Lazhar Haji

Poly-Si Thin Film Transistors Fabricated with Rapid Thermal Annealed Silicon Films

This letter describes a new process for realization of polysilicon thin-film transitors (TFT) on glass substrates. The process is based on crystallization by rapid thermal annealing of amorphous silicon films deposited by low-pressure chemical vapor deposition (LPCVD). With this technique, the time of crystallization of the silicon films is reduced to a few seconds. Thin-film transistors have been realized using this process, and the field-effect mobility is in the range of 20 cm2V-1s-1.

Porosity Gradient Resulting from Localised Formation of Porous Silicon: The Effect on Waveguiding

Porous silicon formation on patterned substrates leads to a depth-dependent porosity. These porosity variations depend on the anodisation parameters and on the size of the open windows in the masking layer. During the anodisation at a constant current intensity, the interfacial reaction area increases and consequently the porosity decreases. Moreover, the porous silicon growth rate depends on crystallographic directions and induces a porosity gradient along the core/cladding interface. These porosity gradients could be crucial in some applications such as optical waveguides. Oxidised porous silicon waveguides were fabricated through a masking layer by applying two constant current intensities during anodisation. The measured near field distribution reveals that the light propagation is localised near the core/cladding interface. These observations confirm that a porosity gradient exists along vertical cross section of waveguides. This study deals with the porosity gradient estimations resulting from the electrochemical etching through an opened window in a masking layer.

Optical gain measurements in porous silicon planar waveguides codoped by erbium and ytterbium ions at 1.53μm

The on-off optical gain measurements as a function of the pump power were performed on porous silicon planar waveguides codoped by erbium and ytterbium ions. These measurements were obtained for different ratios of Yb concentration to Er concentration. The highest value of the gain was reached when the Yb concentration is three times higher than that of Er at a moderate 980nm pump power value equal to 70mW. Optical losses measurements have been performed on these waveguides and were equal to 2.1dB∕cm and an internal gain of about 6.4dB∕cm was obtained.

Substrate Effects on the Kinetics of Solid Phase Crystallization In a -Si

The effect of substrate nature on the solid phase crystallization at 600 °C of a -Si deposited by low pressure chemical vapor deposition is investigated by x-ray diffraction and transmission electron microscopy. The nucleation rate varies slightly resulting to a weak variation in the final grain sizes as a function of the substrate type. In all cases the grain growth mode is found to be three dimensional. In contrary, a drastic effect of the substrate is observed for films deposited by plasma enhanced CVD. Fast crystallization is obtained on indium tin oxide (ITO) resulting to small grain poly-Si, whereas the crystallization is retarded on glass leading to an increase in the grain size.

Anti resonant reflecting optical waveguide structure based on oxidized porous silicon for label free bio sensing applications

In this letter we report on the use of an electrochemical process for the fabrication of anti resonant reflecting optical waveguide based on oxidized porous silicon. This method is known to allow the formation of various photonic structures (Bragg mirror, microcavity), thanks to the easy and in situ modulation of the porosity and thus of the refractive index. Planar anti resonant reflecting optical waveguide structure made from porous silicon is demonstrated to be very effective for low losses as compared to conventional resonant waveguide. Optical measurements carried out for TE and TM polarizations are reported and related to optical sensing.

Buried anti resonant reflecting optical waveguide based on porous silicon material for an integrated Mach Zehnder structure

A buried anti resonant reflecting optical waveguide for an integrated Mach Zehnder structure based on porous silicon material is achieved using a classical photolithography process. Three distinct porous silicon layers are then elaborated in a single step, by varying the porosity (thus the refractive index) and the thickness while respecting the anti-resonance conditions. Simulations and experimental results clearly show the antiresonant character of the buried waveguides. Significant variation of the reflectance and light propagation with different behavior depending on the polarization and the Mach Zehnder dimensions is obtained. Finally, we confirm the feasibility of this structure for sensing applications.

Lateral solid phase crystallization of amorphous Si induced by patterned indium tin oxide on a glass substrate

Undoped amorphous silicon films were deposited by plasma‐enhanced chemical vapor deposition on patterned indium tin oxide (ITO) onto glass substrate. The solid‐phase crystallization of these films, after successive annealing at 500 and 600 °C, was studied by optical and transmission electron microscopy. It was found that nucleation occurs very quickly on ITO and slowly on glass. The ITO patterns act as nucleation centers for grains which laterally grow and the crystalline phase spread over the glass. Results are compared with those obtained from silicon films deposited by low pressure chemical vapor deposition.

Vickers microhardness of oxidized and nonoxidized porous silicon

In this work we present our recent investigation on characterizing mechanical properties of porous silicon (PS) by using instrumented micro-indentation. Hardness and elastic modulus for oxidized and nonoxidized PS were measured. Experimental results revealed that hardness and elastic modulus are significantly lower than that of silicon substrate and decrease with increasing porosities. After oxidation an increase of the hardness and elastic modulus were observed. The task of stabilization of PS mechanical parameters can be solved with the help of oxidation.