Raman study of phase transformation from diamond structure to wurtzite structure in the silicon nanowires

Crystalline, Phononic, and Electronic Properties of Heterostructured Polytypic Ge Nanowires by Raman Spectroscopy

“…When semiconductors are grown in the form of nanowires (NWs), they can exist in different crystal structures: this exciting phenomenon is known as polytypism . NWs also allow for the existence of crystal phases that do not even exist in the bulk counterpart. , Besides non-nitride III–V materials, Si − and Ge − in the NW form can exist in the hexagonal 2H phase (properly named as lonsdaleite), which in the bulk is hardly obtained (usually under high pressure conditions). , …”

“…1 NWs also allow for the existence of crystal phases that do not even exist in the bulk counterpart. 2,3 Besides non-nitride III-V materials, Si 4,5,6,7,8,9 and Ge 10,11,12 in the NW form can exist in the hexagonal 2H phase (properly named as lonsdaleite), which in the bulk is hardly obtained (usually under high pressure conditions). 13,14 The formation of NWs with hexagonal crystal symmetry has attracted enormous interest among researchers.…”

A Review on Metastable Silicon Allotropes

“…Although Raman scattering is one of the most effective methods for detecting Si( hP 4), the precise peak position was slightly shifted in different reports. In Shukla’s experiment, Raman active optical modes of Si( hP 4) were around 515 cm −1 , 507 cm −1 , and 495 cm −1 , respectively [ 23 ]. Rodichkina and Lysenko [ 24 ] reported a reversible photo-induced formation of Si( hP 4) in initially metal-assisted chemical etching-fabricated diamond cubic Si nanowires, but they observed the Raman peaks centered near 490 cm −1 , 510 cm −1 , and 517 cm −1 , corresponding to the Si( hP 4) phase in their experiment.…”

“…Rodichkina and Lysenko [ 24 ] reported a reversible photo-induced formation of Si( hP 4) in initially metal-assisted chemical etching-fabricated diamond cubic Si nanowires, but they observed the Raman peaks centered near 490 cm −1 , 510 cm −1 , and 517 cm −1 , corresponding to the Si( hP 4) phase in their experiment. Theoretical and experimental studies suggest that the Si( hP 4) indirect band gap is in the near-infrared range, near the emission of erbium in bulk silicon [ 6 , 23 ], while a direct transition at point Γ is at around 1.4–1.6 eV [ 37 , 38 , 39 , 40 ] (see in Table 2 ) and the emission efficiency is 2–3 orders of magnitude greater than that of Si( cF 8) in the visible-light region. Surprisingly, Si( hP 4) is transformed into a direct band gap semiconductor under strain (>4%) [ 40 ] or germanium doping [ 41 ], and its band gap width shows good tunability for different strain and compositions; hence, it may open a new scenario in the field of silicon-based rare-earth-free optoelectronic devices.…”

“…Such silicon can also be used as antireflecting material due to its high absorption coefficient in the visible/near infrared region and special morphology. Shukla [ 23 ] determined an optimal deposition time of 20 s and etching time 30 min, and they believed that the difference in surface energy between hydrogenated silicon and silicon was the essence for the induced silicon phase transition.…”