Dielectric function of nanocrystalline silicon with few nanometers (<3 nm) grain size

Abstract

The dielectric function of nanocrystalline silicon (nc-Si) with crystallite size in the range of 1 to 3 nm has been determined by spectroscopic ellipsometry in the range of 1.5 to 5.5 eV. ATauc-Lorentz parameterization is used to model the nc-Si optical properties. The nc-Si dielectric function can be used to analyze nondestructively nc-Si thin films where nanocrystallites cannot be detected by x-ray diffraction and Raman spectroscopy. During the last few years, nanocrystalline silicon (nc-Si) films have received great attention in photovoltaics 1 and optoelectronics 2,3. Visible photoluminescence (PL) in the range from 770 to 880 nm, depending on crystallite size, has been reported 4 for nc-Si with a grain size in the range from 1 to 3 nm due to a quantum confinement effect, overcoming the impossibility of crystalline silicon (c-Si) to emit light because of its indirect band gap. Nanocrystals of silicon have been demonstrated recently to act as sensitizer for erbium ions (Er31) incorporated in a silicon-based matrix 5 , and to be the most efficient method for obtaining luminescence at 1.54 m. These applications have in common silicon nanocrystallites with a diameter lower than 3 nm. Optimization of devices requires thin-film nanostructure optimization, understanding of the correlation between the nanostructure and optical/electrical properties and, hence, detection of silicon nanocrystallites volume fraction and size distribution. Conventional structural diagnostics, such as Raman spectroscopy and x-ray diffraction (XRD) cannot detect nanocrystallites with a grain size lower than 50 Å 6. High resolution transmission electron microscopy (HRTEM) allows direct detection of very small nanocrystals, but it is destructive and not applicable as a routine analysis. In this letter, spectroscopic ellipsometry (SE) is demonstrated to be useful for nondestructive detection of silicon nanocrystals with a grain size well below 3 nm and for

Large differences in the optical properties of a single layer of Si on Ag(110) compared to silicene

“…If the bands of the ×2 Si layer are not as well defined or if they are not parallel, the interband transitions are expected to be smoothed out. This is the case, for example, for 1-to 3-nm Si nanocrystallites, whose optical response is almost identical to amorphous Si [36]. Finally, the observed energy shift of the main absorption feature with respect to bulk amorphous silicon is likely related to the different environment of the silicon atoms in the SANRs, due to the reduced dimension of the silicon layer and to the presence of the Si-Ag interface.…”

Optical properties of silicon rich oxides

“…In Ref. [5], function 'L', a mixture of 1.5 nm mean radius Si nc's in an aSi matrix was deposited by MS. In Ref.…”

Erbium‐doped nanocrystalline silicon thin films produced by RF sputtering ‐ annealing effect on the Er emission

“…Although samples grown at substrate temperature between 50 ºC and 150 ºC look like amorphous by Raman analysis, the Er34 sample, has been extensively characterized by transmission electron microscopy (TEM) (see ref [5]) shows a volume fraction of 34% of silicon nanocrystallites with a size < 3nm embedded in an a-Si:H matrix. According to the Raman analysis, the as-grown erbium-doped silicon samples produced by RF sputtering can be separated into two groups, namely one group of samples having Si crystal sizes lower than 3 nm (Er34 and P13) and the other group having larger silicon crystals size (P17 and P25 samples).…”