Optical absorption near the band edge in GaN grown by metalorganic chemical-vapor deposition

The optical absorption near the fundamental absorption edge in GaN thin films grown on sapphire substrates using the metalorganic chemical-vapor deposition technique is studied as a function of temperature. The absorption spectrum shows a free-exciton peak at 353.55 nm and a shoulder at 354.67 nm, which is attributed to a bound exciton. The absorption band edge was determined from the energy position of the exciton line observed in the entire temperature range of 13--300 K. The band-edge energies determined in this temperature range were fitted with the Varshni empirical relationship Eg(K)=Eg(0)-{σ}T²/(T+θD) and with the expression Eg(K)=Eg(0)-{κ}/[exp(θE/T)-1]. The results show that θD{}737.9 K in agreement with the calculated value. {} 1996 The American Physical Society.