The refractive index and extinction coefficient of cubic GaN in the energy
range of 1.5-3.7 eV were determined with high accuracy using combined refle
ctivity and spectroscopic ellipsometry studies of layers grown by molecular
beam epitaxy on GaAs(001). A comparison of the experimental reflectivity d
ata with theoretical calculations demonstrates that the data analysis has t
o be performed by taking into account both surface roughness and a nonabrup
t substrate-film interface. In the transparent region the refractive index
of cubic GaN was found to be slightly higher than that of the hexagonal mod
ification. (C) 1999 American Institute of Physics. [S0021-8979(99)02501- 3]
.