Self organization of Ge dots on Si substrates: influence of misorientation

The growth of self organized fully strained Ge dots is accomplished by usin g a two step process which consists of depositing Ge dots on a periodic uni directional undulated Si1-xGex (118) template layer. The main reason for th is methodology is to make use of the stress driven step bunching that devel ops on a (118) surface (10 degrees off (001)). In this report we concentrat e on the growth mechanism of Ge on the Si1-xGex template layer. RHEED and T EM measurements were used to determine the 2D-3D growth transition as a fun ction of Ge coverage. We find that the onset of the 3D island formation cha nges from 4 to 7 ML on the (001) and (118) surfaces. respectively. While 3D islands are mainly isotropic on Si (001) they elongate dong the step edge direction on misoriented surfaces with a reduction of their lateral size in one direction. AFM measurements are presented which show the wire shaped G e islands on the top of the Si1-xGex (118) template undulation with improve d size homogeneity. The correlation-length of the undulation is mainly cont rolled by the Ge content of the Si1-xGex layer, for example 20 nm large isl ands are grown on the top of Si0.6Ge0.4(118). Low temperature photoluminesc ence spectra are also described which show the evolution of features associ ated with the Si1-xGex template layer for Ge coverage between 1 and 6 ML. D ramatic changes of the photoluminescence spectra were found for a Ge covera ge of 7 ML, the dominant band seen for that coverage is shown to be related to 3D island formation. The influence of the growth conditions an the PL r esults is also discussed. (C) 1998 Elsevier Science S.A. All rights reserve d.