High reflectivity monolithic sub-wavelength diffraction grating with GaAs/AlOx stack

This paper presents the fabrication of high reflective sub-wavelength gratings in GaAs on wet oxidized AlxOy low index layers. This structure can efficiently replace a top Bragg reflector in GaAs-based vertical cavity lasers (VCSELs), while keeping all the advantages of a monolithic stack. Low refractive index and low loss can be achieved with the oxide sublayer, thus providing a high reflectivity over a large wavelength range. Reflectivities above 90% have been measured with stopbands exceeding 130 nm. Further adjustments of the geometrical parameters will enable the reflectivity requirements to be fulfilled for implementation in microcavity devices