GaN films were grown on Si(100) substrate by atomic layer deposition (ALD) using GaCl3 and NH3. Growth conditions were identified for which the growth rate exhibited a plateau at ∼2.0 Å/cycle, consistent with self-limiting adsorption. A relatively wide temperature window (500–750 °C) for ALD growth mode was also established for one flow sequence schedule. In this limit, both the (0002) and (1011) orientations of GaN were evident, which was attributed to the competition between vertical and lateral growths. Cl incorporation was detected by x-ray photoelectron spectroscopy for samples prepared with long GaCl3 exposure time. It is postulated that gas phase formation of (ClGaNH)n with n=1–3 [Kovács, Inorg. Chem. 41, 3067 (2002)] results in higher Cl content.