Spectral Anomaly in Raman Scattering from p-Type Silicon Nanowires

Abstract

An anomalous nature of Raman spectral asymmetry has been reported here from silicon nanowires (SiNWs) prepared from a heavily doped p-type Si wafer using a metal induced etching technique. Raman spectra of SiNWs prepared from two p-type Si wafers with different doping levels show different behaviors in terms of asymmetry as characterized by the asymmetry ratio. The SiNWs prepared from high doped p-type wafer show an anomaly in asymmetry in addition to the red shift and broadening of the Raman line shape due to the presence of the “FAno-quaNTUM” (FANTUM) effect. The heavy doping in the wafer provides a continuum of energy states to be available to interact with confined optic phonons which results in electron–phonon interaction. SiNWs prepared from low doped p-type wafer show a red shift and asymmetric broadening due to the quantum confinement effect alone. Careful analysis has been provided to clearly understand the role of Fano and quantum effects in p-type SiNWs with high doping and their relative contribution in Raman line-shape half-widths. A theoretical framework for supporting the presence of the FANTUM effect has also been proposed to show that how a system with appropriate Fano and quantum effects’ relative contribution may result in a near-symmetric Raman line shape.

Effect of annealing temperature on thermo‐diffusional boron doping of silicon nanowire arrays probed by Raman spectroscopy

“…MACE formation of SiNW arrays on highly boron‐doped c‐Si substrates leads to the narrowing of nanowire diameter and additional nanowire porosity that results in a distortion of the lower wavenumber side of Fano‐resonance line. [ 32,33,35,36 ] Note that in this case, the observed distortions in Raman spectra correspond to theoretical considerations that phonon confinement reveals itself in the structures with a diameter less that 10–20 nm. [ 23–29,31–34 ] We do not observe any maximum red shift within the chosen spectral resolution or a broader half‐width at the lower wavenumber side of the Raman spectra of as‐prepared and thermally annealed SiNWs (Figure 2a) as could be expected for small‐diameter nanowires.…”

“…Because the Raman line shape can be modified by phonon confinement, [ 22–36 ] one should be scrupulous about the possible impact of phonon confinement to the estimations of the FCC concentration in SiNWs. MACE formation of SiNW arrays on highly boron‐doped c‐Si substrates leads to the narrowing of nanowire diameter and additional nanowire porosity that results in a distortion of the lower wavenumber side of Fano‐resonance line.…”

Oxygen and cerium defects mediated changes in structural, optical and photoluminescence properties of Ni substituted CeO2

“…In defect-free crystalline semiconductor (bulk) materials one expects perfect symmetry. Asymmetry increases with decreasing crystallite size and is most prominent when size is smaller than Bohr excitation radius ~7.2nm of CeO2 [28,30,31]. Since with reduction of size and dimension an increasing volume of reciprocal space is involved which leads to participation of phonons of other than zone boundary [28].…”

Generalisation of phonon confinement model for interpretation of Raman line-shape from nano-silicon

“…Besides certain disadvantages, the PCM has been used as the most widely used formulation when it comes to interpretation of the Raman scattering results obtained from low dimensional semiconductors especially elemental ones. In recent attempts to rectify the shortcomings of the PCM, Jia et al [21] have been reported in the previous literature [22][23][24]. In order to confirms the wire like structures formed after etching, transmission electron microscopy (TEM) was carried out using TEM-Gatan model 636MA.…”

“…For comparison, Raman line-shape obtained using well-established PCM[13,16,17,23,30], as represented Raman line-shapes theoretically generated using phonon confinement model Eq. 2 for different SiNSs.…”