Internal Microstrain and Distribution of Composition and Cathodoluminescence over Lapped Al[sub x]Ga[sub 1 – ][sub x]N Epilayers on Sapphire.

Structural properties and spatial inhomogeneity of MOCVD-grown Al[sub x]Ga[sub 1-x]N layers on (0001) sapphire substrates were studied. A nonuniform distribution of Al across the epilayer was observed in layers grown at constant flux rates of precursors. The model of compositionally graded layer formation is proposed on the basis of cathodoluminescence and X-ray data. It is established that homogeneous samples can be obtained by increasing the flux rate of trimethylaluminum at the initial stage of epilayer growth compared with that in all further stages. Lowering the growth rate reduces strain in epitaxial Al[sub x]Ga[sub 1-x]N layers. The influence of strain on the luminescence properties of the layers is discussed. [ABSTRACT FROM AUTHOR]