325Â nm-laser-excited micro-photoluminescence for strained Si films

Low-temperature micro-photoluminescence (PL) was performed for strained Si (sSi) films by 325 nm-laser excitation at 8.5 K. All of the sSi films were thicker than the penetration depth (dp) of the 325-nm line for Si. The dependence of the PL spectra on the strain condition was studied by comparing dp to the thickness of the strained part (ts), which varied in the sSi film plane. Under the condition ts > dp, the strained-part-related PL (PL-S) was observed, but not the unstrained-part-related PL (PL-US). Under the condition ts < dp, PL-US appeared and its intensity negatively depended on ts, while the intensity of PL-S positively depended on ts. Under the condition of a very small ts, PL-S was never observed. These phenomena were explained by exciton behaviors in sSi film with a band-gap distribution, and enable a deeper understanding of PL characteristics in a relatively large-scale sample with a depth distribution of strain.