THE EFFECT OF BUFFER LAYERS ON STRUCTURAL QUALITY OF SI0.7GE0.3 LAYERS GROWN ON SI(001) SUBSTRATES BY MOLECULAR-BEAM EPITAXY

The effect of buffer layers on the structural quality of Si0.7Ge0.3 al loy films grown on Si(001) substrate by molecular beam epitaxy (MBE) h ave been characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and cross-sectional transmission electron microsco pe (XTEM). It is confirmed that the threading dislocation density in t he alloy layer drastically decreases by using buffer layers. The sampl es with step buffer layers relax the strain by introducing the disloca tions at the interfaces, part of which goes through the alloy layer. O n the other hand, the samples with superlattice buffer layers relax th e strain by introducing the dislocations in the buffer layers which te rminate at the interface of the superlattice buffer layer and the topm ost alloy layer. Tile residual strain in the alloy layers on buffer la yers grown at 550 degrees C is relaxed upon the annealing at 700 degre es C, or the growth at 700 degrees C.