Stable Optical Quality SiO2/TiO2 Stack Development for the Facet Coating of Laser Diodes

Titanium oxide in combination with Silicon dioxide is extensively used for the facet coating of laser diodes besides other applications for high reflectance coating. Stable stoichiometric TiO2 film deposition is very challenging with the conventional reactive e-beam deposition and often oxygen deficiency is observed in the deposited film, and hence the optical constants of the film are much inferior to the bulk crystalline TiO2. This oxygen deficiency is also observed in case of SiO2 film but is less pronounced than that of TiO2. Stoichiometric TiO2 film is deposited by ion beam sputtering and incorporated in the SiO2/TiO2 stack deposited on GaAs (100) substrate to evaluate their suitability for high reflectance coating application. The exact composition of the TiO2 film is evaluated by X-ray photoelectron spectroscopy (XPS) technique. The surface roughness of the SiO2 and TiO2 film deposited on GaAs (100) is measured by atomic force microscopy (AFM). The interface and surface roughness; the thicknesses of the individual layers are evaluated by X-ray reflectivity (XRR) technique. The reflectance of the SiO2/TiO2 bi-layer is measured by UV-Visible-NIR spectrophotometer. The high quality of the films with low level of interface roughness, good stoichiometry and stable layer thickness were established by the above measurements.