Bassem Salem

Bio: Bassem Salem is an academic researcher from University of Grenoble. The author has contributed to research in topics: Nanowire & Quantum dot. The author has an hindex of 21, co-authored 137 publications receiving 1504 citations. Previous affiliations of Bassem Salem include Université de Sherbrooke & Université de Montréal.

Surface effects on shape, self-organization and photoluminescence of InAs islands grown on InAlAs/InP(001)

Abstract: InAs nanostructures were grown on In0.52Al0.48As alloy lattice matched on InP(001) substrates by molecular beam epitaxy using specific growth parameters in order to improve island self-organization. We show how the change in InAs surface reconstruction via growth temperature from (2×4) to (2×1) and/or the use of InAlAs initial buffer surface treatments improve the island shape homogeneity (either as quantum wires or as quantum dots). Differences in island shape and in carrier confinement are shown by atomic force microscopy and by photoluminescence measurements, respectively. We point out that such shape amendments induce drastic improvements to island size distribution and discernible changes in photoluminescence properties, in particular concerning polarization.

From large to low height dispersion for self-organized InAs quantum sticks emitting at 1.55 μm on InP (001)

Abstract: We show how the height dispersion of self-organized InAs/InP(001) quantum islands emitting at 1.55 μm was reduced by optimizing the epitaxial growth parameters. Low height dispersion was obtained when the InAs deposit thickness was much greater than the critical thickness for two-dimensional/three-dimensional growth mode transition, and when adatom surface diffusion was favored by increasing the growth temperature or reducing the arsenic pressure during the InAs growth. When these growth conditions are not respected, the multicomponent photoluminescence spectrum obtained is explained through the common interpretation of island height varying with monolayer fluctuation. In optimized growth conditions, the multicomponent spectrum obtained is interpreted as emission from fundamental and excited levels of InAs islands with low height dispersion. Transmission electron microscopy (TEM) imaging shows that these InAs islands are stick-like, 50–100 nm in length and 22±1.2 nm in width. Cross-sectional TEM reveals f...

Effect of HCl on the doping and shape control of silicon nanowires

Abstract: The introduction of hydrogen chloride during the in situ doping of silicon nanowires (SiNWs) grown using the vapor-liquid-solid (VLS) mechanism was investigated. Compared with non-chlorinated atmospheres, the use of HCl with dopant gases considerably improves the surface morphology of the SiNWs, leading to extremely smooth surfaces and a greatly reduced tapering. Variations in the wire diameter are massively reduced for boron doping, and cannot be measured at 600 °C for phosphorous over several tens of micrometers. This remarkable feature is accompanied by a frozen gold migration from the catalyst, with no noticeable levels of gold clusters observed using scanning electron microscopy. A detailed study of the apparent resistivity of the NWs reveals that the dopant incorporation is effective for both types of doping. A graph linking the apparent resistivity to the dopant to silane dilution ratio is built for both types of doping and discussed in the frame of the previous results.

Silicon nanowires: Diameter dependence of growth rate and delay in growth

Abstract: We grew Si nanowires by chemical vapor deposition, via the vapor liquid solid growth, using silane as gaseous precursor and gold as catalyst. The results show that the nanowire length depends on their diameter. For nanowires with diameter under 100 nm, the length increases when diameter increases, because of an increase in the growth velocity. For the thicker diameter (d>100 nm), length decreases when diameter increases, due to an apparent incubation time which is all the higher as the diameter is high. We propose a semiempirical model combining Gibbs–Thomson effect and incubation time, which shows good agreement with the experimental data.

Surface recombination velocity measurements of efficiently passivated gold-catalyzed silicon nanowires by a new optical method.

Abstract: The past decade has seen the explosion of experimental results on nanowires grown by catalyzed mechanisms. However, few are known on their electronic properties especially the influence of surfaces and catalysts. We demonstrate by an optical method how a curious electron−hole thermodynamic phase can help to characterize volume and surface recombination rates of silicon nanowires (SiNWs). By studying the electron−hole liquid dynamics as a function of the spatial confinement, we directly measured these two key parameters. We measured a surface recombination velocity of passivated SiNWs of 20 cm s−1, 100 times lower than previous values reported. Furthermore, the volume recombination rate of gold-catalyzed SiNWs is found to be similar to that of a high-quality three-dimensional silicon crystal; the influence of the catalyst is negligible. These results advance the knowledge of SiNW surface passivation and provide essential guidance to the development of efficient nanowire-based devices.

Ion and electron irradiation-induced effects in nanostructured materials

Abstract: A common misconception is that the irradiation of solids with energetic electrons and ions has exclusively detrimental effects on the properties of target materials. In addition to the well-known cases of doping of bulk semiconductors and ion beam nitriding of steels, recent experiments show that irradiation can also have beneficial effects on nanostructured systems. Electron or ion beams may serve as tools to synthesize nanoclusters and nanowires, change their morphology in a controllable manner, and tailor their mechanical, electronic, and even magnetic properties. Harnessing irradiation as a tool for modifying material properties at the nanoscale requires having the full microscopic picture of defect production and annealing in nanotargets. In this article, we review recent progress in the understanding of effects of irradiation on various zero-dimensional and one-dimensional nanoscale systems, such as semiconductor and metal nanoclusters and nanowires, nanotubes, and fullerenes. We also consider the t...

Nanowire Solar Cells

Abstract: The nanowire geometry provides potential advantages over planar waferbased or thin-film solar cells in every step of the photoconversion process. These advantages include reduced reflection, extreme light trapping, improved band gap tuning, facile strain relaxation, and increased defect tolerance. These benefits are not expected to increase the maximum efficiency above standard limits; instead, they reduce the quantity and quality of material necessary to approach those limits, allowing for substantial cost reductions. Additionally, nanowires provide opportunities to fabricate complex single-crystalline semiconductor devices directly on low-cost substrates and electrodes such as aluminum foil, stainless steel, and conductive glass, addressing another major cost in current photovoltaic technology. This review describes nanowire solar cell synthesis and fabrication, important characterization techniques unique to nanowire systems, and advantages of the nanowire geometry.

A Review of Mechanical and Electromechanical Properties of Piezoelectric Nanowires

Abstract: Piezoelectric nanowires are promising building blocks in nanoelectronic, sensing, actuation and nanogenerator systems. In spite of great progress in synthesis methods, quantitative mechanical and electromechanical characterization of these nanostructures is still limited. In this article, the state-of-the art in experimental and computational studies of mechanical and electromechanical properties of piezoelectric nanowires is reviewed with an emphasis on size effects. The review covers existing characterization and analysis methods and summarizes data reported in the literature. It also provides an assessment of research needs and opportunities. Throughout the discussion, the importance of coupling experimental and computational studies is highlighted. This is crucial for obtaining unambiguous size effects of nanowire properties, which truly reflect the effect of scaling rather than a particular synthesis route. We show that such a combined approach is critical to establish synthesis-structure-property relations that will pave the way for optimal usage of piezoelectric nanowires.

Review of terahertz photoconductive antenna technology

Abstract: Photoconductive antennas (PCAs) have been extensively utilized for the generation and detection of both pulsed broadband and single frequency continuous wave terahertz (THz) band radiation. These devices form the basis of many THz imaging and spectroscopy systems, which have demonstrated promising applications in various industries and research fields. The development of THz PCA technology through the last 30 years is reviewed. The key modalities of improving device performance are identified, and literature is reviewed to summarize the progress made in these areas. The goal of this review is to provide a collection of all relevant literature to bring researchers up to date on the current state and remaining challenges of THz PCA technology.