Deviations from ideal nucleation-limited relaxation in high-Ge content compositionally graded SiGe∕Si

The authors report the sudden rise in threading dislocation density in Ge-rich relaxed graded SiGe layers grown at higher growth temperatures $(T>550°\mathrm{C})$ . They attribute this rise in threading dislocation density in relaxed Ge to dislocation nucleation. This observation is contrary to conventional graded buffers in Si-rich material, where higher growth temperatures result in reduced threading dislocation densities (TDDs). Additionally, a coupling effect between the effective strain during graded buffer growth and the growth rate was observed, as evidenced by increased TDD values at reduced growth rates. They conclude that reduced growth rates allow more time for the surface to evolve (i.e., roughen) during growth, thereby trapping mobile dislocations and necessitating the nucleation of additional dislocations to continue relaxing the structure.