Investigation of dislocations in composition graded and strain relaxed SiGe epitaxial layer by cathodeluminescence

Dislocations in stair-like composition graded SiGe layer and relaxed SiGe layer with Ge composition of 15%, 20% and 20% have been investigated with chemical etching and cathodeluminescence (CL). Etch pit density in the s-Si region is contained with the order of 104 cm−2 and it is almost constant in the relaxed and graded SiGe layer with the order of 105 cm−2 for every Ge composition samples. From the observation of the cleaved surface, misfit dislocations pile up at the boundary in each layer and Ge composition changing regions. Defect relative luminescence lines (D1 and D2 lines) were observed, but D3 and D4 lines were not present in the present samples. It is found that the luminescence intensity ratio of D1 to D2 depends on acceleration voltage of CL. From these results, it is suggested that the amount ratio of dislocation type causing D1 and D2 changes with the depth from surface.