Surface spinodal decomposition in low temperature Al0.48In0.52As grown on InP(001) by molecular beam epitaxy

The clustering development for lattice-matched Al0.48In0.52As grown on (001) oriented InP substrates by molecular beam epitaxy (MBE) has been investigated by ex-situ transmission electron microscopy (TEM) and in-situ scanning tunnelling microscopy (STM). For a growth temperature of 450°C, a V/III beam equivalent pressure (BEP) ratio equal to 20 and a growth rate of 1 μm h−1, the clusters are strongly anisotropic: typically, 2 nm along the [110] direction, 30–50 nm along the [11¯0] direction and 20 nm along the [001] direction. We show theoretically that such a spinodal decomposition would be forbidden if the surface of the deposited film is perfectly flat. We also demonstrate that this decomposition appears to be possible if the surface roughness is sufficient to allow a partial elastic relaxation.