Dislocation-related photoluminescence peak shift due to atomic interdiffusion in SiGe/Si

Low-temperature photoluminescence (PL) spectroscopy was used to study electronic states associated with threading dislocations (D lines) in strain-relaxed ${\mathrm{Si}}_{\text{1−x}}{\mathrm{Ge}}_x$ layers. The structures investigated were grown by ultrahigh vacuum chemical vapor deposition at 550 °C and consist of a Si(001) substrate, followed by a stepwise graded buffer layer, followed by a thick uniform composition ${\mathrm{Si}}_{\text{1−x}}{\mathrm{Ge}}_x$ layer. The PL peak positions of the four D lines after isochronal annealing at temperatures between 600 and 800 °C were measured. We show that the large energy shift of the $\text{D1}$ line is due to a change in the local band gap energy at the dislocation core due to strain-driven diffusion of Ge atoms away from the dislocation core with an activation energy $E_a,$ which varies with Ge mole fraction x.