Possibility of AlN growth by MOVPE in a planetary reactor with high growth rate was investigated. Growth was performed on (0001) Al2O3 substrates at the reactor pressure of 100 mbar. It was shown that deposition rate is close to diffusion limit at low NH3 flows and reduces abruptly above a certain threshold value of NH3 due to gas-phase parasitic reactions. At constant Will ratio of 1.5-2, AlN growth rate dependence on TMAI flow was linear and a maximum growth rate of 8.6 mu m/h was achieved. Process modeling allowed predicting and explaining the trends related to the onset of parasitic chemistry for various Will ratios and other growth conditions. Surface morphology planarization was achieved by either (1) NH3 flow rate reduction or (2) TMGa injection after the layer with thickness of 75-300 urn was grown. The second approach looks more fruitful resulting in atomically flat Al(Ga)N layers with a 2 mu m/h growth rate. For the conditions (high temperature, low NH3 and high H-2 concentration) used Ga acts mostly as surfactant (Ga content in Al(Ga)N is about 3-5%). (c) 2011 Elsevier B.V. All rights reserved.