AlN is a promising substrate materials for AlGaN-based ultraviolet light emitting diodes, because of its high thermal conductivity, high ultraviolet transmittance and small lattice mismatch with AlGaN layers. Heteroepitaxial growth techniques of AlN layer on sapphire substrates should be improved to satisfy the increasing demand for large-size sapphire substrates. Recently, we have developed a new liquid phase epitaxial growth technique to grow AlN films on the nitrided sapphire using Ga-Al fluxes. Influential factors such as flux composition, growth temperature and crystal orientation of sapphire were studied. Details of the experimental results of the Ga-Al flux technique and its thermodynamic principle are introduced in this article.