Photoluminescence characterization of strained Si-SiGe-on-insulator wafers

Photoluminescence (PL) was observed for three strained Si-SiGe-on-insulator wafers with different Ge fractions, which were fabricated using Ge condensation by the dry oxidation of SiGe on a silicon-on-insulator substrate. PL signals were excited by an Ar⁺ laser operated at 514 nm and a HeCd laser operated at 325 nm. The PL signal excited by the 325 nm line was confirmed to emit only from layers on buried oxide. Under 325 nm line excitation, the PL signals of wafers with 13 and 18% Ge fractions are deep-level-free in the PL energy range from 0.77 eV to the band gap, implying high wafer qualities. However, a broad PL signal could be observed for a wafer with a 25% Ge fraction, which was confirmed to be defect-related by varying laser power. Integrated band-band PL signal intensity decreased with increasing Ge fraction, implying a wafer quality dependence on Ge fraction. The dependence of the PL signal intensity on Ge fraction was discussed in detail.