Infrared dielectric functions and crystal orientation of a-plane ZnO thin films on r-plane sapphire determined by generalized ellipsometry

Abstract Generalized infrared spectroscopic ellipsometry for wave numbers from 370 to 1200 cm −1 was applied to study the anisotropic dielectric response of wurtzite-type ZnO thin films grown on r -plane sapphire. Combined wavelength-by-wavelength analysis of data measured at multiple sample in-plane orientations allows for simultaneous extraction of the dielectric function (DF) tensor, the film thickness and the respective ZnO c -axis orientation, specifically in relation to the sapphire substrate. For anisotropic materials and use of generalized ellipsometry, the correlation problem between thickness and DF does not exist. Subsequent line shape analysis of ordinary and extraordinary DFs provides complete A 1 - and E 1 -symmetry longitudinal and transverse optical phonon-mode and broadening parameters, together with the static dielectric constants. The epitaxial relations from the ellipsometry data analysis are (1 1 −2 0) ZnO ∣∣(0 1 −1 2) sapphire and [0 0 0 1] ZnO ∣∣[0 −1 1 1] sapphire , which was confirmed by XRD measurements.