Experimental Study of Silicon Monolayers for Future Extremely Thin Silicon-on-Insulator Devices: Phonon/Band Structures Modulation Due to Quantum Confinement Effects

We have experimentally studied Si monolayers, fabricated by thermal oxidation of silicon-on-insulator (SOI) substrates at high temperature, for future extremely thin SOI (ETSOI) complementary metal oxide semiconductor (CMOS) devices, and have shown the strong quantum confinement effects in the ETSOIs. We have successfully formed 0.52-nm Si monolayers, as confirmed by transmission electron microscopy (TEM) and a UV/visual reflection method. We have experimentally shown the asymmetric broadening and the peak downshift of the Raman peak of ETSOIs evaluated by UV-Raman spectroscopy, which is enhanced in the ETSOI thickness $T_{\text{SOI}}$ of less than about 5 nm. These results are due to the quantum phonon confinement effects in ETSOIs. Using the TEM observation and UV-Raman spectroscopy of ETSOIs, we have also shown the tensile strain of ETSOIs due to the Si bending and the $T_{\text{SOI}}$ variations in ETSOI substrates. In addition, we have observed photoluminescence (PL) from the ETSOIs with a $T_{\text{SOI}}$ of less than about 5 nm and the PL intensity strongly depends on the $T_{\text{SOI}}$. However, the peak photon energy of about 1.85 eV in the PL spectrum is independent of the $T_{\text{SOI}}$. We cannot explain the PL results perfectly at present, but we have introduced a possible three-region model of electron/hole pair generation in a two-dimensional Si layer and electron/hole pair recombination at the Si/SiO 2 interface state region.