for the 830 nm and 808 nm lasers.

Two InGaP/AlGaInP lasers (emitting at 660 nm and at 690 nm) and one GaAs/AlGaAs laser (emitting at 780 nm) have been studied under hydrostatic pressure up to 20 kbar and at temperatures from 240 K to 300 K. The power-current characteristics and the spectra have been measured in the specially designed pressure cell. The emission spectra shifted in agreement with the pressure/temperature variation of the bandgaps in active layers of the lasers. Since at high pressure the Γ-X separation in the conduction band is strongly reduced (both in AlGaInP and in AlGaAs) the dominant loss mechanism of the lasers is the carrier leakage to X minima in the claddings. This, in turn, leads to high sensitivity of threshold currents to temperature. The dependence of threshold currents on pressure and on temperature is in good agreement with the simple phenomenological analysis taking into account the carrier leakage and the radiative and nonradiative recombination. Good description of the pressure and temperature variation of the threshold currents is obtained using three adjustable parameters. Our fits indicate that the dominant contribution to electronic leakage is drift rather than diffusion. These results are important for the application of pressure/temperature tuning of laser diodes in the 600-800 nm range. In particular, we were able to turn red laser diodes into yellow (emitting below 600 nm) and infrared 780 nm lasers into bright red. By simultanous control of pressure and temperature it is possible to obtain constant emission power of the lasers in the full tuning range (at a fixed operating current).

Direct bandgap of most III-V semiconductors (AlGaAs, InGaAs, InGaP, InAs) increases with hydrostatic pressure at the rate of about 10 meV per kbar. Thus the emission wavelength of semiconductor lasers shifts to the blue under the application of high pressure. We demonstrate that this effect can be used for wavelength tuning of laser diodes in a very wide spectral range. Using the specially designed liquid pressure cell working up to 20 kbar the 1550 nm laser was tuned down to 1270 nm, the 1300 nm laser was tuned down to 1100 nm, and the 980 nm laser was tuned down to 840 nm. The emitted light passes through the sapphire window or through the fiber directly coupled to the laser. The threshold current and the quantum efficiency for the 980 nm laser remained constant with pressure, for the two other lasers the thresholds decreased with pressure. Thus we obtained the constant emission power in the full tuning range. We hope that this compact device will find applications as a tool for characterization of some optical network devices or parts of optical transmission lines.

We demonstrate wide-range tuning of an 830 nm InGaAsP laser diode by pressure and temperature combined with tuning by external grating. Pressure tuning (up to 11 kbar) yields the wavelength range of 70 nm limited by the increase of the threshold current. Temperature tuning from room temperature down to 90 K yields the wavelength range of 56 nm. The reliability of the lasers subjected to pressure or temperature cycles seems to be mainly related to mounting-induced strains, i.e. the choice of proper submount is crucial. The tuning range achieved with external grating decreases at high pressure (and at low temperature).

The emission wavelength of broad-area AlGaInP/InGaP quantum-well lasers is tuned by the application of high hydrostatic pressure and low temperature from 645 down to 575 nm, i.e., from the red through the orange to yellow spectral range. Emission powers up to 300 mW are obtained in the full tuning range. The pressure and temperature dependence of threshold currents indicates that leakage occurs into the L and X minima in the barriers.

Photocurrent spectroscopy and hydrostatic-pressure-dependent electroluminescence are used to show that heavy 1×1019cm−3 Si doping of quantum barriers is sufficient to achieve full screening of polarization-induced electric fields (PIEFs) in nitride light emitting diodes (LEDs) and laser diodes (LDs) with InGaN quantum wells. Furthermore, it is shown that at currents close to lasing threshold in nitride LDs injected charge alone is sufficient to achieve full screening of PIEFs. In contrast, full screening at low currents can only be accomplished via Si doping of quantum barriers.