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 (3-10 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.

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.

A thorough study of the selective wet oxidation in digital AlxGa1–xAs 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 (20–50 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 = 0.95–0.98 and x = 0.99–1, respectively, revealing that two different mechanisms are involved depending on the Al content and the superlattice structure of the digitally-grown AlGaAs.