Heterostructures GexSi1-x/Si(001) (x=0.18-0.62) grown by molecular beam epitaxy at a low (350 °C) temperature:: specific features of plastic relaxation

The specific features of plastic relaxation of GexSi1-x/Si(001) (x=0.18-0.62) heterostructures grown by molecular beam epitaxy at a low (350-400 degreesC) temperature with the use of a low-temperature buffer Si layer are considered. In the range of compositions up to x=0.3, GexSi(1-x)/Si(001) films can be grown with a density of threading dislocations (i.e. threading segments of 60degrees mismatch dislocations) lower than 10(6) cm(-2). It is concluded that the basic influence of the low temperature of epitaxy on the decrease in threading dislocation density is manifested in: (i) lower rate of dislocation nucleation; and (ii) greater mean threading dislocations slip velocity. One can assume that the reason for the increase in threading dislocation density in GexSi1-x films with a high (xgreater than or equal to0.3) content of Ge is the origination of an additional and powerful source of misfit dislocations: facilitated nucleation of these dislocations from the surface. It is shown that the density of threading dislocations in heterostructures only increases with increasing plastic relaxation of the latter. This makes the significance of the contribution of dislocation annihilation to the decrease in the final threading dislocations density with the use of the low-temperature buffer layer doubtful. (C) 2004 Elsevier B.V. All rights reserved.