OPTICAL-ABSORPTION NEAR THE BAND-EDGE IN GAN GROWN BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION

The optical absorption near the fundamental absorption edge in GaN thi n films grown on sapphire substrates using the metalorganic chemical-v apor deposition technique is studied as a Function of temperature. The absorption spectrum shows a free-exciton peak at 353.55 nm and a shou lder at 354.67 nm, which is attributed to a bound exciton. The absorpt ion band edge was determined from the energy position of the exciton l ine observed in the entire temperature range of 13-300 K. The band-edg e energies determined in this temperature range were fitted with the V arshni 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 ag reement with the calculated value.