Influence of germanium content on the photoluminescence of erbium- and oxygen-doped SiGe grown by molecular beam epitaxy

The photoluminescence at 1.54 μm of erbium- and oxygen-doped Si/Si1−xGex samples grown completely by molecular beam epitaxy has been investigated for germanium concentrations ranging from x=0 to x=0.165. The dopants were either placed into the Si1−xGex or into the Si layers of an alternating Si/Si1−xGex layer structure. Because of the good crystal quality after growth, it was possible to obtain all luminescence data from as-grown samples without annealing. We observed a decrease in photoluminescence (PL) intensity and a stronger temperature dependence with increasing Ge content. For samples with the same Si/Si1−xGex layer structure, an enhancement of PL intensity at low temperature was seen when erbium and oxygen were placed into the Si1−xGex layers rather than into the Si layers. We attribute this effect to a capture of photogenerated carriers in the Si1−xGex layers.