Strain relaxation during solid-phase epitaxial crystallisation of Ge_xSi_1-x alloy layers with depth dependent Ge compositions

Solid-phase epitaxial growth (SPEG) of amorphous GeSi alloy layers has been examined. It is shown that fully strained depth dependent GeSi alloy layers can be produced by multiple ion-implantation and SPEG for implant doses below critical values. For doses above these critical values strain relaxation is shown to occur during SPEG at a well defined depth, and to be correlated with a reduction in the SPEG velocity caused by roughening or faceting of the crystalline/amorphous interface. The velocity reduction is shown to be a reliable indicator of strain relaxation. Both the critical dose and the depth at which strain relaxation occurs are shown to be in excellent agreement with equilibrium critical thickness theory.