Heteroepitaxial GaN films in general had very high concentration of defects and at the same time showed broad photoluminescence peaks at energies below the band-gap energy (3.4eV), i.e., the so-called yellow (YL) and blue luminescence (BL) centered at 2.2 and 2.9eV, respectively. The origin of these photoluminescence peaks was commonly attributed to defects. The present paper studies the relationship of the yellow and blue luminescence with the defect structure by a combination of photo-etching and photoluminescence. Nominally undoped (n-type) GaN layers were grown by metal organic chemical vapor deposition (MOCVD). By photo-etching the perfect material between defects was removed and defect-related nanocolumns were formed. Photoluminescence measurements of samples etched to various degrees allowed the identification of the different photoluminescence features. A fully etched sample showed no photoluminescence signature related to any of the band edge features and BL was quenched completely, while the yellow luminescence was attenuated only to the degree to which the volume amount of GaN was removed. Such behavior suggested that defects causing YL were not related to dislocations but were rather homogenously distributed throughout the layer in the form of point-like defects. The decrease of the BL intensity at 4.4K with excitation dose (bleaching) and the simultaneous increase in YL intensity for as-grown samples and the lack of such effects for etched samples imply a direct connection between the defect centers responsible for YL and BL.

Statistical Photoluminescence of Dislocations and Associated Defects in Heteroepitaxial GaN Grown by Metal Organic Chemical Vapor Deposition. L.Macht, J.L.Weyher, A.Grzegorczyk, P.K.Larsen: Physical Review B, 2005, 71[7], 073309 (4pp)