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Abstract

The thermal oxidation of an Al-rich AlGaAs buried layer is a common established technique used to improve the performances of some optoelectronic devices, like VCSEL or optical waveguides, in terms of electro-optical confinement. This oxidation technique is usually proceeding laterally, which allows achieving good results but leads to some difficulties on the control of the shape and size of the oxidized areas. In this work, a new technology to oxidize GaAs/AlAs epitaxial structures which avoids these limitations is presented. This method consists of an oxidation through the top of the sample, allowing in consequence a total control of the shape of oxidation by means of photolithography. For this purpose the method has two steps: first, the intentional creation of defects in the top GaAs layer, in order to make it possible the oxidant species diffusion through this material, and second the planar oxidation of the AlAs layer. In this paper this technique is thoroughly studied: different methods to create defects in the GaAs layer have been analysed, and the optimization of the procedure has been achieved leading to a uniform oxidation and a reduced lateral oxidation spreading. Finally a comparison between the experiments and simulations has been realized in order to provide an explanation for this type of vertical oxidation. This innovating technique allows addressing separately the electrical and optical operating aspects of optoelectronic devices, thus opens to novel structures with controlled transverse optical behaviour.

Mots-Clés / Keywords

Abstract

A new imaging method is presented enabling the monitoring of the lateral wet thermal oxidation of a thin Al-containing layer embedded in a vertical cavity lasers (VCSEL) structure. This method is based on the measurement of the modification of the VCSEL reflectivity spectrum inherent to the aperture layer refractive index change, with an observation window restricted to the wavelength ranges for which this reflectivity variation is maximal. The main purpose is the accurate control of the buried confinement aperture, and, thereby, that of the electro-optical characteristics of the laser device. The kinetics of the lateral oxidation has been studied for small-size aperture VCSEL (310 µm) and for long-range oxidation depths. This straightforward method based on an optical imaging system will enable robust improvement of the production yield of this multifactor-dependent technological process.

Abstract

The thermal oxidation of an Al-rich AlGaAs buried layer is a common established technique used to improve the performances of some optoelectronic devices, like VCSEL or optical waveguides, in terms of electro-optical confinement. This oxidation technique is usually proceeding laterally, which allows achieving good results but leads to some difficulties on the control of the shape and size of the oxidized areas. In this work, a new technology to oxidize GaAs/AlAs epitaxial structures which avoids these limitations is presented. This method consists of an oxidation through the top of the sample, allowing in consequence a total control of the shape of oxidation by means of photolithography. For this purpose the method has two steps: first, the intentional creation of defects in the top GaAs layer, in order to make it possible the oxidant species diffusion through this material, and second the planar oxidation of the AlAs layer. In this paper this technique is thoroughly studied: different methods to create defects in the GaAs layer have been analysed, and the optimization of the procedure has been achieved leading to a uniform oxidation and a reduced lateral oxidation spreading. Finally a comparison between the experiments and simulations has been realized in order to provide an explanation for this type of vertical oxidation. This innovating technique allows addressing separately the electrical and optical operating aspects of optoelectronic devices, thus opens to novel structures with controlled transverse optical behaviour.

Mots-Clés / Keywords

Résumé

Nous étudions l'amélioration des propriétés électriques des VCSELs (Vertical Cavity Surface Emitting Laser) de grande dimension (100um) à injection metallique annulaire pour application à la génération de puissance et pour la manipulation de solitons de cavité. Une simulation électrique nous a permis de quantifier l'amélioration de l'uniformité d'injection des porteurs apportée par les solutions technologiques que nous proposons de réaliser: l'adjonction d'une couche conductrice d'ITO à la surface du miroir supérieur du laser est ici évaluée.

Résumé

Nous présentons une technique de réalisation d'un oxyde enterré localisé. Il s'agit d'un procédé, appliqué en surface, basé sur la photolithographie, la gravure sèche par plasma et l'oxydation thermique humide. Cette méthode permet d'oxyder localement une couche enterrée riche en Aluminium per un processus vertical. Contrairement à l'oxydation latérale habituelle elle permet la réalisation de différentes formes des zones oxidées et ouvre l'accès à des dimensions de diaphragmes d'oxyde plus petites et mieux controlées.