A.M. Piro

Optical and structural properties of Er2O3 films grown by magnetron sputtering

The structural properties and the room temperature luminescence of Er2O3 thin films deposited by magnetron sputtering have been studied. In spite of the well-known high reactivity of rare earth oxides towards silicon, films characterized by good morphological properties have been obtained by using a SiO2 interlayer between the film and the silicon substrate. The evolution of the properties of the Er2O3 films due to thermal annealing processes in oxygen ambient performed at temperatures in the range of 800–1200°C has been investigated in detail. The existence of well defined annealing conditions (rapid treatments at a temperature of 1100°C or higher) allowing to avoid the occurrence of extensive chemical reactions with the oxidized substrate has been demonstrated; under these conditions, the thermal process has a beneficial effect on both structural and optical properties of the film, and an increase of the photoluminescence (PL) intensity by about a factor of 40 with respect to the as-deposited material has been observed. The enhanced efficiency of the photon emission process has been correlated with the longer lifetime of the PL signal. Finally, the conditions leading to a reaction of Er2O3 with the substrate have been also identified, and evidences about the formation of silicate-like phases have been collected.The structural properties and the room temperature luminescence of Er2O3 thin films deposited by magnetron sputtering have been studied. In spite of the well-known high reactivity of rare earth oxides towards silicon, films characterized by good morphological properties have been obtained by using a SiO2 interlayer between the film and the silicon substrate. The evolution of the properties of the Er2O3 films due to thermal annealing processes in oxygen ambient performed at temperatures in the range of 800–1200°C has been investigated in detail. The existence of well defined annealing conditions (rapid treatments at a temperature of 1100°C or higher) allowing to avoid the occurrence of extensive chemical reactions with the oxidized substrate has been demonstrated; under these conditions, the thermal process has a beneficial effect on both structural and optical properties of the film, and an increase of the photoluminescence (PL) intensity by about a factor of 40 with respect to the as-deposited material h...

Activation and carrier mobility in high fluence B implanted germanium

High doping regimes of B implanted Ge have been accurately characterized combining Hall effect technique and nuclear reaction analysis. Preamorphized Ge was implanted with B at 35keV (spanning the 0.25–25×1020B∕cm3 concentration range) and recrystallized by solid phase epitaxy at 360°C. The Hall scattering factor and the maximum concentration of active B resulted rH=1.21 and ∼5.7×1020B∕cm3, respectively. The room-temperature carrier mobility was accurately measured, decreasing from ∼300to50cm2∕Vs in the investigated dopant density, and a fitting empirical law is given. These results allow reliable evaluation for Ge application in future microelectronic devices.

Ion irradiation-induced local structural changes in amorphous Ge2Sb2Te5 thin film

The crystallization kinetics of as-deposited and ion implanted amorphous Ge2Sb2Te5 thin films has been measured by time resolved reflectivity. An enhancement of the crystallization process occurred in the implanted samples. Raman scattering analysis was used to correlate the stability of the amorphous phase to its structure. The variation of the Raman signal after ion irradiation is consistent with a reduction in Ge–Te tetrahedral bonds, characteristic of the Ge coordination in amorphous Ge2Sb2Te5.

B activation and clustering in ion-implanted Ge

Experimental studies about electrical activation and clustering of B implanted in crystalline Ge (c-Ge) are reported. To this aim, we structurally and electrically investigated c-Ge samples implanted at different temperatures with B at 35 keV in the high-concentration dopant regime (0.67–25×1020 B/cm3). We elucidated that a high level of damage, in the form of amorphous pockets, favors the electrical activation of the dopant, and a complete activation was achieved for properly chosen implant conditions. We found, by joining channeling measurements with the electrical ones, that the reason for incomplete B activation is the formation of B-Ge complexes with a well-defined stoichiometry of 1:8. The thermal stability of the B-doped samples, up to 550 °C, was also investigated. The tested stability demonstrates that the B clustering, responsible of B inactivity, is characterized by high binding energies and higher thermal budgets are needed to make them to dissolve. These studies, besides clarify the physical ...

The influence of stoichiometry on the structural stability and on the optical emission of erbium silicate thin films

We report the effects of thermal annealing performed in N2 or O2 ambient at 1200°C on the structural and optical properties of Er silicate films having different compositions (Er2SiO5, Er2Si2O7, and their mixture). We demonstrate that the chemical composition of the stoichiometric films is preserved after the thermal treatments. All different crystalline structures formed after the thermal annealing are identified. Thermal treatments in O2 lead to a strong enhancement of the photoluminescence intensity, owing to the efficient reduction of defect density. In particular the highest optical efficiency is associated to Er ions in the α phase of Er2Si2O7.

Room-temperature boron displacement in crystalline silicon induced by proton irradiation

The effect induced by proton irradiation on B-doped crystalline Si at room temperature is investigated in detail. The displacement of B atoms out of substitutional lattice sites is shown to be induced at room temperature by proton irradiation at energies ranging between 300 and 1300 keV. This phenomenon was studied by means of channeling and nuclear reaction analysis techniques using the B11(p,α)Be8 nuclear reaction at 650 keV proton energy. For all the irradiation energies used, the fraction of displaced B atoms increases exponentially with proton irradiation fluence until saturation occurs. The B displacement rate strongly increases by decreasing the irradiation energy. We show that B off-lattice displacement is not due to a direct interaction of the proton beam with B atoms, but to the Si self-interstitials (ISi) generated in the lattice by the irradiating beam. The displacement results from the formation of a mobile B-ISi pair when a ISi is trapped by a substitutional B. The measured damage rate has b...

Fluorine counter doping effect in B-doped Si

We investigated the effect of F on the electrical activity of B-doped junctions in preamorphized Si. It is shown that while the carrier dose introduced by B is reduced in the presence of F, no indication of B–F complexes formation can be found and B maintains its full substitutionality. Investigations on F-enriched crystalline Si demonstrated and quantified the n-type doping of F. These results clarify that the loss of holes in junctions coimplanted with B and F is not due to a chemical interaction between B and F, but simply to a dopant compensation effect.

Detailed arsenic concentration profiles at Si/SiO2 interfaces

The pile-up of arsenic at the Si/SiO2 interface after As implantation and annealing was investigated by high resolution Z-contrast imaging, electron energy-loss spectroscopy (EELS), grazing incidence x-ray fluorescence spectroscopy (GI-XRF), secondary ion mass spectrometry, x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, as well as Hall mobility and four-point probe resistivity measurements. After properly taking into account their respective artifacts, the results of all methods are compatible with each other, with EELS and GI-XRF combined with etching providing similar spatial resolution on the nanometer scale for the dopant profile. The sheet concentration of the piled-up As at the interface was found to be ∼1×1015 cm−2 for an implanted dose of 1×1016 cm−2 with a maximum concentration of ∼10 at. %. The strain observed in the Z-contrast images also suggests a significant concentration of local distortions within 3 nm from the interface, which, however, do not seem to involve in...

Thermal evolution of Er silicate thin films grown by rf magnetron sputtering

Stoichiometric Er silicate thin films, monosilicate (Er2SiO5) and disilicate (Er2Si2O7), have been grown on c-Si substrates by rf magnetron sputtering. The influence of annealing temperature in the range 1000–1200 °C in oxidizing ambient (O2) on the structural and optical properties has been studied. In spite of the known reactivity of rare earth silicates towards silicon, Rutherford backscattering spectrometry shows that undesired chemical reactions between the film and the substrate can be strongly limited by using rapid thermal treatments. Monosilicate and disilicate films crystallize at 1100 and 1200 °C, respectively, as shown by x-ray diffraction analysis; the crystalline structures have been identified in both cases. Moreover, photoluminescence (PL) measurements have demonstrated that the highest PL intensity is obtained for Er2Si2O7 film annealed at 1200 °C. In fact, this treatment allows us to reduce the defect density in the film, in particular by saturating oxygen vacancies, as also confirmed by the increase of the lifetime of the PL signal.

Synthesis of crystalline Si quantum dots by millisecond laser irradiation of SiOxNy layers

We demonstrated that the timescale for Si quantum dot (Si-QD) formation in a SiOxNy layer is a few milliseconds by IR laser irradiation. The amount of Si agglomerated into QD in a laser irradiated SiOxNy layer is comparable to that calculated after furnace annealing at 1250 °C for 30 min. However, we found that crystalline Si-QD can be formed by laser only if the amount of Si atoms in excess is as high as 1×1022/cm3. The Si-QD contains impurities like N and O that prevent luminescence at 900 nm. The photoluminescence (PL) signal is recorded only after an additional annealing after laser irradiation at temperatures above 1000 °C when diffusion-assisted replacement of N and O occurs.