InGaAsP/InP micro-waveguides are fabricated by a deep (>3 mum) Reactive Ion Etching. The devices losses are measured by the Fabry-Perot technique for guide width contained between 10 mum and 0.5 mum. The measured losses range from 2 dB/mm to 14 dB/mm. (C) 2004 Wiley Periodicals, Inc.

Background The revelation of an acceptable rate of users still treated one year after initiation of a substitution program with high-dose buprenorphine (HDB) has contributed in the validation of the interest of the molecule in this indication. However the frequency of early drop-outs (after the first consultation), when treatment is set-up, is frequently evoked, although undocumented, by general practitioners.Objective During analysis of a survey on the follow-up of opiate addicts starting substitution therapy with HDB, we attempted to assess the frequency of early drop-outs and identify the contributing factors.Method Among the 1085 patients included in the study and in whom induction therapy had been prescribed, 656 were assessed after 12 months' follow-up.Results Age, precariousness, lack of social support and partial access to care (lack of health insurance, previous contact with the prescriber) were significantly associated with early drop-out. The consumption of psychoactive products and their administration mode, during the 30 days prior to the first consultation of those loss to follow-up, also differed from those of patients who remained within the care system.Conclusion Knowledge of the factors related to frequent early drop-out during induction of HDB substitution therapy, and bearing this in mind, would permit the organisation of more attentive management and hence reduce the drop-out rate.

The fabrication and characterisation of low-loss InGaAsP/InP optical submicron waveguides made with ICP etching is reported. Their width ranges from 0.2 to 2 /spl mu/m. For the 0.5 /spl mu/m width, the propagation losses at /spl lambda/=1.55 /spl mu/m as low as 4.2 dB/mm have been measured.

BACKGROUND:The revelation of an acceptable rate of users still treated one year after initiation of a substitution program with high-dose buprenorphine (HDB) has contributed in the validation of the interest of the molecule in this indication. However the frequency of early drop-outs (after the first consultation), when treatment is set-up, is frequently evoked, although undocumented, by general practitioners.OBJECTIVE:During analysis of a survey on the follow-up of opiate addicts starting substitution therapy with HDB, we attempted to assess the frequency of early drop-outs and identify the contributing factors.METHOD:Among the 1085 patients included in the study and in whom induction therapy had been prescribed, 656 were assessed after 12 months' follow-up.RESULTS:Age, precariousness, lack of social support and partial access to care (lack of health insurance, previous contact with the prescriber) were significantly associated with early drop-out. The consumption of psychoactive products and their administration mode, during the 30 days prior to the first consultation of those loss to follow-up, also differed from those of patients who remained within the care system.CONCLUSION:Knowledge of the factors related to frequent early drop-out during induction of HDB substitution therapy, and bearing this in mind, would permit the organisation of more attentive management and hence reduce the drop-out rate.

The purpose of this study was to analyze the impact of high-dose buprenorphine substitution therapy in opiate-dependent patients in terms of use of psychoactive substances, associated risks, social integration, and the social cost generated by the use of these substances. This was a longitudinal quantitative survey carried out in 1083 patients who were evaluated at three times: at the beginning of substitution therapy (D0), at 6 months and then at 12 months follow up (M6, M12). Data were collected with an anonymous self-administered questionnaire, completed in the presence of an investigating physician. Results demonstrated that patients treated with high-dose buprenorphine for 6 months, consumed fewer psychoactive drugs (heroin, cocaine, benzodiazepines) and had fewer associated risks. Additionally, several criteria involved in social integration showed improvement; morbidity and mortality decreased after the first 6 months of substitution therapy. These improvements were followed by a reduction in the social cost of drug use generated by the group of patients considered. These initial results require confirmation in the final analysis of the study taking into account the 12-month follow up.

Effects of SiNx deposition on undoped Ga0.47In0.53As bulk layer grown on InP substrate were investigated using Raman spectroscopy. No Raman shift as a result of strain induced from the dielectric deposition was observed in the Ga0.47In0.53As material, whatever the thickness and the temperature deposition used in the technological process. Some changes in the Raman spectra due to surface disorder effects were evidenced for the Ga0.47In0.53As samples passivated at 300 °C. These effects were confirmed by photocarrier-assisted experiments. Copyright © 1999 John Wiley & Sons, Ltd.

Effects of SiNx deposition on undoped Al0.48In0.52As and n+ Ga0.47In0.53As bulk layers grown on InP substrate have been investigated using Raman spectroscopy. No significant effects induced from the dielectric deposition have been observed in the Al0.48In0.52As material, whatever the thickness and the temperature deposition used in the technological process. On the contrary, slight modifications of the Raman spectra have been noticed for n+ Ga0.47In0.53As samples passivated at 300 °C. The observed differences have been interpreted as a surface potential decrease of 0.15 V and correlated to electrical measurements made on InP-based high electron mobility transistors. In this case, an increase of the maximum drain current has been observed in agreement with the surface potential change deduced from Raman experiments.

As a step further in the design of efficient organic semiconductors, we report here on the structural, spectroscopic and device characterization of octithiophene (8T), the linear conjugated octamer of thiophene. The X-ray structure and optical spectra under polarized light of the 8T single crystal are described for the first time. Vapor deposited 8T behaves as a p-type semiconductor whose transport properties are investigated in thin film transistors (TFTs). In particular, we show that the use of high purity 8T enhances by two orders of magnitude its field-effect mobility in TFTs to reach μFET = 1.8×10−2 cm2/V.s, a value similar to that of non-substituted sexithiophene (6T).

The efficiency of organic field‐effect transistors (OFETs) based on high‐purity α‐octithiophene (α‐8T) and its alkylated derivative DHα‐8T (see Figure) has been investigated, particular attention being paid to the influence of oligomer length, material purity, and film ordering on OFET performance, especially field effect mobility. The question of whether the mobility of the oligothiophenes keeps on increasing with chain length is discussed. magnified image

The purpose of this paper is to introduce UV sensors based on GaAs material and specially suited for low light power detection in spectroscopic systems and energy measurements of UV radiation in industrial and biomedical applications. Of particular interest here are n-type GaAs planar photoconductors optimized for UV detection and UV dosimeters made of plasma hydrogenated n+-type GaAs. After a description of the devices and their technology, an analysis of their electrical and optical properties is given. The results obtained are reviewed in terms of static responsivity and efficiency as a function of wavelength.

Raman scattering was used to probe electronic properties in In-based structures. First, Raman signatures of undoped and doped InAlAs and InGaAs bulk materials and Raman spectra of InAlAs-InGaAs heterostructures were recorded. Raman scattering by coupled longitudinal optic phonons and two-dimensional electron gas provides a powerful probe of electronic properties in this structure. More precisely, Raman results allowed information to be obtained on the two-dimensional gas electron carrier concentration. Then, a specific advantage of the micro-Raman method was demonstrated by the observation of the carrier concentration in the vicinity of the gate of an operating high electronic mobility transistor (HEMT). Qualitative variations of carrier concentration in the two-dimensional electron gas were observed and compared successfully with carrier concentration calculations using Monte Carlo simulations.

The purpose of this paper is to study the static response of photodetectors on a large range of incident power levels in order to point out saturation phenomena. After a description of the experimental set-up which has been used, obtained results on photoconductors and Metal-Semiconductor-Metal (MSM) photodiodes are presented and discussed in terms of linearity of their performances.

The purpose of this work is to use a picosecond laser to study the dynamic characteristics of photodetectors fabricated with III-V materials. Measurements have been carried out on an interdigitated InAlAs/InGaAs/InP Metal-Semiconductor-Metal (MSM) photodiode and an interdigitated InGaAs/InP photoconductor. A comparison between the impulse response of the photoconductor and the one of the MSM photodiode has been discussed in terms of cut-off frequencies of these two devices.

The purpose of this article is to compare the microwave performance of three photodetector types, an InGaAs/InP p-i-n photodiode, an interdigitated InAlAs/InGaAs/InP metal-semiconductor-metal (MSM) photodiode, and an interdigitated InGaAs/InP photoconductor (PC). Static and dynamic characterizations have been carried out at 1.3-mum wavelength using a directly modulated laser diode. Our experiments show that photoconductive detectors exhibit the best sensitivity for frequencies up to 3 GHz. (C) 1994 John Wiley & Sons, Inc.

Results concerned with the measurement of internal strain in pseudomorphic InxGa1-xAs/GaAs structures are reported, The Raman phonon wavenumbers of strain-relaxed alloy samples over a wide range of composition x are presented. Raman scattering experiments were carried out to measure the optical lattice modes of a series of InxGa1-xAs/GaAs strained-layer superlattices grown by molecular beam epitaxy on the (001) surface of GaAs substrates. The quantitative determination of strain in each type of strained layers was determined from the wavenumber shifts between commensurate and incommensurate layers.

Raman scattering has been used to probe the effects of both chemical and plasma etching on the photosensitive area of GaAs planar photoconductors, and also to examine the stress at a Si3N4 film/n-doped GaAs interface. Electrical performance on the photoconductors has been measured and then correlated to the Raman results. As expected, increasing the number of processes leads to slightly poorer electrical performance.

In this paper are given examples of III-V photodetector dynamic properties by using picosecond laser pulses. The impulse response characteristics are given and analyzed to improve the performance of the devices being studied.

Raman scattering has been used to characterize the effects of processing techniques on the photosensitive area of GaAs planar photoconductors. The longitudinal optic (LO) phonon observed in the first-order Raman spectra was studied to probe the consequences of both chemical and plasma etching on the crystalline quality of an n-doped GaAs photosentitive area. This method has also been used to examine the stress at the interface of a Si3N4 film and an n-doped GaAs surface. For this purpose, three specially designed GaAs planar photoconductors (SN 353, AN 344, SN 344) have been fabricated. Electrical measurements on the photoconductors support the results of Raman study. First, as expected, increasing the number of processes leads to slightly poorer electrical performance. Secondly, a significant strain-induced shift in the GaAs LO phonon frequency has been observed under the Si3N4 film for the AN 344 photoconductor. However, the electrical performances of this device clearly indicate no dramatic change in the value of the n-doped surface potential.

Planar photoconductors made with GaAs on silicon substrate have been studied with respect to static and dynamic responsivities as well as noise levels, in the 1 Hz-100 kHz frequency range. The results obtained have led to the determination of the specific detectivity which is in turn compared to those of GaAs planar photoconductors and Si photodiodes.<>