Optical properties of AlN/sapphire grown at high and low temperaturesstudied by variable angle spectroscopic ellipsometry and micro Raman scattering,

摘要

Abstract: Variable angle spectroscopic ellipsometry (VASE) and micro Raman scattering have been employed to study the optical anisotropy and optical constants of AlN films grown at high and low temperature (HT and LT). The AlN films were grown by metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) on c-plane sapphire ($alpha@-Al$-2$/O$-3$/) substrates, respectively. Anisotropic optical phonon spectra of AlN have been measured along two directions so that the optical axis $LS@c$GRT of AlN is either perpendicular or parallel to the polarization of the incident beam. Nonzero off-diagonal elements A$-ps$/ and A$-sp$/ of Jones matrix in the reflection VASE (RVASE) measurements indicate that the $LS@c$GRT of AlN is slightly away from surface normal due to substrate miscut. The ordinary optical constants of both HT AlN have been determined spectroscopic ellipsometry at small angles of incidence so that the extraordinary response is greatly reduced. The film thickness along with the surface overlayer was determined via the VASE data analysis as well. !17