Aomar Halimaoui

Investigation and modeling of the electrical properties of metal–oxide–metal structures formed from chemical vapor deposited Ta2O5 films

Amorphous Ta2O5 films were deposited by low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) at temperatures below 450 °C. These films were used to fabricate metal–oxide–metal (MOM) structures with titanium nitride (TiN) electrodes. The electrical properties of the MOM capacitance were investigated by the means of current–voltage and capacitance–voltage characteristics in the 100 Hz–1 MHz frequency range. It is shown that the conduction mechanism changed from Schottky emission, for the LPCVD material, to Poole–Frenkel current for the PECVD material. The roughness of the bottom electrode, as determined by atomic force microscopy measurements, is found to impact the leakage current. For the LPCVD material the capacitance exhibits a strong dependency on the applied bias and the frequency. For the PECVD material, only a small variation of the capacitance is observed when the bias is increased, with almost no frequency dependency. A clear correlation between the ...

Porous silicon strain during in situ ultrahigh vacuum thermal annealing

In situ synchrotron radiation measurements of porous silicon (PS) strain have been performed during ultrahigh vacuum (UHV) thermal annealing. For a p+ sample, the initial lattice expansion shifts toward a contraction above 270 °C in relation with hydrogen desorption. For a p− sample, the strain variation is similar to that of a p+ one, but with effects five times larger: after hydrogen desorption, the contraction strain is large (>1.5%) and inhomogeneous. In both cases, most of these strains are elastic as an HF etch re-establishes the initial expansion with a narrow diffraction peak. For p+ samples, the lattice constant exhibited a slow variation during subsequent exposure to air due to a slow oxidation of the annealed porous samples. The origin of these strain variations is discussed in relation with the presence of hydrogen or oxide coverage. The observation of similar variations in other PS properties is also discussed. Finally, the absence of a strain effect during the introduction of water vapor in ...

Covering and filling of porous silicon pores with Ge and Si using chemical vapor deposition

Filling of the pore network of porous silicon layers with Ge and Si has been demonstrated using a chemical vapor deposition (CVD) technique. It is shown that at low growth rate the species are deposited throughout the whole layer which can be completely filled. At high growth rate, the deposition takes place mainly on the top surface leading to pore mouth bridging. Investigation of the experimental data through a model shows that pore filling is a powerful tool for the study of the mechanisms involved in CVD processes at low temperature.