Optical scatter in epitaxial semiconductor multilayers

We report measurements of optical scatter in epitaxial semiconductor multilayer structures. The structures comprise quarter-wave layers of Al0.2Ga0.8As/AlAs and GaAs/AlAs grown by molecular beam epitaxy and Al0.2Ga0.8As/AlAs grown by metalorganic chemical vapor deposition to assess differences due to growth technique and layer composition. The bidirectional reflective distribution function (BRDF) is measured at a wavelength of 835 nm corresponding closely to the Bragg reflection condition of the multilayer. The BRDF measurement yields calculated values for the total integrated scatter and effective surface roughness. The former is in the range 7×10−4–5×10−3 while the latter is typically 3–16 Å over the spatial frequency range 3×10 −2–1 μm−1. Both growth techniques yield comparable scatter loss on average, but there are significant differences in microscopic surface morphology, uniformity of scatter across the wafer, and lower limits of scatter. The measurements have significant implications for applications such as surface-emitting laser technology.