Quantum-confined direct-gap transitions in tensile-strained Ge/SiGe multiple quantum wells

Tensile-strained Ge/Si(1-x)Ge(x) (x = 0.87) multiple quantum wells (MQWs) on a Ge-on-Si virtual substrate are investigated with Brewster transmission and photo-reflectance, to identify quantum-confined direct-gap transitions and their light/heavy-hole splitting. Strain is deduced from optical splitting and x-ray diffraction measurements. As-prepared MQWs have an exciton at approximate to 820 meV, close to the 810 meV edge of the telecommunication C-band. The effect of rapid thermal annealing, to red-shift this feature into the C-band via increased strain, is investigated and interpreted with a tight-binding model. Annealing is observed to red-shift bulk absorption, but MQW transitions experience a net blue-shift due to interdiffusion. (C) 2011 American Institute of Physics. [doi:10.1063/1.3606383]