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

Abstract

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