ANALYSIS AND ORIGIN OF POINT DEFECTS IN SILICON AFTER LIQUID PHASE TRANSIENT ANNEALING

Works devoted to the study of point defects in pulsed laser annealed silicon are reviewed by means of electrical characterization. Tailing effects of the implanted distribution are responsible for the observed residual defects in the case of a layer amorphized by ion implantation. However, difficulty in annealing some kinds of point defects by reducing the duration of laser pulse have been shown using slightly disordered silicon. Finally, in the case of irradiated virgin silicon, a high level of point defects are created, which are essentially donor levels that introduce a compensating effect in P-type silicon

ETUDE PAR MICROSCOPIE ELECTRONIQUE DE LA DIFFUSION INDUITE PAR LASER

Une étude du phénomène de diffusion induite par faisceau laser de différents dopants dans le silicium est menée par Microscopie Electronique. Des points communs sont établis entre les résultats obtenus par cette méthode et par implantation (concentration maximum en solution solide, coefficient de ségrégation, apparition d'instabilités, ...). Les paramètres expérimentaux sont choisis (épaisseur déposée, type de dopant, énergie du laser, ...) de manière à favoriser la bonne intégration du dopant dans la matrice, ou, au contraire, l'apparition de cellules de ségrégation dues aux instabilités de l'interface solide-liquide. L'étude porte sur quatre dopants (Sb, Ga, Bi, In), pour différentes épaisseurs déposées (50 à 150 A). Les résultats donnés par Microscopie sont en bon accord d'une part avec les résultats RBS, et d'autre part avec un modèle développé pour la diffusion induite par laser

Geometrical factor in multi-interface homostructures

In an experimental investigation carried out on multilayer silicon homostructures (of the n+-n-n+ type) an electric interaction between the two homointerfaces through majority carriers as a function of the geometrical factor has been shown. The two model homointerfaces were formed in the same monocrystal (CVD epitaxy) by only an abrupt change in the impurity doping level. Samples differing in the spacing of their parallel interfaces were characterized in the stationary and steady states (static and quasi-static regimes) to reveal modifications in their macroscopic transport. It has been demonstrated that the thermionic emission current, normally taken into account in the barrier transport (with large potential barriers) dominates in only two of five characteristic bias intervals. The two other phenomena, also related to the geometrical factor, i.e. the diffusion-drift and tunneling currents, dominate the conduction over practically the whole dc-bias range. These results allow the study of short and long range electrical interactions as well as the free carrier micromovement of simple and complex semiconductor interfaces of multilayer devices

SEM CHARACTERIZATION OF EFG POLYCRYSTALLINE SILICON SOLAR CELLS REALIZED BY ION IMPLANTATION AND LASER ANNEALING WITH OVERLAPPING PULSES

Atomic and molecular ion implantation (AMI) of non mass separated PF5 ions has been used to form the N+ layer on EFG ribbon. A pulsed Nd-YAG laser operating at a high repetition rate (10 kHz) was then employed to anneal the amorphized layer via liquid phase epitaxy. The properties of the recrystallized layers have been analyzed by SEM with secondary electron micrography and EBIC. The following results have been observed. At low electron beam energies (below 12 keV), strong EBIC recombination currents resulting from the overlapping laser pulses is clearly visible. At higher energies (above 20 keV), the recombination due to the grain boundaries in the ribbon becomes dominant. The regrowth after annealing replicates exactly the underlying structure. Finally, some electrical characteristics of the doped layers (doping profile) as well as the photovoltaïc performance are presented. Efficiencies up to 11 % have been obtained under AMI conditions

EFFETS DES TRAITEMENTS THERMIQUES SUR LES PROPRIETES ELECTRIQUES DES CELLULES SOLAIRES A BASE DE SILICIUM POLYCRISTALLIN

On a étudié l'effet de recuits à haute température sur les caractéristiques électriques à l'obscurité et sous éclairement de cellules solaires à base de silicium polycristallin dont la jonction était préparée à froid par incrustation ionique et recuit par laser pulsé. Dans certains cas des dégradations notables sont observées pour des recuits à 900°C

SOLUBILITY LIMIT OF DOPANTS IN SILICON IRRADIATED BY RUBY LASER

The solubility of several dopants (Sb, Ga, Bi, In) in laser treated silicon has been investigated. The dopants were introduced by vacuum deposition followed by a ruby laser irradiation. Their solubility was determined by Rutherford backscattering spectrometry measurements in channeling and random conditions. In all cases a solubility limit Cmℓ higher than the equilibrium solubility was found and a simple correlation with the equilibrium distribution coefficient kO could be established : Cmℓ = 8.6 × 1021 k0.51O cm-3

INTERACTION BETWEEN ARGON AND DOPANTS IN SPUTTERED a-Si : H

The concentrations of As, B, H, Ar and Si in sputtered a-Si : H are measured by helium Rutherford backscattering and nuclear reactions analysis. Excess or deficit of hydrogen and argon by comparison with intrinsic a-Si : H are found in presence of dopants at high deposition rate. This is related to the plasma deposition method and would suggest micro grain structure in the deposited layer

PULSED ELECTRON BEAM ANNEALING OF As AND B IMPLANTED SILICON

p-type (100) silicon wafers have been implanted either by As or B ions at 20 and 200 keV energies and doses of 1016cm-2. Pulsed electron beam annealing has been performed with fluences of 1.1 and 1.4 J/cm2 using a mean electron energy of 15 keV. The pulse duration was 50 ns. The annealed layers have been investigated by Rutherford backscattering under random and channeling conditions and by S.I.M.S. profiling. Good crystal regrowth and high dopant activation occur in all cases except for the 200 keV Boron implant. Impurities redistribution is observed but no significant segregation effects appear. The experimental profiles are in good agreement with a diffusion model using a modified green function solution and taking into account dopant diffusion in liquid phase and the computed melt front location. The deduced diffusion coefficient are in the 5.10-5cm2/s range for boron and 2.10-4cm2/s range for arsenic

Light-chain-induced renal tubular acidosis: effect of sodium bicarbonate on sodium-proton exchange

We measured sodium-proton (Na+/H+) exchange in lymphocytes and platelets of a 46-year-old woman with the adult Fanconi syndrome before, during, and after treatment with NaHCO3. Kappa light chains in her urine and unique but rarely observed crystalline structures confirmed the presence of light-chain nephropathy. Her glomerular filtration rate was only moderately impaired at 72 ml/min. NaHCO3 at 1, 3, and 5 mmol/kg/day for 5 days increased her serum HCO3 and pH from 17 to 21 mmol/l and 7.28 to 7.39 respectively. Plasma renin and aldosterone values were decreased by NaHCO3. Na+/H+ exchange (δHi/min) was measured with the fluorescent marker BCECF after acidification of lymphocytes and platelets with sodium propionate at five (10-50mM) doses. Na+/H+ exchange was accelerated in this patient compared to normal controls. NaHCO3 treatment significantly decreased Na+/H+ exchange in lymphocytes, but not in platelets. These findings suggest that Na+/H+ exchange can be influenced by NaHCO3 ingestion at doses that only modestly affect systemic pH. Since Na+/H+ exchange is involved in stimulus response coupling, cell growth regulation, cell differentiation, and perhaps the progression of nephrosclerosis, these observations may have clinical relevanc

Characterization of charge collection in CdTe and CZT using the transient current technique

The charge collection properties in different particle sensor materials with respect to the shape of the generated signals, the electric field within the detector, the charge carrier mobility and the carrier lifetime are studied with the transient current technique (TCT). Using the well-known properties of Si as a reference, the focus is laid on Cadmium-Telluride (CdTe) and Cadmium-Zinc-Telluride (CZT), which are currently considered as promising candidates for the efficient detection of X-rays. All measurements are based on a transient-current technique (TCT) setup, which allows the recording of current pulses generated by an 241Am alpha-source. These signals will be interpreted with respect to the build-up of space-charges inside the detector material and the subsequent deformation of the electric field. Additionally the influence of different electrode materials (i.e. ohmic or Schottky contacts) on the current pulse shapes will be treated in the case of CdTe. Finally, the effects of polarization, i.e. the time-dependent degradation of the detector signals due to the accumulation of fixed charges within the sensor, are presented.Comment: 20 pages, 17 figure