Growth of high-quality SiGe films with a buffer layer containing Ge quantum dots

High-quality SiGe films with a buffer layer containing Ge quantum dots have been grown by ultra-high vacuum chemical vapor deposition. For Ge dots/Si bilayers up to 10 periods, threading dislocation density and the residual strain in the SiGe uniform epilayers were found to reduce drastically with the increasing period. The Si_0.8Ge_0.2 film grown on a 10-period Ge dots/Si bilayers was demonstrated to have a threading dislocation density of 2.0 × 10⁵ cm^{- 2} with a residual strain of only 11%. Strained-Si n-channel metal-oxide-semiconductor transistors with various buffer layers were fabricated and examined. Effective electron mobility for the strained-Si device with the multiple Ge quantum dots buffer layer was found to be 90% higher than that of Si control device. The scheme for the formation of the relaxed SiGe film serving as a virtual substrate shall be applicable to high-speed strained-Si devices.