Hydrogen and nitrogen release processes in amorphous silicon nitride dielectrics have been studied by MeV ion scattering spectrometry in combination with infrared spectroscopy. The outdiffusion of those light constituents was activated by the thermal energy supplied to the samples by rapid thermal annealing treatments. Molecular models of how these reactions proceed have been proposed based on the information obtained from the infrared spectra, and the validity of the models has been tested by an analysis of the activation energy of the desorption processes. For this purpose, the evolution of the hydrogen concentration versus the annealing temperature was fitted to an Arrhenius-type law obtained from a second-order kinetics formulation of the reactions that are described by the proposed structural models. It was found that the low values of the activation energies can be consistently explained by the formation of hydrogen bonding interactions between Si-H or N-H groups and nearby doubly occupied nitrogen orbitals. This electrostatic interaction debilitates the Si-H or N-H bond and favors the release of hydrogen. The detailed mechanism of this process and the temperature range in which it takes place depend on the amount and the proportion of hydrogen in Si-H and N-H bonds. Samples with higher nitrogen content, in which all bonded hydrogen is in the form of N-H bonds, are more stable upon annealing than samples in which both Si-H and N-H bonds are detected. In those nitrogen-rich films only a loss of hydrogen is detected at the highest annealing temperatures.

We have analyzed the structural and optical properties of Si implanted with very high Ti doses and subsequently pulsed-laser melted (PLM). After PLM, all samples exhibit an abrupt and roughly uniform, box-shaped Ti profile, with a concentration around 2 Â 10 20 cm À3, which is well above the Mott limit, within a 150 nm thick layer. Samples PLM-annealed at the highest energy density (1.8 J/cm 2 ) exhibit good lattice reconstruction. Independent of the annealing energy density, in all of the samples we observe strong sub-bandgap absorption, with absorption coefficient values between 4 Â 10 3 and 10 4 cm À1. These results are explained in terms of the formation of an intermediate band (IB) originated from the Ti deep levels.

We report room-temperature operation of 1 × 1 cm2 infrared photoconductive photodetectors based on silicon supersaturated with titanium. We have fabricated these Si-based infrared photodetectors devices by means of ion implantation followed by a pulsed laser melting process. A high sub-band gap responsivity of 34 mV W−1 has been obtained operating at the useful telecommunication applications wavelength of 1.55 μm (0.8 eV). The sub-band gap responsivity shows a cut-off frequency as high as 1.9 kHz. These Si-based devices exhibit a non-previous reported specific detectivity of 1.7 × 104 cm Hz1/2 W−1 at 660 Hz, under a 1.55 μm wavelength light. This work shows the potential of Ti supersaturated Si as a fully CMOS-compatible material for the infrared photodetection technology.

We have analyzed the spectral sub-bandgap photoresponse of silicon (Si) samples implanted with vanadium (V) at different doses and subsequently processed by pulsed-laser melting. Samples with V concentration clearly above the insulator-metal transition limit show an important increase of the photoresponse with respect to a Si reference sample. Their photoresponse extends into the far infrared region and presents a sharp photoconductivity edge that moves towards lower photon energies as the temperature decreases. The increase of the value of the photoresponse is contrary to the classic understanding of recombination centers action and supports the predictions of the insulator-metal transition theory.

Heterojunction solar cells based on molybdenum sub-oxide (MoOx) deposited on n-type crystalline silicon have been fabricated. The hole selective character of MoOx is explained by its high workfunction, which causes a strong band bending in the Si substrate. This bending pushes the surface into inversion. In addition, the substoichiometry of the evaporated MoOx layers leads to a high density of states within the bandgap. This is crucial for charge transport. The J-V electrical characteristics at several temperatures were analysed to elucidate the dominant charge transport mechanisms of this heterojunction structure. We have identified two different transport mechanisms. At low bias voltage, transport is dominated by hole tunneling through the MoOx gap states. At higher voltage the behavior is similar to a Schottky junction with a high barrier value, due to the high MoOx work function. These results provide a better understanding of the hole selective

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We have analyzed the increase of the sheet conductance (ΔG□) under spectral illumination in high dose Ti implanted Si samples subsequently processed by pulsed-laser melting. Samples with Ti concentration clearly above the insulator-metal transition limit show a remarkably high ΔG□, even higher than that measured in a silicon reference sample. This increase in the ΔG□ magnitude is contrary to the classic understanding of recombination centers action and supports the lifetime recovery predicted for concentrations of deep levels above the insulator-metal transition.

The effect of rapid thermal annealing processes on the properties of SiO 2.0 and SiN 1.55 films was studied. The films were deposited at room temperature from N 2 and SiH 4 gas mixtures, and N 2 , O 2 , and SiH 4 gas mixtures, respectively, using the electron cyclotron resonance technique. The films were characterized by Fourier transform infrared spectroscopy ͑FTIR͒ and electron paramagnetic resonance spectroscopy. According to the FTIR characterization, the SiO 2.0 films show continuous stress relaxation for annealing temperatures between 600 and 1000°C. The properties of the films annealed at 900-1000°C are comparable to those of thermally grown ones. The density of defects shows a minimum value for annealing temperatures around 300-400°C, which is tentatively attributed to the passivation of the well-known EЈ center Si dangling bonds due to the formation of Si-H bonds. A very low density of defects (5ϫ10 16 cm Ϫ3 ) is observed over the whole annealing temperature range. For the SiN 1.55 films, the highest structural order is achieved for annealing temperatures of 900°C. For higher temperatures, there is a significant release of H from N-H bonds without any subsequent Si-N bond healing, which results in degradation of the structural properties of the film. A minimum in the density of defects is observed for annealing temperatures of 600°C. The behavior of the density of defects is governed by the presence of non-bonded H and Si-H bonds below the IR detection limit.