Morphological breakdown during growth of a high nitrogen content GaInNAs thin film

The breakdown in surface morphology during the growth of an 8 nm thick Ga0.7In0.3N0.05As0.95 layer has been investigated by scanning tunnelling microscopy. During initial growth (<0.5 nm) the alloy layer is planar but strained. Lateral composition modulation due to spinodal decomposition leads to the co-existence of tensile strained N-rich regions and compressively strained N-poor regions, creating an oscillatory strain field (OSF) across the surface. The overall strain increases with layer thickness up to ∼0.5 nm, after which it is relieved by a transition from two-(2D) to three-dimensional (3D) growth, which manifests itself as an undulating, pitted layer. We propose that the region at the bottom of each pit is N-rich and that overgrowth of such regions is inhibited, thereby avoiding the strain caused by lattice mismatch. The results offer insight into the mechanisms involved in the breakdown of the 2D growth of thin dilute nitride layers at relatively high N concentrations.