Impact of SiGe layer thickness in starting substrates on strained Ge-on-insulator pMOSFETs fabricated by Ge condensation method

We study the impact of the SiGe thickness in starting substrates composed of Si/Si_0.25Ge_0.75/SOI(100) structures for the Ge condensation process on the resulting Ge-on-insulator (GOI) film properties. We evaluate the physical properties of the GOI films using AFM and Raman spectroscopy. It is found that 10-nm-thick GOI films with higher compressive strain (ε_c = 1.75%) and more uniform spatial strain distribution are obtained for 40 nm-thick-Si_0.75Ge_0.25 through a Ge condensation process with slow cooling than 60 nm-thick-SiGe. This suppression of strain relaxation is due to the lower total strain energy by the thinner SiGe layer. By using this GOI substrate, 10-nm-thick GOI p-channel metal-oxide-semiconductor field effect transistors (pMOSFETs) are demonstrated with the high performance of μ_h = 467 cm² V⁻¹ s⁻¹ and I_on/I_off > 7.2 × 10⁵. The effective hole mobility of the 10 nm-thick GOI pMOSFET increases significantly with reducing measurement temperature from 298 K to 100 K, indicating the high contribution of phonon scattering to the mobility.