Comparison of in situ optical reflectance and post-growth characterisation for quantitative composition and thickness determination of Al xGa 1- xAs

Abstract

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 Al x Ga 1- x As (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.