Challenges in epitaxial growth of SiGe buffers on Si (111), (110), and (112)

The growth of SiGe on surfaces other than Si(001) is of interest in VLSI technology both for realizing novel, high-mobility channels and for use in epitaxial source/drains. In this paper we report that thick, low-mismatch SiGe films grown on Si(111), (110), and (112) possess threading dislocation densities (TDD) > 10 × higher than comparable films on (001). We further show that one of the primary factors limiting crystalline quality on Si(111), (110), and (112) is the tendency towards stacking fault and microtwin formation which result from the nucleation and glide of dissociated Shockley partial dislocations. These microtwins are believed to arrest the propagation of strain-relieving misfit dislocations, necessitating further nucleation events and an overall rise in TDD. Therefore, while low-TDD SiGe buffers on Si (001) can typically be graded at 10–20% Ge/μm, it appears that attainment of similar TDDs on (111), (110), or (112) may require substantially lower grading rates and correspondingly thicker films.