Carrier gas effects on the SiGe quantum dots formation

SiGe quantum dots (QDs) grown by ultra-high vacuum chemical vapor deposition using H2 and He carrier gases are investigated and compared. SiGe QDs using He carrier gas have smaller dot size with a better uniformity in terms of dot height and dot base as compared to the H2 carrier gas. There is a higher Ge composition and less compressive strain in the SiGe QDs grown in He than in H2 as measured by Raman spectroscopy. The Ge content is higher for He growth than H2 growth due to hydrogen induced Si segregation and the lower interdiffusivity caused by the more strain relaxation in the He-grown SiGe dots. The photoluminescence also confirms more compressive strain for H2 growth than He growth. Hydrogen passivation and Ge-H cluster formation play an important role in the QDs growth.