SURFACE SPINODAL DECOMPOSITION IN LOW-TEMPERATURE AL0.48IN0.52 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 bee n investigated by ex-situ transmission electron microscopy (TEM) and i n-situ scanning tunnelling microscopy (STM). For a growth temperature of 450 degrees C, a V/III beam equivalent pressure (BEP) ratio equal t o 20 and a growth rate of 1 mu m h(-1), the clusters are strongly anis otropic: typically, 2 nm along the [110] direction, 30-50 nm along the [<1(1)over bar>0] direction and 20 nm along the [001] direction. We s how theoretically that such a spinodal decomposition would be forbidde n if the surface of the deposited film is perfectly flat. We also demo nstrate that this decomposition appears to be possible if the surface roughness is sufficient to allow a partial elastic relaxation. (C) 199 8 Elsevier Science B.V.