The effect of nucleation coalescence upon the crystalline quality of AlN films, grown onto sapphire by plasma-assisted molecular beam epitaxy, was investigated. The coalescence rate was controlled by the V/III ratio chosen for the growth after nucleation. Slightly Al-rich conditions, corresponding to slow coalescence, could significantly reduce the density of edge threading dislocation, which were predominant in AlN epilayers. Cross-sectional transmission electron microscopic images of the AlN epilayer grown under these conditions clearly revealed an automatically formed boundary where an abrupt decrease in edge threading dislocation density occurred.

Improvement of AlN Film Quality by Controlling the Coalescence of Nucleation Islands in Plasma-Assisted Molecular Beam Epitaxy. C.Zhang, Z.B.Hao, F.Ren, J.N.Hu, Y.Luo: Chinese Physics Letters, 2010, 27[5], 058101