Layers of AlBN were grown on sapphire by organometallic vapor-phase epitaxy at 1050 °C using triethylboron, trimethylaluminum, and ammonia as precursors. It is shown that boron is readily incorporated into the layers and its concentration in the solid phase can be as high as 40&percent;. However, single phase Al1−xBxN films can only be grown for compositions not exceedingx=0.01. For higher boron concentrations in the solid the second B-rich phase is formed. This phase was identified as wurtzite BN based on the results of transmission electron microscopy and x-ray diffraction. The growth of this thermodynamically unfavorable phase becomes possible, most probably, because it occurs within the framework provided by wurtzite AlN islands first formed on the surface and setting up the sites for lateral growth of wurtzite BN. That leads to formation of columnar structure of AlN and BN crystallites oriented in the basal plane and existing side by side. ©1997 American Institute of Physics.