F. Arnaud d'Avitaya

Influence of liquid surface tension on stiction of SOI MEMS

Stiction during the release step is one of the most important problems in micro-electromechanical systems (MEMS). This phenomenon, due to capillary forces and molecular adhesion, appears during drying after wet etching. This force is directly proportional to the surface tension of the last liquid used before drying. In this paper, we present firstly an experimental study of the influence of the liquid surface tension on the stiction of the SOI microstructure. In a second part we show how a new industrial bath process is able to perform the complete release step (etching, rinsing and drying).

Light Emission at Room Temperature from Si/CaF2 Multilayers

We have synthesized, by Molecular Beam Epitaxy (MBE), Si/CaF2 multilayers which are optically active at room temperature. The photoluminescence spectra present a blue shift for decreasing Si layer thickness, in analogy to those obtained from porous silicon when the porosity is increased. We find a critical dependence of the photoluminescence efficiency on the thickness of the Si layers. We compare the experimental results to ab initio calculations of the band structure of Si/CaF2 multilayers which predict the band gap opening and the presence of confined and interface states leading to a quasi-direct band gap.

Step-driven molecular adsorption of Sb on Si(111)

Abstract Adsorption of Sb on a misoriented Si(111) surface is investigated by thermodesorption Auger spectroscopy. The spectra reveal that, in the submonolayer range, new adsorption states appear for the vicinal surface which do not exist for the nominal one. Quenched molecular-dynamics simulations, in which Si and Sb are modeled by many-body tight-binding potentials, allow us to interpret these new states as due to a molecular adsorption at the steps instead of a dissociative one on the terraces.

Isobar, low energy electron diffraction and loss spectroscopy measurements of cesium covered (110) gallium arsenide

Abstract Two thermodynamic “surface phases” are observed in the first Cs monolayer on (110) GaAs. These phases are characterized by different physical properties. We have also shown that in the first step of cesiation, the Cs atom is chemically bonded to the Ga atoms.

Trapping levels in (nc-Si/CaF2)n multi-quantum wells

Abstract Trapping levels which govern the vertical transport in (nc-Si/CaF2)n multi-quantum wells were investigated using two different techniques: (a) the temperature dependence of the dark current and (b) the thermally stimulated depolarization current technique (TSDC). Measurements by the first technique showed that the conduction mechanism was thermally activated above 200 K with activation energies of 0.35–0.7 eV. These activation energies were found to increase with increasing electric field. TSDC measurements showed also the existence of at least one broad peak above 200 K with estimated activation energies in the range of 0.4–0.45 eV. Analysis of the peak by the fractional heating method showed a continuous distribution of defect states from 0.3 to 0.83 eV.

LEED, AES and work function measurements on clean and cesium covered polar faces of GaP

Abstract After argon bombardment and annealing both the (111) and (111) faces of GaP show a (1 × 1) LEED pattern. The stabilization of the polar termination is probably obtained by charging of surface states. Measurements of the work function, the Auger spectrum and the LEED pattern during cesium deposition at room temperature suggest disordered cesium adsorption limited to a monolayer.

Optical absorption evidence of quantum confinement in Si/CaF2 multilayers grown by molecular beam epitaxy

Abstract We have investigated the physical properties of nanocrystalline Si/CaF 2 multilayers grown by molecular beam epitaxy, which exhibit efficient visible luminescence at room temperature. X-ray diffraction under grazing incidence as well as transmission electron microscopy demonstrate the periodicity of the multilayers. Extended X-ray absorption fine structure measurements show that the dimensions of the Si grains within the Si layers do not exceed 1.5 nm. We report on the optical absorption coefficient deduced from transmission measurements performed on samples deposited on CaF 2 substrates. The resulting optical pseudogap presents a large blue shift for decreasing Si layer thickness. The latter results are consistent with quantum confinement of carriers in the low-dimensional Si structures.

Charge carrier transport in Si/CaF2 heterostructures controlled by forming bias

Electrical properties of structures consisting of CaF 2 and Si nanosize layers have been investigated. There is a strong asymmetry between forward and reverse current curves, as well as a shift of the voltage at which the current is null. It has been found that after some electrical forming of the structures the current exhibits a well resolved non-monotonous N-type behavior at reverse bias conditions. The corresponding region of negative differential resistance appears only once a forward bias has been applied. An attempt is made to interpret the observed effect in terms of capturing of the carriers within the structure and their subsequent release through the structure via tunneling.

Silicon homoepitaxy on high index surfaces and the effect of antimony on this growth

Abstract We report on the structure of Si films grown by molecular beam epitaxy on highly misoriented Si(111) surfaces and on the influence of Sb on this growth. Although the equilibrium morphology of these surfaces is a mixture of single and triple height steps, one observes for temperatures lower than the 1 × 1 to 7 × 7 transition one, by LEED, AFM and HRTEM, that the MBE growth gives rise to an important roughness. On the contrary, at higher temperature or when Si and Sb are coevaporated, we stabilize a regular array of steps. We show that these steps are triatomic in the former case and monoatomic in the latter. Such a behaviour illustrates the major role played by the 7 × 7 reconstruction on the growth morphology of Si films.

Thermodesorption mass spectrometry study of the adsorption of Sb on misoriented Si(111)

Abstract Adsorption of Sb on a misoriented Si(111) surface is investigated by thermodesorption mass spectrometry (TD-MS). The spectra confirm the existence, in the submonolayer range, of new adsorption sites induced by the presence of steps, previously shown by Auger spectroscopy thermodesorption (TD-AES) and tentatively attributed, through simulations, to molecular adsorption at the steps rather than dissociative on the terraces. The present TD-MS measurements completely confirm this interpretation, and also give new information on the nature of the species leaving the surface (essentially Sb2) and on their emission laws (orientational desorption).