Reasonable quality Si-doped (11 (2) over bar0) a-plane GaN have been grown by metalorganic chemical vapor deposition on (1 (1) over bar 02) r-plane sapphire substrates. Optical properties of the films were studied by photoluminescence spectroscopy. Our experimental results suggest that not V-Ga but the VGa-ON Complex is the key defect responsible for yellow luminescence in GaN. At 12.9 K, free exciton A, donor bound exciton and exciton bound to neutral acceptor (I-x), which are similar to (0001) GaN are observed. Different to (0001) GaN, the longitudinal optical and transverse optical phonon replicas are found emerging simultaneously. Another peak at 3.42 eV is interpreted as donor-acceptor pair transition. (C) 2003 Elsevier B.V. All rights reserved.