Relationships are studied governing the Raman scattering spectra in GaN nanocrystals grown by HVPE on substrates of oxidized silicon with Ag atoms deposited in a UHV system. It is found that the intensity of an LO-phonon-plasmon coupled mode in GaN nanocrystals is increasing initially as metal atoms are deposited on their surface to a thickness of 3 nm and then decreasing. It is suggested that the intensity increase of this mode is due to increasing near-surface barrier height and the space-charge layer width. (C) 2004 Elsevier B.V. All rights reserved.