The effect of crystalline quality of undoped a-plane GaN buffer layers on the properties of Si-doped GaN layers grown with different doping levels was investigated. The dominant photoluminescence (PL) emission at about 3.42 eV (D-1 band) for all Si-doped GaN samples was associated with excitons bound to basal stacking faults (BSFs). The intensity ratio of the D-1 band to near band edge (NBE) emission was reduced with increasing doping concentration, associated with the decrease in the density of BSFs. Interestingly, it was also found that the intensity of the DAP-longitudinal optical (LO) phonon replica exceeded the DAP emission above 50 K, which might be related to the structural defect-related emission in Si-doped a-plane GaN samples. (c) 2012 Elsevier B.V. All rights reserved.