THE CHARACTERISTICS OF STRAIN-MODULATED SURFACE UNDULATIONS FORMED UPON EPITAXIAL SI1-XGEX ALLOY LAYERS ON SI

When strained, continuous Si1-xGex alloy layers are prepared by epitaxial growth on Si substrates. the growth surface can become nonplanar. In the present work, combined transmission electron microscope and atomic force microscope studies are employed to reveal the detailed nature of the surface ripples and undulations which form. Under specific ranges of growth conditions, crystallographically aligned, interlocking ripple arrays are produced. TEM contrast studies demonstrate that well-defined, oscillatory strain variations accompany these ripple structures, the presence of which is shown to be associated with partial elastic strain-relief and lowering of the energy of the strained-layer system. It is also demonstrated that the tipper surface of a Si cap deposited on such a layer rapidly becomes planar with increasing thickness, this being likely to result from the reduction in surface energy so achieved.