Comparison of in situ optical reflectance and post-growth characterisation for quantitative composition and thickness determination of AlxGa1-xAs

We assess the use of normal incidence in situ laser reflectometry (LR) to give reliable quantitative composition and thickness information during epitaxial growth of a full range of AlxGa1-xAs (0.1⩽x⩽0.9) alloys on GaAs. It is shown that, provided the optical constants (n and k) are known accurately at the growth temperature, LR gives accurate results for both layer thickness and composition. Post-growth layer thickness measurements on cleaved edge cross section and wedge section TEM samples are more accurate than LR, but LR gives a much more accurate determination of composition than energy dispersive X-ray analysis on cross-sectional TEM samples and from thickness fringe analysis on wedge TEM samples. The relative advantages of LR and post-growth analysis are discussed.