Spectroscopic ellipsometry of epitaxial ZnO layer on sapphire substrate

Optical properties of epitaxial ZnO layers have been studied in the spectral region from 1.5 to 5.4 eV using four-zone null spectroscopic ellipsometry. An existing model dielectric function based on excitonic structure near direct band gap has been improved by including a high-energy absorption term. Surface layer, corresponding to the surface roughness, was found to be essential to fit the spectroellipsometric data obtained. Two kinds of samples have been studied: ZnO layers prepared on (0001) and (11 (2) over bar 0)- oriented sapphire substrates. The surfaces of the first ones were found to be more rough. (C) 2000 American Institute of Physics. [S0021-8979(00)01911-3].