High-frequency conductivity of optically excited charge carriers in hydrogenated nanocrystalline silicon investigated by spectroscopic femtosecond pump-probe reflectivity measurements

THIN SOLID FILMS

卷:592

Article; Proceedings Paper

He, Wei¹  Yurkevich, Igor V.²  Zakar, Ammar¹  Kaplan, Andrey¹ 

[1] Univ Birmingham, Sch Phys & Astron, Birmingham B15 2TT, W Midlands, England

[2] Aston Univ, Nonlinear & Complex Res Grp, Birmingham B4 7ET, W Midlands, England

关键词: Nanomaterials;    High-frequency conductivity;    Nanosilicon;    Ultrafast spectroscopy;   

DOI  :  10.1016/j.tsf.2015.03.023

来源: Elsevier

【 摘 要 】

We report an investigation into the high-frequency conductivity of optically excited charge carriers far from equilibrium with the lattice. The investigated samples consist of hydrogenated nanocrystalline silicon films grown on a thin film of silicon oxide on top of a silicon substrate. For the investigation, we used an optical femtosecond pump-probe setup to measure the reflectance change of a probe beam. The pump beam ranged between 580 and 820 nm, whereas the probe wavelength spanned 770 to 810 nm. The pump fluence was fixed at 0.6mJ/cm(2). We show that at a fixed delay time of 300 fs, the conductivity of the excited electron-hole plasma is described well by a classical conductivity model of a hot charge carrier gas found at Maxwell-Boltzmann distribution, while Fermi-Dirac statics is not suitable. This is corroborated by values retrieved from pump-probe reflectance measurements of the conductivity and its dependence on the excitation wavelength and carrier temperature. The conductivity decreases monotonically as a function of the excitation wavelength, as expected for a nondegenerate charge carrier gas. (C) 2015 Elsevier B.V. All rights reserved.

【 授权许可】

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