Heteroepitaxial growth of GaN on sapphire substrates by high temperature vapor phase epitaxy

•The deposition of GaN layers on sapphire substrates by HTVPE is demonstrated.•A new gallium evaporation cell for a reduced impurity concentration is presented.•An advanced multi-step process for the growth of GaN layers by HTVPE is described.•HTVPE layers ready for use as seeds are presented.•Overgrowth of HTVPE seed layers with increased growth rates is demonstrated.