It was recalled that it had been shown elsewhere that the room-temperature yield pressure of InxGa1-xAs superlattices, measured by nano-indentation, decreased from a high value as the volume averaged strain modulation was increased. At 500C, under uniaxial compression or tension, the yield stress increased from a low value with increasing strain modulation. Cross-sectional transmission electron microscopy was used to examine the deformation mechanisms in these 2 loading regimes. At room temperature, both twinning and dislocation flow was found; with the proportion of twinning decreasing with increasing strain modulation. The coherency strain of the superlattice was retained in a twin but partially relaxed by dislocation flow. The strain energy released by the loss of coherency assisted dislocation flow and weakened the superlattice. Twins were nucleated only when a critical elastic shear of about 7° was attained at the surface. The plastic zone dimensions under the indent were finite at the yield point, with a width and depth of approximately 1.3 and 1.1µm, respectively. Under uniaxial compression and tension at 500C, the superlattices deformed by dislocation were along {111} planes. The most highly strained samples also partially relaxed via the formation of misfit dislocations.

Effect of Coherency Strain on the Deformation of InxGa1-xAs Superlattices under Nano-Indentation and Bending. S.J.Lloyd, K.M.Y.Png, W.J.Clegg, A.J.Bushby, D.J.Dunstan: Philosophical Magazine, 2005, 85[22], 2469-90