CC BY
1The 30th International Conference on Advanced Laser Technologies LD-I-10
ALT'23
Laser heating of silicon and germanium nanostructures in Raman
studies
A.V. Pavlikov
Faculty of Physics, M.V. Lomonosov Moscow State University, Leninskie Gory, Moscow
119991, Russia
E-mail: [email protected]
The phenomenon of Raman scattering of light is a widespread research technique in which laser radiation is used for excitation. Continuous lasers with relatively low power are used for this purpose. However, when studying objects with a weak Raman scattering signal, in particular micro- and nanostructures, it is necessary to increase the intensity of excitation in order to obtain a recorded response.
Silicon nanostructures demonstrate reversible changes in the Raman spectra under intense laser excitation, which can manifest itself in a shift of peak positions additional to quantum confinement effect [1]. Unlike silicon, germanium has a stronger absorption of visible light; therefore, irreversible changes can occur during laser exposure. These changes lead to the appearance of a nanocrystalline peak in the Raman spectra (Fig.1) [2].
Electrochemically etched porous silicon nanostructures and vertically oriented silicon nanowires exhibit laser heating in two different ways. Porous silicon exhibits a gradual shift in the position of the peak and broadening of the line width. In addition to the manifestation of the heating effect described above, an additional peak can appear in the Raman spectra of vertically oriented silicon nanowires. By decreasing the laser intensity, one can obtain the original spectrum obtained at a low excitation intensity.
A comparison is made of germanium nanowires obtained by electrochemical deposition and ion implantation. Having a similar morphology, these two types of nanostructures also exhibit similar Raman spectra and similar irreversible changes associated with local heating of nanowires to temperatures sufficient for crystallization.
The effects of laser heating can be explained by the low thermal conductivity of nanostructures.
100 200 300 400
Wavenumber, cm"1
Figure 1. Raman spectra of implanted Ge obtained at low (10%) and high (100%) excitation laser intensity.
[1] S. Piscanec, M. Cantoro, A. C. Ferrari, J. A. Zapien, Y. Lifshitz, S. T. Lee, S. Hofmann, and J. Robertson, Raman spectroscopy of silicon nanowires, Phys. Rev. B, vol. 68, pp. 241312- 241316, (2003).
[2] A. M. Sharafutdinova, A. V. Pavlikov, A. M. Rogov, S. N. Bokova-Sirosh, E. D. Obraztsova, A. L. Stepanov, J Raman Spectrosc, vol. 53, p.p. 1055-1061, (2022).
