M. Ketata

Deep levels induced by low energy B+ implantation into Ge-preamorphised silicon in correlation with end of range formation

Abstract It is well established that low energy B+ ion implantation into Ge- (or Si) implantation pre-amorphised silicon allows ultra-shallow p+n junctions formation. However, this process is known to generate defects such as dislocation loops, vacancies and interstitials which can act as vehicles to different mechanisms inducing electrically active levels into the silicon bulk. The junctions studied have been obtained using 3 keV/ 10 15 cm −2 B + implantation into Ge-implantation pre-amorphised substrates and into a reference crystalline substrate. Accurate measurements using deep level transient spectroscopy (DLTS) and isothermal transient capacitance ΔC(t,T) were performed to characterise these levels. Such knowledge is crucial to improve the device characteristics. In order to sweep the silicon band gap, various experimental conditions were considered. The analysis of DLTS spectra have first showed three deep levels associated to secondary induced defects. Their concentration profiles were derived from isothermal transient capacitance at depths up to 3.5 μm into the silicon bulk and allowed us to detect a new deep level. The evolution of such defect distribution in correlation with the technological steps is discussed. The end of range (EOR) defect influence on electrical activity of secondary induced defects in ultra-shallow p+n diodes is clearly demonstrated.

Achieving of an optical very high frequency modulated wave source using heterodyne technique

We describe a method for generating an amplitude modulated optical wave in the range of the telecommunication frequencies. The originality is to guaranty a tunability of the source up to 275 GHz with about 45 MHz spectral width. The principle is based on the optical heterodyne of two DFB laser sources emitting around 1550 nm. After describing various existing methods for optical wave modulation and for millimetric signal generation, we concentrate our interest on the heterodyne technique. We carry out a study concerning the spectral width influence on the spectral purity of the generated signal. Then, the experimental measurement set-up is described, as well as characterization of the spectral width of the lasers. Finally, we present the results obtained in reception of the beat of two identical lasers on a 25 GHz bandwidth photodiode.

Influence of thermal aging on optical fiber properties

We investigate the effect of thermal aging on the optical properties of multimode silica fibers. Samples are submitted to several heating-cooling cycles of 8 h each. Analysis is performed using the optical spectrum analyzer, the fixed analyzer method, and the polarization-dependent loss measurements to determine respectively the signal loss values, the differential mode delay, and the polarization-dependent loss. Results show an increase of the attenuation coefficient, the differential mode delay, and the polarization-dependent loss values with the increase of aging time. The obtained results show a degradation of the optical properties of fibers from 1680 h related to structural changes, and to the increase of the optical anisotropy of fibers.

A model for diffusion of beryllium in InGaAs/InP heterostructures

Abstract This study reports on Be diffusion from a Be-doped (3×10 19 cm −3 ) In 0.53 Ga 0.47 As layer sandwiched between undoped InP layers grown by gas source molecular beam epitaxy. To explain the obtained experimental depth profiles, a kick-out model of substitutional interstitial diffusion mechanism, involving neutral Be interstitials for the InGaAs epilayer and singly positively charged Be interstitials for the InP epilayers, is proposed. Using the boundary conditions at the heterojunctions and taking into account the built-in electric field, Fermi level and bulk self-interstitial generation/annihilation effects, we obtained a good agreement between the simulated and experimental data.

Fiber-based Mach-Zehnder interferometric structures: principles and required characteristics for efficient modulation format conversion

Since new modulation schemes have become a great center of interest, Mach-Zehnder fiber fused interferometers (MZI) became necessary to ensure the direct detection (DD) from phase modulated signals, like DPSK (Differential Phase Shift Keying) or DQPSK. As these modulation schemes are very interesting in optical transmissions due to their capabilities, MZIs cannot be overlooked in the future optical links. In this paper, we review the base principles for using MZI as DPSK demodulators, and the major characteristics associated to these devices. In order to evaluate the minimal characteristics required for efficient modulation format conversion, we propose some numerical simulation results. Based on these results, we depicted a new fabrication process for the realization of MZIs by adiabatic stretching of one of the interferometers arm. This is carried out by a CO2 laser, and the fabrication major points that must be respected are discussed. After review the MZI thermal dependency mechanism, the last part presents the experimental results obtained for the quantification of MZI temperature control accuracy needed for its utilization as an 43 Gbit/s PSBT (Phase Shaped Binary Transmission) encoder.

Modeling of the transient enhanced diffusion of boron implanted into preamorphized silicon: the case of BF2+ implantation

We have simulated transient enhanced diffusion (TED) in the presence of end-of-range (EOR) defects produced by Ge amorphization followed by BF2 implantation. Ostwald ripening of EOR defects has been taken into account. A comparison of annealed profiles with equivalent B implantation shows that the existing models are not sufficient to simulate the BF2 experimental profiles where the boron diffusion depth is very low. We have proposed that the presence of fluorine can act as sinks for interstial boron and, hence, reduces the boron diffusion depth in order to obtain a good approximation of experimental profiles.

Be diffusion in InGaAs layers grown by gas source molecular beam epitaxy

The diffusion of Be from buried Be-doped InGaAs epitaxial layers, grown by gas source molecular beam epitaxy, has been studied for temperatures between 700 and 900°C. A kick-out model, involving neutral Be interstitial species and singly positively charged group III self-interstitials, is proposed for the diffusion mechanism.

Effect of thermal aging on Rayleigh backscattering in an optical fiber

We investigate the effect of thermal aging on the optical properties of multimode silica fibers. Samples were submitted to several heating-cooling cycles of 8 h each. Analyses were performed using an optical spectrum analyzer and an optical time-domain reflectometer to determine the signal loss. We proved that the attenuation coefficient is closely related to Rayleigh backscattering. Results show an increase of the attenuation coefficient with aging time. The obtained results show a degradation of the optical properties of fibers from 1680 h on, due to local variation of the refractive index induced by fluctuation of the material density.

Magnetic susceptibility of P+N junctions in correlation with the nature of silicon substrate: crystalline or pre-amorphised

Abstract Ge pre-amorphisation step is used to reduce the high diffusivity and the transient-enhanced diffusion of boron implanted in silicon. The aim of the process is to obtain shallow P + N junctions. The pre-amorphisation step was performed under different conditions (in ambient temperature and in nitrogen). Following the rapid thermal annealing step, end of range (EOR) defects appear at the amorphous–crystalline interface. These defects could influence the electrical characteristics of the P + N junctions. An experimental study concerning three samples has been performed without and under a magnetic field of 800 G. The magnetic susceptibility was essentially observed in the case of the reverse current. The impact of the magnetic field, studied by varying the sample temperature, permits us to show an increase of the magnetic susceptibility when the defects present in such structures are electrically active. These results are discussed in comparison with their deep-level transient spectroscopy (DLTS) spectra.

CO2-laser-beam-based technique for producing optical fiber components

A simple and handy technique to produce optical fiber components such as Bragg gratings has been used. A CO2 laser beam, focused on a single mode fiber, can change its optical properties locally, allowing therefore the creation of a Bragg grating inside the fiber itself. In the present study we investigate the effect of this laser beam on the fiber and show how optical fiber components can be produced. When exposing a single-mode optical fiber to a high-power CO2 laser beam a small device is developed insdie this fiber. Inside this micro-structure, the optical power is exchanged between the core and the cladding modes. This device may exhibit either a very selective rejection behavior similar to Bragg grating or an oscillating behavior like tapered fiber. The coupled mode theory combined with a mathmatical algorithm can be used to study the propagation of the modes involved in the fiber.