The design of bottom mirrors for resonant cavity enhanced (RCE) GaAs homojunction far-infrared (FIR) detectors has been investigated in the framework of three possible projects. The results show that neither the bottom contact layer of the detector itself nor the distributed Bragg reflector, which has been widely employed in near- and mid-infrared detectors, can perform well as bottom mirrors for FIR detectors. A new kind of bottom mirrors based on undoped/doped GaAs layers is proposed and optimized. Though the absorption cannot be neglected, the bottom mirror shows a satisfactory effect. The resulting absorption probability (as well as the quantum efficiency) in the detector cavity for this kind of RCE p-GaAs FIR detector is three times of the normal p-GaAs homojunction FIR detector demonstrated experimentally. This kind of bottom mirror design opens a new way to increase the quantum efficiency in homojunction FIR detectors.

When silicon thin films are deposited by plasma enhanced chemical vapor deposition in a plasma regime close to powder formation, a new type of material, consisting of an amorphous matrix in which silicon nanocrystallites are embedded is obtained. This material, named hydrogenated polymorphous silicon (pm-Si:H), exhibits enhanced transport properties with respect to state-of-the-art hydrogenated amorphous silicon (a-Si:H). In order to understand the origin of such improved properties, we investigated structural characterization of pm-Si:H films. High resolution transmission electron microscopy (HRTEM) micrograph, micro-Raman and infrared spectra of the films are presented. The crystallite sizes deduced from the Raman spectra are supported by the HRTEM measurements. The infrared stretching modes of pm-Si:H films present a band at ~2030 cm−1 attributed to hydrogen platelets. Two approaches are then given in order to explain the enhanced photoconductivity properties. The first one, qualitative, appeals to low density of states at the Fermi level $N(E_{\rm F})$ and low capture cross-section of electrons $\sigma_{\rm c}$ due to the improved amorphous matrix. The second, more quantitative, suggests that recombination mainly occur at dangling bonds at the surface of the crystallites. Considering the dangling bond density at silicon surface passivated by hydrogen and the description of multiphonon carrier capture, both given in the literature, we derive $N(E_{\rm F})$ and $\sigma_{\rm c}$ values in good agreement with experiments.

A numerical study of a nitrogen cold plasma created by a pulsed discharge in a point-to-plane geometry at 4 torr is presented. The relative model is based on fluid description of the cold plasma, on Poisson's equation for the electric field and on balance equations for the excited population concerning only some vibrational band of molecular nitrogen (C3∏u, B3∏g and A$^3\sum_{\rm u}^+$). Secondary ionization phenomena and longitudinal diffusion effects are included in the model and their contribution to the glow-discharge establishment is studied. Results for space and time variations of the charged particles, electric field, potential and electronic current densities are reported. Particular attention was paid to the physical factors forming the cathodic layer and influencing its evolution. Results concerning the influence of the electronic current density on the creation of excited (radiative and metastables) particles are presented. According to these results, the plasma of the glow discharge occurs by means of three successive sequences with different characteristics. During the first sequence the gap is slowly filled of ions formed close to the anode, then in the second one an ionizing front formed close to the anode is propagating towards the cathode with an average velocity of 2 × 106 cm/s. It forms the cathodic layer zone and starts the participation of the secondary ionization effects leading to the third sequence which deals with the glow discharge establishment. The first significant production of excited states occurs within the ionizing front but the most important one is obtained when the glow discharge is established. It has been shown that at 4 torr and a gap of 1 cm, a mean electronic current density of 5 mA/cm2 is sufficient to create 109 cm−3 of (B3∏g, v = 0), 108 cm−3 of (C3∏u, v = 0) and 1011 cm−3 of (A$^3\sum_{\rm u}^+$, v = 0 ) excited particles.

A known electrodynamic approach is generalized to guided-wave structures using a hypothetical space-dispersive medium with drifting charge carriers and simultaneously possessing elastic, piezoelectric, and magnetic properties. On the basis of Maxwell's equations along with the appropriate equations of medium motion, the power-energy theorem is derived in the general form involving additional contributions from specific properties of the medium. The general power-energy relation yields particular expressions obtained previously for specific cases of the elastic piezo-dielectrics, magnetized ferrites, and drifting charge carriers in nondegenerate plasmas. Substantial features of our electrodynamic study are the allowance for medium losses and the separation of potential fields peculiar to the slow quasi-static waves which propagate in such active media independently of the fast electromagnetic waves of curl nature. Separating the potential fields gives a certain modification of electromagnetic terms in the power-energy theorem.

A vectorial formalism for analysis and design of polyphase synchronous machines without reluctance and saturation effects is described. We prove the equivalence of such a machine with a set of magnetically independent machines, which are electrically and mechanically coupled. Specific problems of polyphase machines can thus be favorably analyzed with this concept. Rules of conception and constraints on electric supply can be deduced. Moreover the vectorial approach, which generalizes the complex phasor method, can also be used to control n-leg voltage source inverters. This methodology is applied to 3-phase and 6-phase synchronous machines.

Transmission Line Transformers (TLT) based on the use of ferrite beads are presented. This work aims at optimising the performance of the voltage gain and the compactness of the TLT according to the position, the type and the number of ferrites used. The ferrites have been selected taking into account two main parameters: the maximum currents flowing through the outer conductor of the lines of a TLT without ferrite beads and the current frequencies. The function of these ferrites is to decrease the effect of parasitic short-circuit transmission lines between the outer conductors of the coaxial cables of the TLT. Voltages and secondary currents are measured on each cable. The voltage gain achieved reaches the optimum theoretical value thanks to the use of ferrites for a 2, 4 and 10-stage transmission line transformer. Each cable is shorter than 1.5 meter in length which provides an unquestionable advantage of compactness.

An insertable electron beam ionizer into a quadrupole-based secondary ion mass spectrometer instrument has been designed and installed to analyze sputtered neutrals. The optimum design conditions of the ionizer have been obtained by modeling various configurations of the system using a simulation program developed by us. The program has allowed us to compute the potentials and ion trajectories inside the system to test the performance of the ion optics design. We have investigated the advantages of using a large ionization volume with low electron current to minimize the space charge effect in the ionizer, as this is the major problem in this type of instrument. In addition, we have used the simulations to obtain all electrodes voltages which provide an efficient suppression of residual gas and secondary ions. A good useful yield was obtained, even with low electron densities, thanks to the high geometrical acceptance of the ionizer and its large active volume. This configuration implies less thermal radiation in the ionizer and, in addition, a longer life time of the filament. Although the signal of residual gas not suppressed (i.e. in residual gas mode) is two orders of magnitude higher than the signal of sputtered neutrals, we have achieved a good background suppression.