A. Slaoui

Ex situ prepared Si nanocrystals embedded in silica glass: Formation and characterization

In this article we present an alternative approach for the fabrication of silicon nanocrystals (Si–nc) prepared ex situ of the silicon dioxide (SiO2) host matrix. The Si–nc are scratched from porous silicon layers and incorporated into a host spin-on-glass SiO2 based matrix. High-resolution transmission electron microscopy and Raman spectroscopy revealed Si–nc of 2–5 nm size. These nanocrystallites exhibit visible room temperature photoluminescence (PL) with a maximum at about 700 nm. The presence of the dopant in the host matrix is shown to induce a blueshift of the PL maxima due to modified surface states of the Si–nc. This approach allows the fabrication of self-supporting samples with very high Si–nc concentrations. A bright photoluminescence at room temperature is obtained on such materials. Finally, strong indication of optical gain at room temperature is shown for samples with high Si–nc concentrations in a phosphorus doped sol gel host matrix.

Structural, optical, and electrical properties of Yb-doped ZnO thin films prepared by spray pyrolysis method

Yb-doped ZnO thin films were prepared on glass substrates by spray pyrolysis technique in order to investigate the insertion of Yb ions in the ZnO matrix and the related optical properties of the films. The molar ratio of Yb in the spray solution was varied in the range of 0–5 at. %. X-ray diffraction patterns showed that the undoped and Yb-doped ZnO films exhibit the hexagonal wurtzite crystal structure with a preferential orientation along [002] direction. No secondary phase is observed in Yb-doped ZnO films. All films exhibit a transmittance between 75 and 90% in the visible range with a sharp absorption onset about 375 nm corresponding to the fundamental absorption edge at 3.3 eV. The photoluminescence measurements show a clear luminescence band at 980 nm that is characteristic of Yb3+ transition between the electronic levels F25/2 and F27/2. This is an experimental evidence for an efficient energy transfer from ZnO matrix to Yb3+. Hall effect measurements showed low resistivities and high carrier mob...

Molecular hydrogen formation in hydrogenated silicon nitride

Hydrogen is released from hydrogenated silicon nitride (SiNx:H) during thermal treatments. The formation of molecular hydrogen (H2) in SiNx:H layers with low mass density is confirmed by Raman spectroscopy. However, no H2 is observed in layers with a high mass density despite clear evidence that hydrogen diffuses through those layers. Therefore hydrogen migrates in those layers in a different form. This is consistent with the observed improvement of the hydrogen passivation of silicon substrates using thermally treated high density SiNx:H antireflection coatings.

LOW-TEMPERATURE SYNTHESIS OF SILICON OXIDE, OXYNITRIDE, AND NITRIDE FILMS BY PULSED EXCIMER LASER ABLATION

Silicon oxide, oxynitride, and nitride films are deposited, at low temperature (≤450 °C) by pulsed ArF excimer laser ablation from silicon, silicon monoxide, fused silica, and silicon nitride targets, performed under vacuum and in an oxygen atmosphere. The specific influence of laser fluence, target materials, substrate temperature, and oxygen pressure on the composition and final properties of SiOxNy grown layers is investigated using various complementary experiments such as infrared optical absorption, Rutherford backscattering, Auger electron spectroscopy, ellipsometry, and scanning electron microscopy. The process conditions are optimized in order to deposit good quality silicon oxide and silicon nitride thin films.

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.

Structural and photoluminescence properties of ZnO thin films prepared by sol-gel process

The present study focuses on the structural and optical properties of ZnO thin films fabricated by sol-gel process and spin coated onto Si (100) and quartz substrates. The ZnO films have a hexagonal wurtzite structure with a grain size of about 50 nm. The x-ray photoelectron spectroscopy measurements reveal the presence of Zn2+ and of zinc hydroxyl groups at the film. Optical properties were studied by photoluminescence (PL) and absorption spectroscopy at low and room temperatures. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, PL observations show two transitions: one near the absorption edge in the ultraviolet (UV) region and the second centered at 640 nm, characteristic of the deep electronic levels in the bandgap. The spectrum at 6 K is dominated by donor bound exciton lines and donor-acceptor pair transitions. LO-phonon replica and two-electron satellite transitions are also observed. These optical characteristics are a signature of g...

Phosphorus diffusion into silicon from a spin‐on source using rapid thermal processing

Diffusion of phosphorus into silicon from a doped spin‐on glass source using rapid thermal processing is described. The structural and electrical characteristics of the resulting shallow junctions including atomic and carrier concentration profiles, sheet resistance, as well as the effects on bulk carrier transport properties were studied and compared to those resulting from the use of conventional furnace heating. The results show that sheet resistance as low as 15 Ω/⧠ and surface carrier concentration higher than 1 × 1020 cm−3 are obtained in the annealed samples. Furthermore, a gettering effect is observed as the minority‐carrier diffusion length measured by the surface photovoltage technique is improved after processing.

SiO2 thin‐film deposition by excimer laser ablation from SiO target in oxygen atmosphere

Silicon dioxide thin films are deposited, for the first time, by reactive laser ablation from a silicon monoxide target in oxygen atmosphere, with a high‐power pulsed ArF (λ=193 nm) excimer laser. The specific influence of oxygen in the chamber during the laser processing on the stoichiometry and final properties of the oxide films deposited at ambient temperature is demonstrated.

Optical properties of ZnO thin films prepared by sol-gel process

The present study focused on ZnO thin films fabricated by sol-gel process and spin coated onto Si (100) and quartz substrates. ZnO thin films have a hexagonal wurtzite structure with a grain diameter about 50nm. Optical properties were determined by photoluminescence (PL) and absorption spectroscopy. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, two transitions were observed by PL. One near to the prohibited energy band in ultraviolet (UV) region and the other centered at 640nm, characteristic of the electronic defects in the band-gap. The spectrum at 6K is dominated by donor-bound exciton lines and donor-acceptor pair transition. LO-phonon replica and two-electron satellite transitions are also observed. These optical characteristics are a signature of high-quality thin films.

Pulsed laser crystallization and doping for the fabrication of high-quality poly-Si TFTs

Abstract We review the various applications of pulsed lasers, working in the nanosecond regime, to prepare high-quality poly-Si TFTs. It is shown that the best device performances (field-effect mobilities in excess of 140 cm2/V·s) are achieved by pulsed excimer laser crystallization of unhydrogenated amorphous Si thin films. In addition, for source and drain formation, we demonstrate that the excimer laser induced diffusion of dopant from a solid source (spin-on phosphorus-doped silicate glass) is very attractive to achieve good electrical properties of the n-channel TFTs.