Infrared properties of bulk GaN

Transmission and reflection measurements in the frequency range (700-2000 c m(-1)) have been carried out on high-quality bulk GaN grown by the sublimat ion technique. The transmission spectra are polarization dependent and show combination bands arising from anharmonic forces. The combination absorpti on is much stronger for E parallel to c polarization than that for E perpen dicular to c polarization. A high value of 350 cm(-1) for the absorption co efficient in the combination band can be explained by the strong anharmonic forces in GaN. (C) 1999 American Institute of Physics. [S0003-6951(99)0161 9-8].