title: Heteroepitaxy of Ge on Si(001) with pits and windows transferred from free-standing porous alumina mask.
abstract: This paper reports the use of ultrathin free-standing porous alumina membrane (PAM) in pattern transferring for selective epitaxial growth (SEG) of Ge dots and films on Si. PAM, as a large-scale, controllable and lithography-free mask, can transfer nanopatterns onto Si without introducing any contaminants. High-density Ge dots are achievable with Ge adatoms confined in Si pits transferred from PAM. High-quality Ge films can also be grown on Si substrates through SiO2 nano-windows. In this work, 80 and 60 nm pore sizes of PAM were transferred to 70, 50 and 20 nm windows for comparison. For the former two sizes, over-etching of Si beneath every SiO2 window forms epi-seeds to improve intermixing of Ge-Si. No threading dislocations can be observed emanating from the epi-seeds due to the decreased lattice mismatch. An innovative shadow-etching technique utilizing the aspect ratio of PAM further decreased the lateral dimension of patterns from 60 to 20 nm. Cross-sectional transmission electron microscopy images show that the selective epitaxial Ge films grown from a 20 nm-width interface are defect free, which is attributed to the exponential decay of strain energy as well as Ge-Si intermixing.
authors.affiliation: State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, People's Republic of China.
authors.forename: Yourui
authors.initials: Y
authors.lastname: Huangfu
authors.forename: Wenbo
authors.initials: W
authors.lastname: Zhan
authors.forename: Xia
authors.initials: X
authors.lastname: Hong
authors.forename: Xu
authors.initials: X
authors.lastname: Fang
authors.forename: Guqiao
authors.initials: G
authors.lastname: Ding
authors.forename: Hui
authors.initials: H
authors.lastname: Ye