Electron transport properties of GaN epilayers grown by metal-organic chemical vapor deposition

N-type GaN epilayers were grown on sapphire using the metalorganic chemical vapor deposition (MOCVD). Unintentionally doped GaN epilayers were grown as a functions of GaN buffer layer growth rate. The growth rate was found to be crucially related with the edge-type threading dislocations, and the dislocation density of ∼2×10 ⁸ cm ^-2 was obtained at the optimum condition. The thin epilayers with higher dislocation density require a two-band model including the Γ and the impurity bands in analysing the temperature-dependent Hall effects measured in a wide range 20∼800 K. But the two-band model was necessary only for temperatures lower than 300 K for doped epilayers. The thickness-dependent characteristics indicates that the impurity-band effects are ascribed to the near-interface region in unintentionally doped GaN layers.