Juan Martínez-Pastor

Complete ground state gain recovery after ultrashort double pulses in quantum dot based semiconductor optical amplifier

Gain recovery dynamics are studied in electrically pumped quantum dot (QD) based semiconductor optical amplifiers (SOAs) after amplification of double femtosecond laser pulses using ultrafast pump-probe spectroscopy with heterodyne detection. The authors observe a distinct change in gain recovery in the ground state when a significant excited state population is achieved. A complete gain recovery is found when two 150fs pulses with 5ps time delay pass through the SOA in resonance to the ground state under high injection currents of 80–100mA. The obtained results open the way for ultrafast (>200GHz) operation in p-doped QD based SOAs at 1.3μm telecommunications wavelengths.

Electrical and photovoltaic properties of indium‐tin‐oxide/p‐InSe/Au solar cells

Conditions for efficiency improvement and optimization in indium‐tin‐oxide/p‐indium‐selenide solar cells are discussed in this paper. This aim is achieved by using low‐resistivity p‐indium‐selenide and by incorporating a back‐surface‐field contact. This contact is insured by a p‐indium selenide/gold barrier whose rectifying behavior is explained through the complex impurity structure of p‐indium‐selenide. Electrical and photovoltaic properties of the cells are also reported. The efficiency parameters under AM1 simulated conditions have been improved up to 32 mA/cm2 for the short‐circuit current density, 0.58 V for the open‐circuit voltage, and 0.63 for the filling factor. As a result, solar efficiencies larger than 10% in annealed cells and 8% in unannealed ones have been attained. The limitations of these devices are discussed by investigating the dependence of electrical and efficiency parameters in function of photon flux and temperature.

Electronic structure, optical properties, and lattice dynamics in atomically thin indium selenide flakes

The progressive stacking of chalcogenide single layers gives rise to two-dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide (InSe) is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness (as large as 0.2 eV for three single layers). First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies.

High-resolution electron-beam patternable nanocomposite containing metal nanoparticles for plasmonics

Polymer nanocomposites containing noble metal nanoparticles are promising materials for plasmonic applications. In this paper, we report on a high-resolution negative-tone nanocomposite resist based on poly(vinyl alcohol) where silver nanoparticles and nanopatterns are simultaneously generated by electron-beam lithography. Our results indicate nanostructures with a relatively high concentration of nanoparticles and, consequently, an electromagnetic coupling among the nanoparticles. Therefore, the patternable nanocomposite described in this work may be a suitable material for future plasmonic circuitry.

Optical transitions and excitonic recombination in InAs/InP self-assembled quantum wires

InAs self-assembled quantum wire structures have been grown on InP substrates and studied by means of photoluminescence and polarized-light absorption measurements. According to our calculations, the observed optical transitions in each sample are consistent with wires of different heights, namely from 6 to 13 monolayers. The nonradiative mechanism limiting the emission intensity at room temperature is related to thermal escape of carriers out of the wires.

Nanotexturing To Enhance Photoluminescent Response of Atomically Thin Indium Selenide with Highly Tunable Band Gap.

Manipulating properties of matter at the nanoscale is the essence of nanotechnology, which has enabled the realization of quantum dots, nanotubes, metamaterials, and two-dimensional materials with tailored electronic and optical properties. Two-dimensional semiconductors have revealed promising perspectives in nanotechnology. However, the tunability of their physical properties is challenging for semiconductors studied until now. Here we show the ability of morphological manipulation strategies, such as nanotexturing or, at the limit, important surface roughness, to enhance light absorption and the luminescent response of atomically thin indium selenide nanosheets. Besides, quantum-size confinement effects make this two-dimensional semiconductor to exhibit one of the largest band gap tunability ranges observed in a two-dimensional semiconductor: from infrared, in bulk material, to visible wavelengths, at the single layer. These results are relevant for the design of new optoelectronic devices, including heterostructures of two-dimensional materials with optimized band gap functionalities and in-plane heterojunctions with minimal junction defect density.

Localized surface plasmon resonance sensor based on Ag-PVA nanocomposite thin films

In this work we demonstrate the use of nanocomposite thin films of poly(vinyl alcohol) with embedded silver NPs for chemosensing purposes. Silver NPs are in situ synthesized inside polyvinyl alcohol during the bake step of the formation of a nanocomposite thin film. The polymer in the nanocomposite provides an appropriate chemical and electromagnetic environment for metal NPs in order to interact with and hence detect the chemical species. A limit of detection below 20 nM is found when detecting 2-mercaptoethanol as the analyte, when measuring spectral changes (peak wavelength, linewidth and intensity) in the Localized Surface Plasmon Resonance. Potential qualitative and semi-quantitative sensors based on such nanocomposites would be easy-to-prepare, easy-to-use and low-cost, which are the basis of a fully disposable sensing platform technology.

Polymer/Perovskite Amplifying Waveguides for Active Hybrid Silicon Photonics

The emission properties of hybrid halide perovskites are exploited to implement a stable and very low power operation waveguide optical amplifier integrated in a silicon platform. By optimizing its design with a poly(methyl methacrylate) (PMMA) encapsulation, this novel photonic device presents a net gain of around 10 dB cm(-1) and 3-4 nm linewidth with an energy threshold as low as 2 nJ pulse(-1) and exhibiting no degradation after one year.

Plasmonic communications : light on a wire

By coupling light to the charges at metal interfaces, plasmonics enables scientists to manipulate photons in a way they never have before: at the subwavelength level. With its potential to produce ultra-compact devices that relay information almost instantaneously, plasmonics may be the next big-and small-thing in optical communications.

Morphological Characterisation of Bacterial Cellulose-Starch Nanocomposites

Acetobacter sp. growing medium was modified in order to produce bacterial cellulose (BC) nanocomposites using a bottom-up technique that allowed starch to be introduced into the cellulose network. The BC-starch mats were hot-pressed to obtain nanocomposites sheets. Morphological characterisation was carried out using Atomic Force Microscopy and Environmental Scanning Electron Microscopy. The images obtained from microscopy were then processed using image analysis. Network properties, such as mesh size and fibre orientation were characterised. Fracture surfaces of these new nanocomposites were analysed.