A Combined Ion Implantation/Nanosecond Laser Irradiation Approach towards Si Nanostructures Doping

The exploitation of Si nanostructures for electronic and optoelectronic devices depends on their electronic doping. We investigate a methodology for As doping of Si nanostructures taking advantages of ion beam implantation and nanosecond laser irradiation melting dynamics. We illustrate the behaviour of As when it is confined, by the implantation technique, in a SiO2/Si/SiO2multilayer and its spatial redistribution after annealing processes. As accumulation at the Si/SiO2interfaces was observed by Rutherford backscattering spectrometry in agreement with a model that assumes a traps distribution in the Si in the first 2-3 nm above the SiO2/Si interfaces. A concentration of 1014 traps/cm2has been evaluated. This result opens perspectives for As doping of Si nanoclusters embedded in SiO2since a Si nanocluster of radius 1 nm embedded in SiO2should trap 13 As atoms at the interface. In order to promote the As incorporation in the nanoclusters for an effective doping, an approach based on ion implantation and nanosecond laser irradiation was investigated. Si nanoclusters were produced in SiO2layer. After As ion implantation and nanosecond laser irradiation, spectroscopic ellipsometry measurements show nanoclusters optical properties consistent with their effective doping

Crystallization properties of melt-quenched Ge-rich GeSbTe thin films for phase change memory applications

The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements. The optical properties have been related to the structure and composition by means of the effective medium approximation. The compositional variations have been investigated by transmission electron microscopy and electron energy loss spectroscopy. Amorphous materials prepared by melt-quenching with different laser energy densities have been studied. For the energy density of 1.5 J cm−2, a uniform amorphous layer, with embedded Ge crystalline grains, is obtained. The film exhibits a crystallization temperature of 275 °C and no relevant phase separation during crystallization. For a lower energy density of 1 J cm−2, only half of the film thickness is quenched to the amorphous phase, with Ge depletion. The crystallization temperature of the Ge depleted film is 245 °C, and a partial phase separation occurs

Infrared photovoltaic detector based on p-GeTe/n-Si heterojunction

GeTe is an important narrow bandgap semiconductor material and has found application in the fields of phase change storage as well as spintronics devices. However, it has not been studied for application in the field of infrared photovoltaic detectors working at room temperature. Herein, GeTe nanofilms were grown by magnetron sputtering technique and characterized to investigate its physical, electrical, and optical properties. A high-performance infrared photovoltaic detector based on GeTe/Si heterojunction with the detectivity of 8 × 1011 Jones at 850 nm light irradiation at room temperature was demonstrated

Rayleigh-instability-driven dewetting of thin Au and Ag films on indium-tin-oxide surface under nanosecond laser irradiations

Investigations have been carried out on laser-beam-induced nanoparticle (NP) formation in thin (5 nm) Au and Ag films on indium-tin-oxide substrate. After the irradiation the films were observed to break-up into NPs through a dewetting mechanism. This mechanism was investigated as a Rayleigh-instability- driven process. In fact, for each used laser fluence, the resulting Au and Ag NPs' mean size and surface-to-surface mean distance were quantified and correlated between them in the framework of the Rayleigh-instability theory showing an excellent agreement. © The Institution of Engineering and Technology 2013

High-level incorporation of antimony in germanium by laser annealing

In this work we investigate pulse laser annealing as an alternative approach to reach high-level incorporation of Sb in substitutional location in crystalline germanium. Laser irradiation is demonstrated to recover also those structural defects, like honeycomb structures, that form during high-fluence heavy-ion implantations in Ge and that cannot be eliminated by conventional thermal treatments. Indeed, concentrations of substitutional Sb higher than 1 71021\u2002at./cm3 have been obtained, well above the solid solubility of Sb in Ge. The strain induced on the Ge host lattice is also investigated, evidencing that the obtained Sb doped Ge layer is pseudomorphic to the Ge substrate while positively strained by the substitutional Sb atoms present within the Ge matrix. The kinetics of this Sb-rich Ge alloy phase is finally investigated, showing that most of Sb goes out of lattice with increasing the annealing temperature up to 488\u2009\ub0C, leading to a decrease in the related lattice deformation. These results are very relevant for the future high-mobility channel technology

Nanostructuring thin Au films on transparent conductive oxide substrates

Fabrication processes of Au nanostructures on indium-tin-oxide (ITO) surface by simple, versatile, and low-cost bottom-up methodologies are investigated in this work. A first methodology exploits the patterning effects induced by nanosecond laser irradiations on thin Au films deposited on ITO surface. We show that after the laser irradiations, the Au film break-up into nanoclusters whose mean size and surface density are tunable by the laser fluence. A second methodology exploits, instead, the patterning effects of standard furnace thermal processes on the Au film deposited on the ITO. We observe, in this case, a peculiar shape evolution from pre-formed nanoclusters during the Au deposition stage on the ITO, to holed nanostructures (i.e. nanorings), during the furnace annealing processes. The nanorings depth, height, width, and surface density are shown to be tunable by annealing temperature and time. © 2012 Elsevier B.V. All rights reserved

Role of the strain in the epitaxial regrowth rate of heavily doped amorphous Si films

Solid phase epitaxial regrowth (SPER) of p -doped preamorphized Si was studied by time resolved reflectivity. Strain and dopant concentration were opportunely varied by implanting neutral (Ge) and isovalent (B, Ga) impurities in order to disentangle the two different effects on SPER. Larger SPER rate variations occurred in strained doped Si with respect to undoped samples. The generalized Fermi level shifting model was implemented to include the role of the strain and to fit the experimental data over a large range of temperature for p - and n -type doping. We introduced a charged defect, whose energy level is independent of the dopant species. © 2008 American Institute of Physics

Formation and evolution of nanoscale metal structures on ito surface by nanosecond laser irradiations of thin Au and Ag films

The effect of nanosecond laser irradiations on 5 nm thick sputter-deposited Au and Ag films on Indium-Tin-Oxide surface is investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). After 500, 750, and 1000 mJ/cm 2 fluence irradiations, the breakup of the Au and Ag films into nanoscale islands is observed as a consequence of fast melting and solidification processes. The mean nanoparticles size and surface density are quantified, as a function of the laser fluence, by the AFM and SEM analyses. In particular, the comparison between the Au and Ag islands reveals the formation of larger islands in the case of Ag for each fixed fluence. The mechanism of the nanoscale islands formation is discussed, both for Au and Ag, in terms of the starting film thickness fluctuations (influencing the local threshold for melting), dewetting phenomenon and the Rayleigh criterion. © 2012 by American Scientific Publishers

Crystallization of ion amorphized Ge2Sb2Te5 thin films in presence of cubic or hexagonal phase

The crystallization kinetics of amorphous Ge2Sb2Te5 (GST) thin films, generated by ion implantation, on top of crystalline GST, either in the cubic or hexagonal phase, was investigated by means of time resolved reflectivity measurements, x-ray diffraction, in situ transmission electron microscopy, and Raman analyses. The crystallization occurred at a lower temperature with respect to a fully amorphous film and in both cases the crystalline phase started growing at the underlying amorphous-crystalline (a-c) interface. However, it was not a solid phase epitaxial growth since cubic GST was always obtained, independent of the phase of the underlying crystal. We speculate that the a-c interface behaves as a continuous region of potential nucleation sites in the crystallization making the crystallization process more efficient