Infrared characterization of GaN and GaN/AlGaN molecular beam epitaxial layers

An infrared reflection technique has been developed for the characterizatio n of GaN and GaN/AlGaN epitaxial layers and multilayers. The infrared light is brought to the III-nitride surface with a KRS-5 internal reflection cry stal. The technique is complimentary to Raman measurements and provides inf ormation on the longitudinal and transverse optical (LO) modes of GaN and A LN. For thin GaN layers, the modes of the thin, 22-nm-thick A1N nucleation layer can be clearly observed in the spectra. The free carrier concentratio n of the GaN can be characterized by analyzing the LO phonon-plasmon couple d mode present in doped samples. Because the light is multiply reflected in the GaN layer, the technique can potentially detect impurities (such as H or C) in the GaN. The application of this technique to characterize high qu ality molecular beam epitaxial layers is discussed. (C) 2000 American Vacuu m Society. [S0734-2101(00)04302-5].