In this paper, we report the characteristics of GaN heteroepitaxial films grown on Si(111) at 700 degrees C using plasma-assisted metalorganic chemical vapour deposition (PA-MOCVD). In this growth technique, H-2 plasma was used in addition to N-2 plasma. Two sets of samples with different buffer layers were used, i.e. GaN and AIN buffer layers. In the infrared region both samples exhibit similar reststrahlen band shape. However the sample with GaN buffer layer exhibits better optical properties in the visible region compared with its counterpart. This is attributed to its better structural bulk and surface properties.