Optical characterisation of interface properties for hexagonal GaN grown by MBE on GaAs

摘要

A new optical method for the characterisation of substrate/film interface properties of GaN grown on GaAs is presented. It is based on reflectivity measurements over an extended spectral range. The influence of surface roughness is separated by a comparison of the experimental data with calculations for a smooth film above the band gap of GaN, while at lower energies, the deviations from the calculated one-layer behaviour (without interface) are strongly correlated to the effective refractive index of the interface n_(int) and its thickness. It is shown that for GaAs substrates under certain MBE growth conditions, n_(int) is mainly determined by the void fraction.