LATTICE DISTORTION IN DRY-ETCHED SI SIGE QUANTUM-DOT ARRAY STUDIED BY2D RECIPROCAL SPACE MAPPING USING SYNCHROTRON X-RAY-DIFFRACTION/

Using synchrotron X-ray two-dimensional reciprocal space mapping aroun d the (004) and (224) reciprocal lattice points, we have studied the c hanges of the lattice strain in a 30-period 3 nm Si/3 nm Si0.7Ge0.3 su perlattice (SL) that has been processed into a phi approximate to 50 n m columnar dot array by e-beam patterning combined with reactive ion e tching. It has been found that the superlattice within the columns was partially relaxed after nano-fabrication, The observation of high-ord er SL satellites from columnar dots indicates a good long-range orderi ng of SL layers. An analysis based on elastic theory showed that the s train relief in the superlattice occurs by a partial relaxation in SiG e layers together with a biaxial lattice expansion in the thin Si laye rs, i.e. a strain symmetrisation effect. A staggered band line-up betw een Si and SiGe is then expected. We propose that an enhanced recombin ation between electrons and holes confined in adjacent quantum wells a t the hetero-interfaces may give rise to the observed increase in the luminescence efficiency in this type of structures.