The crystallographic anisotropy of the lateral selective thermal oxidation of AlGaAs alloys is experimentally studied. The anisotropic behavior of this oxidation process, used primarily for building a lateral confinement in vertical surface emitting lasers (VCSEL), is quantified by varying different process parameters and the geometrical shapes of laterally oxidized mesa structures. This experimental study aims to have a better control of the oxide aperture shape used in oxide-confined photonics devices.

In this letter, we report the first experimental demonstration of microdisk resonators that are vertically coupled to their buried access waveguides on III-V semiconductor epitaxial structures using an original fabrication process. The here-proposed and validated three-dimensional integration scheme exploits selective lateral thermal oxidation of aluminiumrich AlGaAs layers. Compared with the previously reported processing techniques, this new scheme is simpler as it does not require any planarization or substrate transfer steps. As a proofof-principle demonstration of this approach, 250-µm diameter microdisk devices exhibiting quality factor reaching ∼8500 have been successfully fabricated.

In this paper, an iterative method to model the anisotropic lateral oxidation of circular structures is proposed and validated by confrontation to experimental data. The described model enables the efficient calculation of the temporal bi-dimensional evolution of the oxidation front shape, starting from a circular mesa, and progressing inward as a result of an anisotropic process combining an isotropic diffusion with an anisotropic reaction. The result of the developed model shows that the oxide aperture smoothly deforms from a circle to become more diamond-like, mimicking the experimental situation encountered when fabricating Vertical-Cavity Surface-Emitting Lasers (VCSELs) on (100) wafers or, more generally, when oxidizing circular mesas of aluminum-containing III-V semiconductor on similarly oriented substrates.

We report experimental and theoretical results on the lateral wet oxidation of bidimensional thin aluminum-rich layers into AlOx. We introduce a reaction-diffusion model of oxidation front propagation that includes effects of anisotropies and compare it to experimental results. This model can be used with any starting geometry, possibly nonconvex, and is deduced from the chemical reactions of wet oxidation of Al x Ga 1−x As -based layers. Numerical simulations performed with simple and complex geometries are in excellent agreement with the experimental observations. Our method is general and can apply to other oxides. It opens the way to the fine control of wet-oxidation fronts and to the formation of AlOx layers with a desired geometry that has numerous practical and relevant applications for, e.g., waveguiding or carrier confinement in photonics.

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Integrated whispering-gallery mode resonators are attractive devices which have found applications as selective filters, low-threshold lasers, high-speed modulators, high-sensitivity sensors and even as nonlinear converters. Their performance is governed by the level of detrimental (scattering, bulk, bending) loss incurred and the usable loss represented by the coupling rate between the resonator and its access waveguide. Practically, the latter parameter can be more accurately controlled when the resonator lies above the access waveguide, in other words, when the device uses a vertical integration scheme. So far, when using such an integration technique, the process involved a rather technically challenging step being either a planarization or a substrate transfer step. In this presentation, we propose and demonstrate an alternative method to fabricate vertically-coupled whispering-gallery mode resonators on III-V semiconductor epitaxial structures which has the benefit of being planarization-free and performed as single-side top-down process. The approach relies on a selective lateral thermal oxidation of aluminum-rich AlGaAs layers to define the buried access waveguide and enhance the vertical confinement of the whispering-gallery mode into the resonator. As a first experimental proof-of-principle of this approach, 75 µm-diameter micro-disk devices exhibiting quality factor reaching ~4500 have been successfully made.

The III-V semiconductor /oxide technology has become the standard fabrication technique for Vertical-Cavity Surface-Emitting Lasers. Current research aims to further enhance the performance of these emitters and diversify the range of devices that can be made using this technology. In this paper, we present a new model of the oxidation process which includes the anisotropic behaviour observed during conventional lateral oxidation. Furthermore, we demonstrate that this technology can be used as an innovative method to make micro-disk resonators with vertically-coupled access waveguides, an approach which can be generalised to fabricate other types of multi-plane photonic devices.