Influence of freely diffusing excitons on the photoluminescence spectrum of Si thick films with depth distribution of strain

We present an interpretation of photoluminescence (PL) for relatively thick Si films (200-300 nm) with depth distribution of strain, in which freely diffusing excitons influence the PL signal that originates from layers with different strain conditions. Micro-PL was excited by a 325 nm laser at 8.5 K for the Si films. The PL spectra clearly depended on the thickness of the strained part (t_s) in the strained Si film. Under the condition of t _s greater than the penetration depth (d_p) of 325 nm line for Si, only the strained-part-related PL(PL_s) could be observed but not the unstrained-part-related PL(PL_us). With a decrease in t _s, PL_us gradually appeared and became strong, and simultaneously PL_s became weak. For positions with very small t _s, PL_s could never be observed. The strain completion for the Si films was also investigated based on exciton behaviors in strained semiconductor. These characteristics of PL are useful references for understanding exciton behavior in semiconductor with depth distribution of band gap.