Determining refractive indices of III–V thin films from interference fringes in oblique reflectance spectra

The room-temperature dispersive refractive indices of GaSb and GaSb-matched AlAs0.08Sb across the 2–4.15 μm range are determined by a new approach to the analysis of interference fringes in reflectance spectra. This method utilizes linear regression of interference fringe positions over various oblique angles of incidence to remove the need for measurements to be taken at normal incidence. The presented refractive indices are validated by simulation of the reflectance spectrum of a distributed Bragg reflector. An alternative method is also presented, suitable for characterizing epilayers with low film thickness, such as those intended for epitaxial growth calibration. In such thin films, fewer interference fringes form within a given spectral range, prohibiting analysis by the primary method. The alternative method is applied to thin films of GaSb-matched GaInAsSb, extracting the dependence of the room-temperature static refractive index on increasing indium content.