STRAIN AND DEFECTS DEPTH DISTRIBUTIONS IN UNDOPED AND BORON-DOPED SI1-XGEX LAYERS GROWN BY SOLID-PHASE EPITAXY

A detailed characterization of undoped and heavily boron-doped Si1-xGe x layers with x=0.21, 0.26, and 0.34 grown on (001) Si wafers by solid phase epitaxy is presented. The starting material for solid phase epi taxial growth was prepared by amorphization of epitaxial SiGe-Si heter ostructures by ion implantation. In order to obtain doped layers, boro n was also implanted into some of the amorphous samples, After regrowt h, the strain depth distributions of the SiGe layers ular scans and th e defect distributions were observed by high-resolution electron micro scopy. A defect-free region ranging from 0 nm (undoped layer of x = 0. 34) to 30 nm (doped layer of x = 0.21) in thickness was observed next to the layer-substrate interface, In the upper region of the layers, s train-relieving defects, identified as planar faults, were observed. S ome isolated defects were also present at the layer-substrate interfac es of most of the samples. The measured strain depth profiles show tha t (i) the defect-free regions are not always fully strained; the defec ts located at the interfaces being responsible for this partial relaxa tion; (ii) the strain is almost constant throughout the defect-free la yers because it cannot be relieved due to the absence of defects; and (iii) the strain progressively decreases towards the sample surfaces i n the region of the layer where the strain-relieving defects are locat ed. Comparison between the undoped and boron-doped layers show the con sequences of the strain compensation effect due to the incorporation o f boron atoms into the lattice. The defect-free regions of the doped l ayers are thicker and closer to coherency than those in the undoped la yers of the same composition and the defect density in the upper regio n of the layers is significantly reduced, As a result of the strain co mpensation effect, a 30-nm-thick heavily doped layer with x=0.21 is fo und to be defect free and fully strained throughout its whole thicknes s although the corresponding undoped layer was partially relaxed and s howed strain-relieving defects. (C) 1997 American Institute of Physics .