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 E(g)(K) = E(g)(0) - sigma T-2/(T + theta(D)) and with the expression E(g)(K) = E(g)(0)-kappa/[exp(theta(E)/T) - 1]. The results show that theta(D) similar or equal to 737.9 K in agreement with the calculated value.