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 ${\mathit{E}}_{\mathit{g}}$(K)=${\mathit{E}}_{\mathit{g}}$(0)-σ${\mathit{T}}^2$/(T+${\mathrm{\theta }}_{\mathit{D}}$) and with the expression ${\mathit{E}}_{\mathit{g}}$(K)=${\mathit{E}}_{\mathit{g}}$(0)-κ/[exp(${\mathrm{\theta }}_{\mathit{E}}$/T)-1]. The results show that ${\mathrm{\theta }}_{\mathit{D}}$≃737.9 K in agreement with the calculated value. © 1996 The American Physical Society.