Internal microstrain and distribution of composition and cathodoluminescence over lapped Al(x)Ga(1-x)Nepilayers on sapphire

Structural properties and spatial inhomogeneity of MOCVD-grown AlxGa1- xN l ayers on (0001) sapphire substrates were studied. A nonuniform distribution of Al across the epilayer was observed in layers grown at constant flux ra tes of precursors. The model of compositionally graded layer formation is p roposed on the basis of cathodoluminescence and X-ray data. It is establish ed that homogeneous samples can be obtained by increasing the flux rate of trimethylaluminum at the initial stage of epilayer growth compared with tha t in all further stages. Lowering the growth rate reduces strain in epitaxi al AlxGa1- xN layers. The influence of strain on the luminescence propertie s of the layers is discussed. (C) 2000 MAIK "Nauka/ Interperiodica".