The first stages of stress relaxation were studied, by transmission electron microscopy, in a series of tensile-strained (2%) films having various compositions. It was found that ternary InGaAs and InGaP films relaxed via a combination of twinning and cracking, whereas quaternary InGaAsP films relaxed only by twinning. The differences between the behaviours of the ternary and quaternary systems were related to the surface topography of the films. The surface nucleation of 90° partial dislocations was shown to be feasible at the growth temperature (480C) of the films in the presence of surface roughness. However, in the absence of a critical degree of roughness, cracking was the preferred mechanism of coherency loss. The critical film thicknesses for stress relaxation via twinning or cracking were in good agreement with calculated values. The twins often terminated within the InP substrate, rather than at the substrate/film interface. This was attributed to the elastic mismatch that existed between the hard film and soft substrate.

The First Stage of Stress Relaxation in Tensile Strained InGaAsP Films. X.Wu, G.C.Weatherly: Philosophical Magazine A, 2001, 81[6], 1489-506