A method for growing bulk GaN and AlGaN single crystal boules, preferably using a modified HVPE process, is provided. The exercise weight has a relatively narrow profile, or width, to avoid contact with the body during exercise. For this purpose, the guide vane platforms 9, 10 possess, on both sides, prolongations 9, 10, in the direction of the respectively adjacent moving blade row 1 and extend into the region delimited by its sealing ribs 3 and 4.