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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

The effects of thermal annealing on optically transparent electrodes of ITO (indium tin oxide) contact deposited on p-type Be-doped GaAs have been investigated by means of the transfer length method and secondary ion mass spectroscopy measurements. This study shows that the temperature that minimizes the specific contact resistance of ITO/GaAs (500 °C) greatly differs from the temperature that leads to a maximum conductivity of the ITO layer (600 °C) and from the values reported on ITO/GaAs in the literature. The oxygen diffusion in the semiconductor layer and its interaction with the beryllium dopant is pointed out to explain these differences.

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.

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.

Abstract

We present the results of hot-electron momentum relaxation studies for longitudinal transport in modulation doped GaxIn1xNyAs1y/GaAs quantum wells. Experimental results show that the high field drift velocity saturates at a value close to 1×107 cm/s with no evidence for negative differential resistance or instabilities. Experimental results are compared with a simple theoretical model for transport taking into account the effect of nonequilibrium phonon production. Model calculations indicate that enhanced momentum scattering for electrons with nondrifting hot phonons may be the cause for the reduction in drift velocity.