Tailoring of embedded dielectric alumina film in AlGaAs epilayer by selective thermal oxidation

Vertical optical confinement is a critical requirement for a wide range of III-V photonic devices where Al2O3 material is the typical oxide used due to its low refractive index. This oxide layer can be formed from the oxidation of AlAs in an epitaxial GaAs/AlAs/GaAs or AlGaAs/AlAs/GaAs stack, with the advantage that the top layer remains single-crystalline. The thick film oxidation of AlAs is required for photonic applications. In this article, we report the oxidation processes developed to fully convert AlAs to AlOx films by analyzing both thin (100 nm) and thick (500 nm) AlAs films on GaAs (001) and 2° miscut GaAs (111)A substrate. Systematic microscopic characterization is performed to demonstrate the absence of any delamination at the oxide interfaces and the evolution of the diffusive oxidation process microscopically characterized is compared with an optical (µ-Raman) characterization. We demonstrate the selectivity of the AlAs oxidation process with respect to the active Al0.18Ga0.82As layer and the GaAs substrate. Finally, the proposed method is adopted to create a high refractive index contrast between the active optical material and the environment in the specific case of a III-V photonic crystal device, highlighting the potential of this approach for non-linear photonic applications.