In situ spectroscopic ellipsometry of MOCVD-grown GaN compounds for on-line composition determination and growth control

Abstract

In situ spectroscopic ellipsometry measurements were performed in the ultraviolet–visible spectral range during the growth of GaN and ternary compounds in a metal organic chemical vapor deposition reactor and compared with standard reflectivity data recorded in parallel. Special emphasis has been given to the characterization of the GaN nucleation layer formed on sapphire substrates, its annealing and the subsequent initial stages of GaN growth. Furthermore, the optical response of GaN and ternary compounds (AlGaN, InGaN) has been studied as a function of the substrate temperature up to 1200°C. In the context of the on-line monitoring of ternary alloy concentration, ellipsometric data has been recorded as a function of time (increasing thickness) during the growth of AlGaN with different Al content and displayed on the plane of the complex dielectric function. The resulting exponential spirals gave, at the convergence points, the optical constant of the growing material and, therefore, an evaluation of the composition already achieved at the beginning of the growth process.