Influence of the (111) twinning on the formation of diamond cubic/diamond hexagonal heterostructures in Cu-catalyzed Si nanowires

Abstract

The occurrence of heterostructures of cubic silicon/hexagonal silicon as disks defined along the nanowire ͗111͘ growth direction is reviewed in detail for Si nanowires obtained using Cu as catalyst. Detailed measurements on the structural properties of both semiconductor phases and their interface are presented. We observe that during growth, lamellar twinning on the cubic phase along the ͗111͘ direction is generated. Consecutive presence of twins along the ͗111͘ growth direction was found to be correlated with the origin of the local formation of the hexagonal Si segments along the nanowires, which define quantum wells of hexagonal Si diamond. Finally, we evaluate and comment on the consequences of the twins and wurtzite in the final electronic properties of the wires with the help of the predicted energy band diagram.

Gallium assisted plasma enhanced chemical vapor deposition of silicon nanowires

“…The existence of such twins and even more extended hexagonal regions has been observed in previous works on 111 twinning on Si NWs grown by using Cu as catalyst as well as in III-V nanowires [11,12,34]. The existence of highly periodical and twinned regions leads to the formation of a local hexagonal structure.…”

“…Silicon nanowires are especially interesting as they hold the promise of further electronics miniaturization [8,9]. It has been shown that nanometer sized silicon can crystallize in structures different from the bulk diamond one, with effects on electronic properties [10][11][12]. Moreover silicon nanowires with very small diameters are expected to have a direct band gap [13], which could transform silicon in an efficient optical emitter.…”

Electronic structure and optical properties of Si, Ge and diamond in the lonsdaleite phase

“…This has been attributed to various factors such as the small nanowire radii 10,11 , growth kinetics 12 , interface energies 13 and electron accumulation at the catalyst's interstitial site 14 . It is now believed that the tendency of nanowires to crystalize in WZ/LD phase may be true for group-IV semiconductors as well 15 . It has been experimentally found that Si nanowires with a radius in excess of 10 nm tend to crystalize in the LD phase 16 and a number of recent theoretical investigations have confirmed that the hexagonal LD phase is the more stable for Si nanowires exceeding certain critical dimensions [17][18][19][20] .…”

Inducing imperfections in germanium nanowires

“…Random transverse twin events in Si nanowires have been demonstrated with different non-Au catalysts such as Cu [46], Al [47], Ga [48], AuAg [49], etc. The first demonstration of controlled rational generation of transverse twin boundaries in Au-catalysed Si nanowires was reported by Shin et al [50] Characteristic saw-tooth faceting in nanowire morphology, due to twin boundary formation, was observed in Si nanowires.…”