The Nucleation and Propagation of Misfit Dislocations aear the Critical Thickness in Ge-Si Strained Epilayers

Abstract

The nucleation and propagation of misfit dislocations in Ge-Si strained epilayers on (100) Si have been investigated using transmission electron microscopy and X-ray diffraction topography at low lattice parameter mismatch (˜ 0.8%). Misfit dislocations nucleate as half loops which are predominantly unfaulted (> 90%) at the advancing growth interface. Under the driving force of the epilayer strain, unfaulted half loops glide and expand on inclined { 111 }planes toward the heterointerface (i.e. substrate/epilayer interface). These unfaulted half loops consist of a 60°-dislocation segment which lies along < 011> in a plane parallel to the heterointerface (i.e. (100)) and this segment is connected to the growth interface by two screw dislocation segments which both lie on the same inclined {111} glide plane. As 60° dislocations reach the heterointerface on each of the four inclined {111} variants, they form an orthogonal array of misfit dislocations which lie along [011] and [011]. At higher lattice parameter mismatch (˜ 2%), there appear to be some important changes in the dislocation behavior and these changes result in orthogonal arrays of heterointerface dislocations which are predominantly edge type (i.e. 90°dislocations).

Structure, properties and applications of GexSi1-xstrained layers and superlattices

“…Another very sensitive tool to measure small concentrations of dislocations is the electron beam induced current (EBIC) technique used by Kohama et al (1987Kohama et al ( , 1988; their results are shown in figure 3 for dislocations at a Ge,Si, -JSi interface. These results are similar to those of Eaglesham et al(1988) obtained by x-ray topography, in that for small Ge concentrations the observed values of h, are considerably smaller than the values given by Bean (1985, 1986a) and appear to support the suggestion made by Fritz (1987) that the sensitivity of the measuring technique is important in determining the correct value of h, (see section 2.3).…”

“…Bean et al (1984) examined the crystalline quality of MBE grown Ge,Si, _ x strained layers by Rutherford back scattering and ion channelling methods and showed that with growth rates of about 5 A sC1 both good morphology and good crystalline quality can be obtained if the growth temperature is in the neighbourhood of 550 "C. (1988) and Kvam et al (1988) studied the generation of dislocations at the Ge,Si,_,/Si interface by using the x-ray topography technique and found that h, for an epilayer containing 13 % Ge was 180 nm. This value is about a factor of four smaller than the experimental value obtained by Beanet al (1984) (see figure 1) but about 2.5 times as large as van de Merwe's value 70 nm (based on equilibrium theory, see equation (2.10)) for this composition.…”

“…This value is about a factor of four smaller than the experimental value obtained by Beanet al (1984) (see figure 1) but about 2.5 times as large as van de Merwe's value 70 nm (based on equilibrium theory, see equation (2.10)) for this composition. Eaglesham et al (1988) showed that the discrepancy between the value of 180 nm and the equilibrium value of 70nm can be explained by taking into account the fact that even x-ray topography has limited sensitivity and can not detect dislocations which are smaller than 20 pm. Another very sensitive tool to measure small concentrations of dislocations is the electron beam induced current (EBIC) technique used by Kohama et al (1987Kohama et al ( , 1988; their results are shown in figure 3 for dislocations at a Ge,Si, -JSi interface.…”

SiGe nanostructures: new insights into growth processes

“…Various mechanisms have been proposed to explain the surface cross-hatch formation. Because of the lattice mismatch between the layer and the substrate, dislocations are introduced in the layer at the growth front [21,22] and propagate to the epilayer/substrate interface where misfit segments are formed whose edge component relieves the strain accumulated in the layer. Due to the low strain inside the layer, it is favourable for the two threading dislocations associated with the misfit segment to glide in order to increase the misfit segment length rather than nucleate new dislocations.…”