THE INFRARED OPTICAL FUNCTIONS OF ALXGA1-XN DETERMINED BY REFLECTANCESPECTROSCOPY

Infrared reflectivity measurements have been carried out on samples wi th structures of GaN/sapphire and AlxGa1-x/N/GaN/sapphire as well as s apphire substrates. Analyses of the reflectance data of sapphire using the Kramers-Kronig technique and fitting of the reflectance spectra o f GaN and AlxGa1-xN samples using analytical expressions have been mad e. The high-frequency dielectric constant epsilon(alpha) and the trans verse phonon frequency omega(TO), are found to vary from 5.15 to 4.2 a nd from 559.7 to 586.3 cm(-1), respectively, when the composition x is varied from 0 to 0.35 at room temperature. The E2 mode, which arises from the disordered stale of the alloys, has been observed in the refl ectivity spectrum of AlxGa1-xN, and the intensity of the peak is enhan ced by increasing the Al content. (C) 1998 American Institute of Physi cs.