Local strain evaluation for freestanding Si membranes by microphotoluminescence using UV laser excitation

UV laser excited microphotoluminescence (PL) was used to evaluate the local strain for freestanding Si membranes (FSSMs), which can be applied to the fabrication of high performance radiofrequency (RF) power amplifier. The FSSMs were fabricated by the mesa etching of Si on insulator followed by etching of the buried oxide. Compressive strain in the membranes was induced by SiN deposition using low-pressure chemical vapor deposition. By the optimization of optics, we successfully observed PLs for FSSMs by a 325 nm laser excitation, which eliminated the substrate-related PL (S-PL) and improved the accuracy of the identification for PL peaks. Strain-induced band gap narrowing was directly observed by identifying the PL peak of the free exciton band-band transition in membranes, from which the strain ratio was estimated for each sample. Strain was reasonably dependent on the sample parameters, which implies that this measurement gives valid results. Based on the improved accuracy of PL peak identification by a UV laser excitation, a minor revision of the strain ratio results was also performed for our previous report for the same samples, which were measured by a 514 nm laser excited PL.