Formation of flat, relaxed Si1−xGex alloys on Si(001) without buffer layers

Abstract

Atomically flat, fully strained Si 1−x Ge x layers with thicknesses ranging from 40 to 240 nm were grown on Si͑001͒ at 450°C by ultrahigh-vacuum chemical vapor deposition and subjected to annealing at 1000°C for 20 min to induce relaxation. In order to minimize surface diffusion during annealing and thereby inhibit strain-induced roughening in favor of misfit dislocation formation, SiO 2 capping layers are deposited prior to annealing. The overall process results in smooth, relaxed alloy layers without the necessity of using several-m-thick compositionally graded buffer layers.

Thermal annealing effects on a compositionally graded SiGe layer fabricated by oxidizing a strained SiGe layer

“…The small variation of the rms indicates that the strain relaxation due to surface roughening is prevented during the thermal annealing. Certainly, the top SiO 2 layer formed by oxidizing Si cap layer at the very beginning should be beneficial to the flat surface, as reported in reference [20]. Fig.…”

Strain relaxation in SiGe layer during wet oxidation process

“…It is worth noting that there are oxide layers on the SiGe layers for the oxidation samples. These oxide layers may inhibit surface diffusion during wet oxidation at early stage, thus transforming the strain relaxation mechanism from strain-induced surface roughening to dislocation formation [20]. However, with increase of oxidation time, the residual strain cannot be relieved by generation or propagation of dislocations.…”

Fabrication of strained Ge film using a thin SiGe virtual substrate

“…Figure 5(a) is a high resolution XTEM image of the SiGe/Si substrate interface. Due to the large lattice mismatch between the Si substrate and the SiGe layer, a lot of dislocations nucleate at the interface and extend into the SiGe layer which having an angle of 60 • with the interface [15] . Figure 5(b) is an XTEM image of the whole epitaxial layer including the Si cap/Ge/SiGe/Si substrate.…”