Abstract: Embodiments of the invention generally relate to methods for forming Group III-V materials by a hydride vapor phase epitaxy (HVPE) process. In one embodiment, a method for forming a gallium nitride material on a substrate within a processing chamber is provided which includes heating a metallic source to form a heated metallic source, wherein the heated metallic source contains gallium, aluminum, indium, alloys thereof, or combinations thereof, exposing the heated metallic source to chlorine gas while forming a metallic chloride gas, exposing the substrate to the metallic chloride gas and a nitrogen precursor gas while forming a metal nitride layer on the substrate during the HVPE process. The method further provides exposing the substrate to chlorine gas during a pretreatment process prior to forming the metal nitride layer. In one example, the exhaust conduit of the processing chamber is heated to about 200° C. or less during the pretreatment process.