Optical Properties of Multilayered Staggered SiGe Nanodots Depending on Si Spacer Growth Temperature

The optical properties of the multilayered staggered SiGe nanodots (NDs) embedded in the Si spacers fabricated at varying Si growth temperatures are clarified in conjunction with the effect of strain by Photoluminescence (PL) and Raman spectroscopy. We found that compressive strain is induced in the SiGe NDs, with higher growth temperatures of the Si spacer resulting in stronger compressive strain. PL spectra indicate that the higher growth temperature leads to a wider bandgap. This transition energy behavior is caused by not only the strain in the SiGe NDs but also the Ge segregation. Furthermore, luminescence from the SiGe NDs was observed along with luminescence originated at the Si/SiGe interface in the SiGe NDs with a small dot size. This phenomenon was caused by the small energy difference of the conduction-band minima between the SiGe NDs and the tensile-strained Si spacers and the small volume of the tensile-strained Si spacers.