Optical Properties of GaN and Other III-Nitride Semiconductor Materials Studied by Variable Angle Spectroscopic Ellipsometry

摘要

In this 2-year project, we have determined anisotropic optical dielectric functions of GaN, AlN and Sapphire. It is for the first time, the ordinary and extraordinary optical constants of the important III-Nitride materials, GaN, AlN and sapphire, have been determined by variable angle spectroscopic ellipsometry (VASE), in the energy range of 0.75 eV to 6.5 eV. Our results indicate that anisotropic optical properties are important feature of the GaN and other hexagonal structured III-nitride materials. The extraordinary optical properties of those materials, which were omitted before, influence in many ways the optoelectronic devices properties made from GaN, AlN etc. We have also discovered a method to characterize the ordinary and extraordinary dielectric optical functions by VASE under c-plane direction. Our method indicates that the ordinary optical dielectric functions (E perpendicular to (c)) can be precisely determined by the isotropic mode VASE measurements at small angles of incidence, e.g., between 20 and 40 degrees, while the anisotropic dielectric functions (E // (c)) can be detected most-sensitively at large angles of incidence (near the pseudo-Brewster angle).