Relaxation of strained silicon on Si0.5Ge0.5 virtual substrates

Abstract

Strain relaxation has been studied in tensile strained silicon layers grown on Si 0.5 Ge 0.5 virtual substrates, for layers many times the critical thickness, using high resolution x-ray diffraction. Layers up to 30 nm thick were found to relax less than 2% by the glide of preexisting 60°d islocations. Relaxation is limited because many of these dislocations dissociate into extended stacking faults that impede the dislocation glide. For thicker layers, nucleated microtwins were observed, which significantly increased relaxation to 14%. All these tensile strained layers are found to be much more stable than layers with comparable compressive strain.

Highly strained Si epilayers grown on SiGe/Si(100) virtual substrate by reduced pressure chemical vapour deposition

“…Etching of strained Si layers revealed presence of SFs also observed by XTEM. Figure 4 [3]. There is a certain range of Si layer thickness, which depends on lattice mismatch strain, where SFs density gradually increases with increasing layer's thickness up to a sufficient enough density resulting in a few percents of strain relaxation that could be measured by HR-XRD or easy observed by XTEM, but we do not observe this density in any of analyzed layers.…”

“…In contrast to the widely used dichlorosilane (SiH 2 Cl 2 ) and silane (SiH 4 ) precursors for epitaxial growth of s-Si epilayers by RP-CVD we employed the relatively new high purity disilane (Si 2 H 6 ) gas precursor [3][4][5][6][7]. Comparing to the previously mentioned gases it allows higher growth rates to be achieved at the same growth conditions and potentially enables lowertemperature epitaxial growth regimes to be explored.…”

“…This is well above the equilibrium critical thickness of s-Si on a relaxed Si 0.5 Ge 0.5 /Si(100) VS of around 5nm. Strain relaxation has to be avoided because high density of defects formed can suppress the enhanced carrier mobility [2,3].…”

Introduction of Terraces into a Reverse Linearly Graded SiGe Buffer on Si(001) Substrate and Their Effect on the Buffer's Structural Properties

“…Figure 7 shows the measured etch rates for the truncated terraces grown. The Schimmel etch rate was previously found 21 to decrease approximately logarithmically as the Ge composition increased from 20% to 80%, becoming undeterminable above 80% due to the small etch rate. The iodine etchant also shows a logarithmic decrease in etch rate as the Ge composition increases from 78.8 % to 100 % and is at least two orders of magnitude larger than for the Schimmel etchant over the entire range.…”

“…In low (x < 0.5) content Si 1−x Ge x layers Schimmel etchant has been the standard selective etchant for many years; 20 however, as the Ge composition increases the reactivity of this etchant decreases and it has no effect on pure Ge. 21 An Iodine based etchant has been shown to be effective at revealing defects in pure Ge, 22 CH 3 COOH in the volume ratio 5:10:11 with 30 mg iodine dissolved per 26 mL solution, 24 this mixture was then further diluted with DI water in the ratio 3:1. Figure 7 shows the measured etch rates for the truncated terraces grown.…”