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Abstract

A thorough study of wet thermal oxidation in AlAs/AlxGa1-xAs superlattices is presented. The results shown here demonstrate that the final oxidation depth can be finely tuned via the composition and thickness of AlxGa1-xAs into the digital alloy. A complete model of oxidation in these structures is proposed, relying on diffusion through the AlAs layer, its oxidation and an additional effect due to the AlxGa1-xAs intermediate barriers. This barrier contribution is shown to further improve the control of the oxidation rate, and thereby fabrication of sophisticated AlOx/GaAs integrated optoelectronic devices.

Abstract

Preparation of processed GaAs surface cleaning in view of molecular beam epitaxy regrowth by means of a O2SF6 microwave plasma has been investigated. Photoemission, Auger electron spectroscopy, atomic force microscopy and secondary ion mass spectrometry have been used for characterization. The O2SF6 plasma treatment was found to be very efficient for decontaminating the GaAs surface and leads to the formation of an oxide layer that can be taken off by a thermal or low temperature H-plasma assisted deoxidation. The levels of oxygen and carbon contaminants at the regrowth interface were measured to be in the range of a standard homoepitaxial layer-epiready substrate interface. Fluorine was observed to be eliminated upon deoxidation while sulphur is present, particularly in the case of low temperature grown layers. This plasma treatment was found to be efficient for preparation of processed GaAs surfaces for molecular beam epitaxial regrowth.

Abstract

A thorough study of the selective wet oxidation in digital AlxGa1xAs alloys is presented. We report experimental results and physical interpretation on the oxidation kinetics within those ranges of the AlGaAs composition (x = 0.95 to 1) and layer thickness (20 to 50 nm) of interest for oxide-aperture vertical-cavity surface-emitting laser (VCSEL) application. We demonstrate the high controllability of the oxidation reaction between different Al compositions; made different thanks to the use of digital alloys. Unlike standard alloys, we measured an invariability of the oxidation rates in the studied thickness range (2050 nm), implying a better control of the fabrication process. The dependence of the reaction rate with the temperature is expressed as an Arrhenius law. Two activation energies (1.2 and 0.55 eV) have been derived for composition ranges of x = 0.950.98 and x = 0.991, respectively, revealing that two different mechanisms are involved depending on the Al content and the superlattice structure of the digitally-grown AlGaAs.

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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.

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We report an experimental study of GaAs etching by ICP-RIE based on Cl2:N2 chemistry. The influence of the RF source power, the chlorine dilution, the RF platen power, and the process pressure at several substrate temperatures are investigated. An optimized process is proposed to get routinely GaAs nanowires of 1 ¼m high and about 30 nm in diameter with a full top-down approach combining electron beam lithography and Ni lift-off steps.

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We present a comprehensive study of spectral photoluminescence (PL), photoconductivity and Hall mobility in undoped, n and p-type modulation-doped quantum wells of Ga1x InxNyAs1y/GaAs with varying nitrogen concentration.We show that the increasing nitrogen composition red shifts the energy gap and this red shift is accompanied with a reduction of the 2D electron mobility in the quantum wells. True temperature dependence of the band gap, free from errors associated with nitrogen induced exciton trapping effects, is observed because in the modulation doped QWsamples PL emission is dominated by bandto- band recombination and the S-shape temperature dependence is eliminated. Excellent fit to semi-experimental Varshni equation is obtained and the temperature dependence of the band gap in the linear regime (dE/dT) is tabulated as a function of nitrogen concentration and the type of dopant.

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