J.J. Grob

Silicon solar cells realized by laser induced diffusion of vacuum‐deposited dopants

A technique for solar cell preparation based on vacuum deposition of thin films of dopants on silicon, followed by irradiation with a high‐energy (∼1.5 J/cm2) ruby laser pulse is described. Several dopants like phosphorus, antimony, bismuth, aluminium, gallium, and indium have been investigated. Electrical and Rutherford backscattering measurements indicate that the dopant is dissolved in the silicon and becomes electrically active, as a result of the irradiation. The P‐N junctions which are formed are shallow (depth <4000 A) but heavily doped, since after the laser treatment the solubility of the dopant is generally higher than after a thermal diffusion. Therefore good diode characteristics can be achieved by this simple method, and solar cells up to 14 % efficiency under AM1 (air mass 1) illumination have been realized using dopants like phosphorus, antimony, bismuth, aluminium, or gallium.

Structural and electrical properties of Ge nanocrystals embedded in SiO2 by ion implantation and annealing

Silicon dioxide (SiO2) on Si layers with embedded germanium nanocrystals (Ge-ncs) were fabricated using Ge+ implantation and subsequent annealing. Transmission electron microscopy and Rutherford backscattering spectrometry have been used to study the Ge redistribution in the SiO2 films as a function of annealing temperature. A monolayer of Ge-ncs near the Si∕SiO2 interface was formed under specific annealing conditions. This layer, with a nc density and mean size measured to be, respectively, 1.1×1012∕cm2 and 5nm, is located at approximately 4nm from the Si∕SiO2 interface. Capacitance–voltage measurements were performed on metal-oxide-semiconductor structures containing such implanted SiO2 layers in order to study their electrical properties. The results indicate a strong memory effect at relatively low programming voltages (<5V) due to the presence of Ge-ncs near the Si∕SiO2 interface.

Stimulated emission in blue-emitting Si+-implanted SiO2 films?

We investigate the blue photoluminescence of Si+-implanted SiO2 films under picosecond UV excitation. The emission intensity exhibits a nonlinear increase with increasing excitation intensities, accompanied by pulse shortening. The photoluminescence decays nonmonoexponentially in time. However, the nonlinearities are not associated with significant spectral narrowing. To explain the results, we propose and numerically investigate a kinetic model based on competition between radiative (both spontaneous and stimulated) and nonradiative recombination in isolated luminescence centers in the SiO2 matrix. Good agreement between theoretical and experimental data seems to confirm the existence of stimulated emission in the films, however, under extremely high excitation densities only (approximately 100 MW/cm2).

Formation of thin silicon oxide films by rapid thermal heating

Rapid thermal heating of silicon samples in a dry O2 ambient has been used to form thin SiO2 films. Compared to conventional furnace oxidation, an increased growth rate was observed which is linearly dependent on the square root of time. Activation energies of 1.99 and 2.26 eV for 〈111〉 and 〈100〉 orientation, respectively, have been determined in the range 1000–1200 °C.

Effects of high energy nitrogen implantation on stainless steel microstructure

Abstract Low energy ion implantation is known to improve chemical and mechanical surface properties of metals. This treatment is often used to enhance wear and corrosion resistance or mechanical life-time of fatigue test of stainless steel or titanium alloys. The aim of this work is to investigate these effects at higher energy, for which deeper (and still not well understood) modifications occur. High fluence (1018 cm−2) 15N and 14N implantations at 1 MeV have been performed in the 316LL stainless steel and some specimen have been annealed in the 200–500°C temperature range. Nitrogen concentration distribution, structure, morphology and microhardness have been examined with Nuclear Resonance Analysis, Grazing Incidence X-Ray Diffraction and Nanoindentation, respectively. Precipitates of steel and chromium nitride phases and a superficial martensitic transformation can be observed, leading to a significant increase of hardness. The best result is obtained after one hour annealing at 425°C, due to a larger and more homogeneous repartition of nitride species. In this case, a near surface accumulation is observed and explained in terms of diffusion and precipitation mechanisms.

Effect of high energy argon implantation into NiTi shape memory alloy

Abstract The super-elastic properties of NiTi alloy are used for several medical applications in dentistry, such as orthodontic wires (useful to correct the dental position), palatal expanders and endodontic instruments. Implantation process may be one solution to enhance the surface properties, corrosion, wear and fatigue resistance, of such instruments. A previous work, for which implantations were performed with N + and B + ions at 150 keV, has shown that the hardening mechanism is due to the formation of an amorphous layer whose thickness increased with dose in the near surface region. In this paper, in order to increase the treated thickness, especially the amorphous layer, argon implantations at high energy (1.5 MeV) have been performed. The structural modifications have been observed with Grazing Incidence X-ray Diffraction (GIXRD), as a function of Ar + dose. The processes involved in the crystalline to amorphous phase transformation of NiTi under ion beam irradiation have been particularly investigated. Characterisation of the near surface composition was made by Rutherford Backscattering Spectroscopy (RBS). Nanoindentation tests have been used to study the evolutions of hardness and elastic modulus through the treated thickness after implantation.

Structure and magnetic properties of Co+-implanted silica

Abstract Cobalt has been implanted at 30 and 160 keV in three different silica-based substrates. TEM observations and magnetization measurements performed at RT and 5 K show that, after implantation, cobalt is present both as metal particles, few nanometers in size and as smaller oxide particles. Optical absorption measurements show that the presence of oxide particles is linked to the formation of Si–Si bonds during implantation. After thermal treatment under hydrogen, cobalt is entirely in the metallic form and saturation magnetization becomes close to its theoretical value. Last, the initial amount of oxide depends on the OH− content of the substrate.

Nuclear reaction analysis of helium diffusion in britholite

We have derived the helium bulk diffusion constants in britholite (Ca9Nd(PO4)5(SiO4)F2) from non-destructive 3He depth profiling using the resonant 3He(d, p)4He nuclear reaction. Results have been obtained on a polycrystalline sintered ceramics implanted with 3 MeV 3He+ ions at a depth around 9 μm then annealed in air at temperatures between 200 and 400 °C. The activation energy for helium diffusion is around 1.1 eV. These data are in good agreement with literature data based on ERDA depth profiling of 27 keV 4He+ ions implanted in natural (Durango) or synthetic fluorapatite single crystals.

Retention in metal-oxide-semiconductor structures with two embedded self-aligned Ge-nanocrystal layers

Structural and electrical characterization has been carried out on metal–oxide–semiconductor (MOS) structures with a silicon dioxide (SiO2) layer containing a germanium nanocrystals (Ge-ncs) floating gate. Ge-nc layers were embedded in SiO2 by ion implantation with subsequent annealing. Structural analysis proved the presence of two self-aligned nanocrystal layers within the SiO2 host material. The electrical results indicate a strong memory effect due to the presence of a near-interface Ge-nc layer. Few volts memory windows can easily be obtained at relatively low programming voltages (<6 V). For comparison, operating voltages used in current FLASH technology are about 12 V. Despite its promising structural properties, retention times extracted from capacitance measurements and scanning Kelvin microscopy were found to be too low (~105 s) to comply with the non-volatility industry requirements (<10 years required).

Laser‐beam annealing of heavily damaged implanted layers on silicon

The behavior during annealing of heavily doped silicon layers obtained by a high‐current‐density ion implantation, realized by discharge in BF3 atmosphere, is investigated. The annealing is performed by a laser pulse and the surface layers are studied by Rutherford backscattering, SIMS, and conductivity measurements. Comparisons with thermal annealing show the advantage of using laser pulses to restore the original crystallinity.