Growth of AlGaN in AIX2000 HT planetary reactor was investigated under the wide range of NH3, TMAI and TMGa flows. At low NH3 flows gallium incorporation in AlGaN is suppressed by surface chemical process of Ga-containing nitrides decomposition in presence of hydrogen. The rate of this reaction strongly depends on NH3, H-2 and TMAI flows. At high NH3 flows influence of hydrogen on epitaxial process is less pronounced but strong gas-phase parasitic reactions results in both aluminum and gallium losses which limit the achievable growth rate and aluminum content in the layer. Adjustment of reactor conditions lets to reach growth rates of 2-3 mu m/h for AlGaN layers in the whole composition range and 5-6.5 mu m/h in the range of Al content of 25-50%. (c) 2012 Elsevier B.V. All rights reserved.