Anisotropic surface morphology in a tensile-strained InAlAs layer grown on InP(100) substrates

The anisotropic surface morphology of a tensile-strained In0.42Al0.58As layer grown on an InP(100) substrate was investigated by means of observing the cross-hatch patterns between two orthogonal in-plane directions: [011] and 01¯1. Analysis results using atomic force microscopy evidently reveal a higher array density along direction [011], with an asymmetrically sharp ridge across each array. Conversely, there was a much lower array density along direction 01¯1 and a symmetrically big mound-like ridges. Our X-ray diffraction and energy-dispersive spectroscopy analyses showed a more substantial amount of strain relaxation along direction 01¯1 due to preferential indium incorporation along [011]. As a result, the big mound ridges over the arrays along direction 01¯1 were believed to be the result of local indium accumulation. Additionally, microcrack formations, penetrating into substrates, were exclusively formed on top of the mound ridges with central depressions along direction 01¯1, presumably causing additional anisotropic strain relaxation.