Optical determination of InxGa1-xAs composition on InP using a Fabry-Perot test structure

Previously we reported on an ex-situ optical reflectance technique for determining precise epilayer thicknesses and Al_xGa_1-xAs composition using a Fabry-Perot test structure. The use of the test structure with the resulting high reflectivity modulation was critical for obtaining the high precision. In this paper, we extend the technique to determine the composition and the lattice mismatch of In_xGa_1-xAs epilayers grown on InP substrates. In our technique, a stack consisting of 7 pairs of In _xGa_1-xAs/InP and a cavity layer are grown on an InP wafer. The optical reflectance spectrum from a 2 mm spot is then measured and fitted to a transfer matrix model to extract the composition and thickness. The selection ofthe wavelength range of 1600 nm to 2200 nm was critical for extracting the In_xGa_1-x As properties uniquely. The advantage of using this reflectance fitting technique over other conventional methods is the simplicity of the instrumentation and the potential for fast measurement speed (~1 sec per point)