Antonio Munoz-Yague

Optimum design of thyristor gate—Emitter geometry

This paper describes a new method of studying the influence of the gate-emitter geometrical configuration of thyristors upon their triggering performances. This method allows, for devices of any geometrical complexity, to calculate the emitter bias voltage distribution prior to turn-on and hence to compare the behavior of these devices from a geometrical point of view. The results may be used as guide lines for the optimum design of gate-emitter configurations. As examples, precise design rules are given for standard thyristors and application to amplifying interdigited gate thyristors are outlined.

A GaAlAs-GaAs integrated coherence modulator

This paper presents a novel integrated III-V semiconductor waveguide modulator specially designed to generate optical delays of several hundred micrometers. This is achieved by simultaneous propagation of transverse electric (TE) and transverse magnetic (TM) lowest order modes in an original layered waveguide exhibiting a group birefringence greater than 0.02 at 1.3 /spl mu/m. The device has 40% contrast, a switching voltage of 7 V with a 10-mm long electrode and is suitable for transmission and multiplexing of signals by coherence modulation of light in an optical fiber network powered by a short coherence source such as a superluminescent diode.

Highly birefringent and monomode GaAlAs-GaAs planar optical waveguide

A novel optical waveguide exhibiting a layered core region is proposed. Owing to the original design of the core stack and form birefringence in the multilayer, a waveguide supporting both TE and TM lowest-order modes with high confinement has been obtained. It has been designed, fabricated, and characterized and presents a modal birefringence greater than 0.01, which is in good agreement with the calculated values.

Generalization of Bragg reflector geometry: Application to (Ga,Al)As‐(Ca,Sr)F2 reflectors

Bragg reflectors based on (Ca,Sr)F2 and (Ga,Al)As are studied. Modeling and fabrication of these structures by molecular‐beam epitaxy were performed. Quarter‐wave Bragg reflectors were found to present an excellent reflectance around the wavelength of interest, 870 nm, for only three periods of bilayers. However, the structures grown exhibited cracks after epitaxy due to thermal stress between both materials. To alleviate this problem, other reflector geometries were investigated consisting of deviations from the classical Bragg reflector. The new geometries enable one to reduce the absolute or relative fluoride thickness within the structure. The results obtained show that the use of adequate geometries allows one to overcome the stress problem, and good heteroepitaxial reflectors with a crack‐free surface morphology were obtained.

Integrated optical detection subsystem for functional genomic analysis biosensor

We present an optical microsystem aimed to be integrated into a nanomechanical biosensor for functional genomic analysis. The operation principle is based on a sub-nanometer resolution optical measurement of a cantilever deflection caused by a surface stress when the target nucleic acid sample hybridises to the nucleic acid probe on the active side of the cantilever. The resulting deflection, of the order of nanometers, is measured by an optical system, in which a laser beam reflects off the back of the cantilever to a position sensitive photo-detector. We report in this paper on the design, fabrication and test of the optical head associated with an optical coupling system which enables detection of the presence of target nucleic acid on the cantilever by amplifying the deflection caused by the stress.

Status Of Fluoride-Semiconductor Heteroepitaxial Growth

Molecular beam epitaxy of structures associating alkaline-earth fluorides and semiconductors has received considerable attention in the last few years. In this paper, we review the results published paying special attention to structures associating Ca, Sr, Ba fluorides and Si, GaAs, InP semiconductors. General trends for fluoride/semiconductor growth behavior are emphasized, as well as the problems encountered in the growth of semiconductor/fluoride heterostructures.

On a Semianalytic Method for Solving Laplace's Equation

The advantages of semianalytic methods for solving Laplaces equation, compared to classical methods, have been pointed out recently. An approach of the former type is proposed here for twodimensional problems. The potential (or other physical quantities depending on the particular problem) is obtained in the form of a finite series: each term of this series corresponds physically to the potential created by a straight line with a uniform charge density. Basically the method consists of considering the required potential distribution to be created by an arrangement of such charged lines. The charge density of each line is then calculated in order to satisfy exactly the boundary conditions at a number of points equal to the number of line sources. the precision of the method depends on the number of sources and their arrangement;it can be very satisfactory with a relatively low number of sources especially in problems involving curve-shaped boundaries or some circular symmetry.

Integrated optical coupling element for functional genomic analysis biosensor

We present here a design of a coupling element aimed to be integrated into a nanomechanical biosensor for functional genomic analysis. The operation principle is based on a sub-nanometer resolution optical measurement of a cantilever deflection caused by a surface stress when the target nucleic acid sample hybridizes to the nucleic acid probe on the active side of the cantilever. The resulting deflection, of the order of nanometers, is measured by an optical system, in which a laser beam reflects off the back of the cantilever to a position sensitive photo-detector. We study in this paper three polymer optical coupling systems which could allow to detect the presence of target nucleic acid on the cantilever by amplifying the deflection caused by the stress.

Dual-purpose single-cavity oxide-confined VCSEL photodetector

The increasing interest for high-speed, compact and low cost devices for optoelectronic applications such as bi-directional optical interconnects, optical imaging or telemetry has recently led to focus on the ability for the vertical-cavity surface-emitting lasers to be used as resonant cavity enhanced photodetectors for dual-purpose applications. Here we present results on design, fabrication and characterization of an oxide-confined 830nm top-emitting laser for self-aligned emission and photodetection. In this single-cavity GaAs-based device, submitted alternatively to forward and reverse bias, the oxide layer is not only used to obtain a single mode emission but also to enable decoupling between a small surface emission and a large surface detection. However the optical path is observed to change because of the refractive index difference between the oxidized and non-oxidized zones of the structure. This leads to a detrimental blue-shift on the wavelength of the Fabry-Perot cavity mode. In this work, we demonstrate this effect in photodetection by the means of spatially localized photocurrent and reflectance spectra measurements. These results show that the photocurrent is correctly collected in the whole device despite of the presence of an oxide layer. The results obtained on selective etching for optimisation of this dual-purpose device are presented.

Generalization of Bragg reflector geometry: application to (Ga,Al)As - (Ca,Sr)F2 reflectors

Bragg reflectors of three geometrical configurations are considered analytically and experimentally to solve the problem of cracking which develops due to thermal stress between the two materials used. The Bragg reflectors are based on (Ca,Sr)F2 and (Ga,Al)As and are grown by means of molecular beam epitaxy. Three geometrical solutions are considered: (1) three material combinations within quarter-wave structures; (2) mixed reflectors of GaAs-(Ca,Sr)F2 and GaAs-AlAs in shifted Bragg reflectors with reduced layer thicknesses; or (3) generalized Bragg structures based on asymmetrical geometries. The absolute or relative fluoride thicknesses in the structures can be reduced by means of the proposed configurations. Effective heteroepitaxial reflectors are set forth that have crack-free surface morphologies because the structures of the generalized Bragg reflectors reduce the stress inherent in the devices.