Methods and apparatus for depositing thin films incorporating the use of a surfactant are described. Methods and apparatuses include a deposition process and system comprising multiple isolated processing regions which enables rapid repetition of sub-monolayer deposition of thin films. The use of surfactants allows the deposition of high quality epitaxial films at lower temperatures having low values of surface roughness. The deposition of Group III-V thin films such as GaN is used as an example.