Amplification or cancellation of Fano resonance and quantum confinement induced asymmetries in Raman line-shapes

Abstract

Fano resonance is reported here to be playing a dual role by amplifying or compensating for the quantum confinement effect induced asymmetry in Raman line-shape in silicon (Si) nanowires (NWs) obtained from heavily doped n- and p-type Si wafers respectively. The compensatory nature results in a near symmetric Raman line-shape from heavily doped p-type Si nanowires (NWs) as both the components almost cancel each other. On the other hand, the expected asymmetry, rather with enhancement, has been observed from heavily doped n-type SiNWs. Such a system (p- & n-) dependent Raman line-shape study has been carried out by theoretical line-shape analysis followed by experimental validation through suitably designed experiments. A dual role of Fano resonance in n- and p-type nano systems has been observed to modulate Raman spectra differently and reconcile accordingly to enhance and cease the Raman spectral asymmetry respectively. The present analysis will enable one to be more careful while analyzing a symmetric Raman line-shape from semiconductor nanostructures.

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.…”

Brain Tumour Detection and Grading Using Raman Scattering: Analogy from Semiconductors for Solving Biological Problem

“…Raman line-shape analysis has been done from a very well-known semiconductor system, Si, where quantum confinement effect and electron-phonon (Fano) interaction have been used as known control perturbations and will be discussed one-by-one for validation. For this purpose, the theoretical Raman line shapes have been generated using the universal perturbation dependent Raman line-shape function developed earlier by Richter et al [43] and later modified by Campbell et al [44,45] and several others [5,6,10,15,[46][47][48][49][50]. The simplified general equation for universal Raman line shape can be represented by Eq.…”

“…Mode identification can be done by indexing the Raman peak positions but it may contain lot more information than simple chemical bonds energies which may also be investigated using IR spectroscopy, of course with certain limitations. Beyond the peak position of a Raman peak, the overall line shape of the spectrum is equally important as it may reveal several important physical phenomena taking place at microscopic level like quantum confinement or size effect, electron-phonon effect, fantum effect etc [9][10][11][12][13][14][15][16][17]. Apart from direct evidences, as a consequence of Raman line-shape's sensitivity towards external conditions, perturbations induced by temperature, pressure etc also can be investigated using classical and advanced Raman techniques [18][19][20][21][22].…”

Expressing Raman Spectral Details Through Raman Parameter Information Diagram (RAPID)

“…The peak can change in terms of a shift in its peak position (red-or blue-shift), its spectral width (characterized by FWHM), its symmetry, presence of antiresonance etc. [12][13][14][15] . All such changes provide information about, pressure, stress (or strain), quantum confinement effect, Fano resonance, heating etc [16].…”