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Silver(I) ethylxanthate [AgS2COEt] (1) and antimony(III) ethylxanthate [Sb(S2COEt)3] (2) have been synthesised, characterised and used as precursors for the preparation of AgSbS2 powders and thin films using a solvent-free melt method and spin coating technique, respectively. The as-synthesized AgSbS2 powders were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The crystalline AgSbS2 powder was investigated using XRD, which shows that AgSbS2 has cuboargyrite as the dominant phase, which was also confirmed by Raman spectroscopy. SEM was also used to study the morphology of the resulting material which is potentially nanostructured. EDX spectra gives a clear indication of the presence of silver (Ag), antimony (Sb) and sulfur (S) in material, suggesting that decomposition is clean and produces high quality AgSbS2 crystalline powder, which is consistent with the XRD and Raman data. Electronic properties of AgSbS2 thin films deposited by spin coating show a p-type conductivity with measured carrier mobility of 81 cm2 V−1 s−1 and carrier concentration of 1.9 × 1015 cm−3. The findings of this study reveal a new bottom-up route to these compounds, which have potential application as absorber layers in solar cells.

The optical quality enhancement of a GaAs template grown on Silicon substrate using InGaAs/GaAs Dislocation Filters (DFs) combined with an annealing step have been assessed optically using Photoluminescence (PL) of embedded InAs/InGaAs QDs within a GaAs matrix. An annealing temperature after the growth of the DFs of 690 °C was shown to be optimum, giving an enhanced PL emission from the embedded InAs QDs in terms of intensity and Full Width at Half Maximum (FWHM). InAs quantum dots capped with GaAsSb grown at different temperatures were grown on the optimized GaAs template on Si. The prepared samples were characterized by PL, Atomic Force Microscopy (AFM), excitation power and dependent PL at 77 K and 300 K. At 77 K, the InAs/GaAsSb grown at 484 °C showed a type II band alignment with an emission wavelength of 1297 nm, which is shorter than the emission obtained from the reference sample, where the GaAsSb-capped dots were grown on GaAs (1357 nm). By reducing the GaAsSb capping layer growth temperatures to 465 °C and 450 °C, the wavelength at 77 K was extended to 1375 nm and 1480 nm respectively, resulting from an increased Sb content in the capping layer. At 300 K, a long wavelength emission of 1623 nm have been achieved.

In this work physical models of GaAs/AlAs and InGaAs/AlAs Asymmetric Spacer Layer Tunnel Diodes (ASPATs) with thin AlAs barriers were created using Silvaco ATLAS software. DC and RF characteristics of these ASPAT designs were obtained using the ATLAS semiconductor-insulator-semiconductor model. The simulated results were validated against measured results of fabricated ASPATs, grown using molecular beam epitaxy (MBE) with the same epitaxial designs. The models showed good scaling with device mesa area and good matching to both the DC and RF characteristics of the fabricated devices. Once experimentally validated models of the ASPAT diodes were produced, simulations were performed to investigate new metamorphic ASPAT devices in which InGaAs/AlAs devices are grown on GaAs substrates. These devices are the first demonstration of In 0.53 Ga 0.47 As/AlAs ASPATs grown on a GaAs platform. This has the potential to reduce cost and is a step forward for the manufacturability of low cost mmwave/THz detector devices. The simulations were compared with fabricated metamorphic ASPATs to better understand these new devices.

We have investigated the effect of antimony incorporation in GaAsSb as a capping layer on the optical properties of InAs quantum dots grown by Molecular Beam Epitaxy. Atomic Force Microscopy (AFM), High Resolution X-Ray Diffraction (HRXRD), photoluminescence (PL) and power dependent PL at 77 K and 300 K have been used for the characterization of the grown samples. Our analysis showed that the emission wavelength increases with Sb content and reaches ∼1.5 μm for Sb concentration of 22%. To achieve this wavelength, a reduction of the growth temperature of the GaAsSb layer from 500 °C to 440 °C was necessary. The wavelength increase is accompanied by a transition from a type I to type II band alignment and a broadening of the PL spectrum to a value of ∼237 nm for an excitation power of 100 mW. This broadening is attributed to the QD size inhomogeneity increase and Sb atoms redistribution during the in-situ annealing during the growth of the barriers at elevated temperature. Our results show the potential of the InAs/GaAsSb system in the development of broadband light sources and super-luminescent light emitting diodes in 1.2–1.5 μm wavelength range.

The electrical and optical properties of InGaN–GaN light-emitting diodes (LEDs) emitting in the 400–500-nm range and having a v-shaped quantum well (VSQW) and a u-shaped quantum well (USQW) are numerically investigated using APSYS simulation program. The simulation results showed that the devices containing VSQW have superior performance in terms of optical power and internal quantum efficiency droop compared to those with USQW. The optical power of the LEDs containing USQW increases gradually and reaches a maximum at 460 nm; however, the optical power of the LEDs with VSQW improves gradually, and the maximum is obtained in a window from 420 to 436 nm as a result of radiative recombination enhancement. The simulation results suggest that the higher performance of the VSQW is due to piezoelectric field reduction and an enhancement of electron and hole wave functions overlap.

In this work, we demonstrate the use of a digitally alloyed GaAsSb as a strain reducing layer (SRL) to tune the optical properties of InAs quantum dots grown on GaAs substrates. The GaAsSb digital alloy was made using a short period GaAs/GaSb superlattice. Increasing the Sb-shutter duty cycle (Sb-SDC) from 0 to 0.35 redshifts the emission wavelength from 1220 nm to 1492 nm at 300 K. The wavelength red shift is attributed mainly to the increased Sb content in the GaAsSb SRL as confirmed by high resolution X-ray diffraction. Power dependent photoluminescence showed a type II band alignment for the samples grown with a Sb-SDC of 0.25 and 0.35. Reversing the growth order of GaAs and GaSb layers and maintaining the same Sb-SDC (0.25) drastically alters the optical properties of the QDs. A large wavelength blue shift of 143 nm and a transformation from a type II to type I emission were observed as a result of GaSb intermixing with InAs QDs.

Due to their delta-like density of states, quantum dots (QDs) were expected to improve laser device performances with respect to quantum wells (QWs). Nevertheless, some important drawbacks limit this technology. For instance, QD laser still suffers from a low value of the modal gain, due to the low areal density of QDs, and inhomogeneous broadening, especially when multistacked layers are used. In this paper, we demonstrate that a linear increase of the QD modal gain with the QD layers number, as typically achieved in multi-QW lasers, is possible by a careful control of the Stranski-Krastanov QDs growth and QDs stacking optimization. A low-transparency current density of 10 A/cm(2) per QD layer and a modal gain of 6 cm(-1) per QD layer Were achieved from laser structures containing up to seven QD layers. We demonstrate 10-Gb/s direct modulation (until a temperature of 50 degrees C and high T-0 (110 K) from a single-mode device containing six QD layers.

In this work the analysis, fabrication and optical characterization of a circular two-dimensional photonic crystal (2D-CPC) nano-resonator based on a air/GaAs/air slab waveguide are presented. Four InAs/InGaAs quantum dots (QDs) stacked layers emitting around 1300 nm were embedded in a GaAs waveguide layer grown on an Al0.7Ga0.3As sacrificial layer. The nano-resonator was realized by drilling 2D-PC air holes arranged in a circular lattice configuration through electron beam lithography (EBL), inductively coupled plasma (ICP) etching and wet selective etching of the Al0.7Ga0.3As sacrificial layer in order to release the membrane. The spectral response of the active circular nano-cavity has been simulated by using a three dimensional finite-difference time-domain method (3D-FDTD) as a function of both the inner and outer holes radius/period ratios of the photonic crystal structure. Good agreement between the calculated resonance and the experimental results, recorded from the nano-cavity by a mu PL setup, has been achieved. (c) 2007 Elsevier B.V. All rights reserved.

International audience; Hydrostatic pressure and spontaneous emission techniques have been used to examine the important recombination mechanisms in type-I GaInAsSb/GaSb quantum well lasers. High pressure results indicate that Auger recombination dominates the threshold current of 2.11 μm and 2.37 μm devices and is the origin of their temperature sensitivity around room temperature. While the characteristics of the 2.37 μm devices are much improved by the suppression of the CHSH Auger process, since its spin-orbit splitting energy is greater than its band gap, other important Auger processes such as CHHL and CHCC persist. In the larger band gap 2.11 μm devices, an increase in threshold current with pressure is observed suggesting that CHSH Auger is present in these devices at atmospheric pressure and contributes to performance degradation at these shorter wavelengths.

Temperature-dependent optical gain, loss, and internal quantum efficiency have been measured for continuous-wave operated 2- μm InP laser from 10 °C to 70 °C using the Hakki-Paoli method. Modal gain and loss were extracted from the measured amplified spontaneous emission. The optical loss is constant with temperature, while the material gain decreases from 1128 cm-1 at 10 °C to 427 cm-1 at 70 °C. The internal efficiency decreases from 74% to 37% at 10 °C and 50 °C , respectively. The temperature sensitivity of threshold current is due to the decrease of the differential gain and a degradation of internal quantum efficiency.

In this letter, we report on experimental results of directly modulated single-transverse mode 1.3-mu m InAs-InGaAs quantum-dot (QD) lasers in a wide temperature range. A 3.125-Gb/s data modulation over temperature with an extinction ratio up to 10 dB is reported. Moreover, 10-Gb/s eye patterns at 15 degrees C and 50 degrees C and 5-Gb/s modulation in the whole explored temperature range (15 degrees C-85 degrees C) are demonstrated. These results were obtained by exploiting heterostructures containing six layers of high modal gain InAs QDs grown without incorporation of p-doping in the active region or tunnelling injection structure implementation. QD lasers exhibited a saturation modal gain as high as 36.3 cm(-1), ground state lasing from short cavities down to 400-mu m length and a characteristic temperature of about 110 K in a large temperature range between 15 degrees C and 85 degrees C.

Diode lasers emitting at 2.26 /spl mu/m, based on the InGaAsSb-AlGaAsSb materials system, are reported. These devices exhibit high internal quantum efficiency of 78% and low threshold current density of 184.5 A/cm/sup 2/ for a 2-mm-long cavity. Output power up to 700 mW (/spl ap/550 mW) has been obtained at 280 K (300 K) in continuous-wave operation with 100 /spl mu/m/spl times/1 mm lasers. These devices have been coated with an antireflection on the output facet and are mounted epilayer down on a copper block. The working temperature was maintained by a thermoelectric Peltier cooling element.

In this paper, c-plane stepped- and graded- InGaN/GaN multiple quantum wells (MQWs) are grown using plasma assisted molecular beam epitaxy (PAMBE) by in situ surface stoichiometry monitoring (i-SSM). Such a technique considerably reduces the strain build-up due to indium clustering within and across graded-MQWs; especially for QW closer to the top which results in mitigation of the quantum-confined Stark effect (QCSE). This is validated by a reduced power dependent photoluminescence blueshift of 10 meV in graded-MQWs as compared to a blueshift of 17 meV for stepped-MQWs. We further analyze microstrain within the MQWs, using Raman spectroscopy and geometrical phase analysis (GPA) on high-angle annular dark-field (HAADF)-scanning transmission electron microscope (STEM) images of stepped- and graded-MQWs, highlighting the reduction of ~1% strain in graded-MQWs over stepped-MQWs. Our analysis provides direct evidence of the advantage of graded-MQWs for the commercially viable c-plane light-emitting and laser diodes.

We report the dry etch of GaSb(001) by inductively coupled plasma reactive ion etcher. Silicon Oxide, deposited by PECVD, was used as a mask. The oxide layer proved to be almost unaffected compared to the GaSb, when using chlorine compound gases as etchants (Cl2, BCl3, and SiCl4) as well as argon. This provides high selectivity for GaSb to the mask layer. The sample holder has no silicon that may contribute to the etching process. Etching using Cl2 + Ar showed increase in the etching rate as the chlorine ratio increases; however, the process led to grassy surface and chemical like reaction. The use of SiCl4+Cl2+Ar mixture with low chlorine ratio resulted in anisotropic etch with smooth sides. It has been found for this case that the increase of the chlorine ratio led to an increased etching rate as well. The repeat of previously reported result by Swaminathan et al. [Thin Solid Films 516 (2008) 8712.] yet with a sample holder not having silicon, proved the effect of Si-contribution in producing vertical profile etch with smooth surfaces.

We report the results of an extensive optical investigation by continuous-wave and time resolved photoluminescence experiments on double GaInAsSb∕AlGaAsSb quantum wells emitting at 2.3μm at room temperature. We have found that, at low temperature (

High saturation modal gain InAs/InGaAs quantum dot (QD) lasers operating at 1.3 micron have been successfully demonstrated, thus enabling high frequency operation, high temperature stability and ultra-small cavity lasers.

In this contribution we show the fabrication of functional hybrid organic-semiconductor microtubes obtained by combining the self-rolling of In0.2Ga0.8As/GaAs layers with the deposition of polymer multilayers obtained by Layer-by-Layer (LbL) self-assembly. It was demonstrated that the polymer multilayers are compatible with the selective etching exploited for the channel formation and that reactivity to an external stimulus (e.g. pH) is maintained after the hybrid structure formation. (C) 2008 Elsevier B.V. All rights reserved.

In this work, we show that a modal gain as high as 42cm-1 could be achieved from a device containing 7 InAs/InGaAs stacked QD layers. The enhancement of the modal gain is accompanied by a decrease of the threshold and transparency current densities per QD layer down to 16 and 7 A cm-2, respectively. Moreover, a linear increase of the modal gain with the number of QD layers is observed. The obtained high modal gain allows us to achieve good temperature stability and high-speed operation in a wide temperature range. Modulation eye diagrams under 10 Gb/s are achieved in 15degC-50degC range in a single- transverse mode 1.3mum QD lasers. High characteristic temperature of about 110 K between 15degC and 85degC are reported.

We report on the fabrication and characterization of single-transverse mode 1.3 μm InAs/InGaAs QD lasers in a wide temperature range. Open eye patterns up to 10 Gb/s are reported, whereas a characteristic temperature of about 110 K has been measured in the whole temperature range (15°C - 85°C). These results were obtained by exploiting heterostructures containing six-layers of high modal gain InAs quantum dots grown without incorporation of p-doping. QD lasers exhibited a saturation modal gain as high as 6 cm-1 per QD layer, which linearly increases with the numbers of the quantum dot layers.

We propose the simulation and the fabrication of a photonic crystal (PhC) strain-sensitive structure, showing that the optical properties of photonic crystals can be used to realize sensing devices characterized by a high degree of compactness and good resolution. The force/pressure optical sensor has been realized by designing a bulk GaAs/AlGaAs photonic crystal microcavity operating in the wavelength range 1300-1400 nm. The simulations show that the resonant wavelength of the mode localized in the microcavity shifts its spectral position following a linear behaviour when a pressure ranging between 0.25 Gpa and 5 GPa is applied, thus allowing the possibility to achieve pressure resolution of 5.82 nm/GPa. High-resolution electron beam lithography technique followed by inductively coupled plasma process were used to transfer the designed geometry on the sample. (c) 2007 Elsevier B.V. All rights reserved.

A new and compact photoacoustic sensor for trace gas detection in the 2-2.5 μm atmospheric window is reported. Both the development of antimonide-based DFB lasers with singlemode emission in this spectral range and a novel design of photoacoustic cell adapted to the characteristics of these lasers are discussed. The laser fabrication was made in two steps. The structure was firstly grown by molecular beam epitaxy then a metallic DFB grating was processed. The photoacoustic cell is based on a Helmholtz resonator that was designed in order to fully benefit from the highly divergent emission of the antimonide laser. An optimized modulation scheme based on wavelength modulation of the laser source combined with second harmonic detection has been implemented for efficient suppression of wall noise. Using a 2211 nm laser, sub-ppm detection limit has been demonstrated for ammonia. © 2005 Elsevier B.V. All right reserved.

The temperature dependence of the threshold current of InGaAsSb/AlGaAsSb compressively strained lasers is investigated by analyzing the spontaneous emission from working laser devices through a window formed in the substrate metallization and by applying high pressures. It is found that nonradiative recombination accounts for 80% of the threshold current at room temperature and is responsible for the high temperature sensitivity. The authors suggest that Auger recombination involving hot holes is suppressed in these devices because the spin-orbit splitting energy is larger than the band gap, but other Auger processes persist and are responsible for the low T0 values.

A semiconductor laser containing seven InAs-In-GaAs stacked quantum-dot (QD) layers was grown by molecular beam epitaxy. Shallow mesa ridge-waveguide lasers with stripe width of 120 mu m were fabricated and tested. A high modal gain of 41 cm(-1) was obtained at room temperature corresponding to a modal gain of similar to 6 cm(-1) per QD layer, which is very promising to enable the realization of 1.3-mu m ultrashort cavity devices such as vertical-cavity surface-emitting lasers. Ground state laser action was achieved for a 360-mu m-cavity length with as-cleaved facets. The transparency current density per QD layer and internal quantum efficiency were 13 A/cm(2) and 67%, respectively.

First investigations of photoacoustic (PA) spectroscopy (PAS) of methane using an antimonide semiconductor laser are reported. The laser fabrication is made in two steps. The structure is firstly grown by molecular beam epitaxy, then a metallic distributed-feedback (DFB) grating is processed. The laser operates at 2371.6 nm in continuous wave and at room temperature. It demonstrates single-mode emission with typical tuning coefficients of 0.04 nm mA-1 and 0.2 nmK-1. PA detection of methane was performed by coupling this laser into a radial PA cell. A detection limit of 20 ppm has been achieved in a preliminary configuration that was not optimised for the laser characteristics. © 2004 Elsevier B.V. All rights reserved.

International audience; We report on low-threshold high-power quantum well diode lasers emitting near 2.3 μm based on the GaInAsSb/AlGaAsSb system. The threshold current density per quantum well is as low as 63 A cm-2. A maximum output power of 540 mW at 293K in the continuous wave regime has been achieved.

International audience; We have grown semiconductor lasers by molecular beam epitaxy (MBE) on [100] oriented GaSb:Te substrates. An 80% internal quantum efficiency was deduced from measurements of the external quantum efficiency versus cavity length. Internal losses as low as 7 cm/sup -1/ have been found. The system is able to reach threshold current densities as low as 63 A/cm/sup 2/ per well for a cavity length of 1200 /spl mu/m. This is, to our knowledge, the best reported value at 2.26 /spl mu/m.

In-plane absorption measurements were performed at room temperature by means of a waveguide transmission setup on a Stranski-Krastanov InAs dots-in-a-well system emitting at 1.3 mu m embedded in a p-i-n structure. The polarization dependence of quantum dot (QD) absorption was exploited to resolve its discrete and continuous spectral components and study them separately under reverse bias application. The quantum confined Stark effect observed in the discrete spectral component gave evidence of an upward built-in QD dipole of about 9.5x10(-29) C m. The continuous component was found to originate from electronic transitions involving a QD state and a quantum well state. (C) 2008 American Institute of Physics. (DOI: 10.1063/1.3000381)

Double quantum well laser diodes based on the GaInAsSb/AlGaAsSb system emitting at 2.61 /spl mu/m in continuous-wave regime have been fabricated. In the pulsed regime for a 100 /spl mu/m-wide 1600 /spl mu/m-long device a record threshold current density of 76 A/cm/sup 2/ per quantum well was obtained.

We report on the growth, fabrication and characterization of low threshold laser diodes emitting around 1.3 gim. The quantum dot active region was optimised to get the highest photoluminescence emission and the lowest Full Width at Half Maximum (FWHM). Broad area laser diodes were processed from different samples containing three layers of InAs quantum dots (QDs), and cleaved at different cavity lengths (L c ). Electro-luminescence measurements were performed at room temperature under pulsed excitation. The laser diodes operate at room temperature and emit at 1.32 μm, in the low-absorption spectral window for telecom applications. The characteristic temperature T 0 is in the range 60-77 K and the differential quantum efficiency is 53 %. For an infinite cavity length a threshold current density of 8 A/cm2per QD layer was obtained. Lasing from short-cavity diodes (L c = 750 μm) was also obtained after e-beam evaporation of high-reflection coatings on one edge of the in-plane laser structure.