The influence of small amounts of added HCl during MOVPE growth of GaN and AlN in a hot-wall reactor is investigated. It is observed that parasitic precursor losses in the gas phase are suppressed, enabling crystal growth with large growth rates at elevated pressures. For the growth of GaN, only a small ratio of HCl to TMGa is necessary. This ratio is independent of the total TMGa flow rate but rises with increasing reactor pressure. For too high HCl-to-TMGa ratios, a reduced growth rate of GaN is observed. For the growth of AlN, a much higher HCl-to-TMAl ratio is needed. At this condition the same growth rate with a uniform deposition profile at a quadrupled reactor pressure is achieved, for otherwise unchanged flow conditions. (c) 2012 Elsevier B.V. All rights reserved.