| Résumé | The first stages of stress relaxation have been studied in a series of 2% tensile strained (In, Ga)(As, P) films of various compositions by transmission electron microscopy. Ternary In1-x Ga x As and In1-x Ga x P films relaxed by a combination of twinning and cracking, while the quaternary In1-x Ga x As1-y P y film relaxed only by twinning. The differences between the behaviours of the ternary and quaternary systems were correlated with the surface topography of the films. The surface nucleation of 90° partial dislocations was shown to be feasible at the growth temperature of the films (480°C) in the presence of surface roughness but, in the absence of a critical roughness, cracking was the preferred mechanism for coherency loss. The critical film thicknesses observed for stress relaxation by either twinning or cracking were shown to be in good agreement with the calculated values. The twins themselves often terminated inside the substrate (InP) rather than at the substrate-film interface. This behaviour was related to the elastic mismatch that exits between the harder film and softer substrate. |
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