We study the influence of the reactor geometry and the control of the paras
itic deposits on the growth of GaN by HVPE. Growth rates around 100 mu m/h
have been obtained with gas outlets close to the substrate and 16 mu m/h wi
th homogeneous vapour. The quality of the epitaxial layer deteriorates whil
e the growth rate increases with decreasing distance between gas outlets an
d substrate, and the increase of the parasitic deposit. We predict by a mod
el that in a homogeneous vapour and for a deposited mass on the quartz wall
up to 0.86 g/h, the growth rate decreases drastically at high temperature
down to etching. Adding HCl to the main nitrogen now, the parasitic deposit
decreases and the growth rate stays constant.