325 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 (d_p) of the 325-nm line for Si. The dependence of the PL spectra on the strain condition was studied by comparing d_p to the thickness of the strained part (t_s), which varied in the sSi film plane. Under the condition t_s > d_p, the strained-part-related PL (PL-S) was observed, but not the unstrained-part-related PL (PL-US). Under the condition t_s < d_p, PL-US appeared and its intensity negatively depended on t_s, while the intensity of PL-S positively depended on t_s. Under the condition of a very small t_s, 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.