Low-dimensional SiC nanostructures: Fabrication, luminescence, and electrical properties

Nanocrystalline silicon carbide (SiC) thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (Td) ranging from 80 to 575 °C and different gas flow ratios (GFRs). While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of Td, GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope (HRTEM), micro-Raman, Fourier transform infrared (FTIR) and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300 °C. The degree of crystallization increases with increasing Td and the crystalline fraction (fc) is 65%±2.2% at 575 °C. The fc is the highest for the films deposited with hydrogen d...

Low temperature deposition of nanocrystalline silicon carbide films by plasma enhanced chemical vapor deposition and their structural and optical characterization

A new approach to obtain visible luminescence from sol–gel-derived SiOC films is proposed. In order to investigate the influence of Si and C content, Si- and C-rich SiOC films were prepared as well as stoichiometric SiOC films. High intense white luminescence is obtained where the emission color can be controlled by the experimental parameters such as the starting sol–gel-composition and the pyrolysis temperature. In stoichiometric SiOC films, low pyrolysis temperature yields UV-blue luminescence, whereas high temperatures favor green-yellow luminescence. On the contrary, in Si-rich SiOC films, intense white luminescence is obtained with a broad emission from 430 to 900 nm and an external quantum efficiency (EQE) of 11.5%. Relatively, stoichiometric SiOC films showed an EQE of 5%. Finally, C-rich SiOC films did not show noticeable luminescence due to absorption by carbon clusters.

White Luminescence from Sol–Gel‐Derived SiOC Thin Films

Molecular-dynamics simulations of crystalline (c), nanocrystalline (nc), and amorphous (a) silicon carbides and silicon were carried out to investigate their vibrational and mechanical properties. The atomic configurations, vibrational spectra, and stress-strain curves were calculated at room temperature. In the case of the nanocrystalline structures, these characteristics were analyzed as functions of grain size. Young's and bulk modul and yield and flow stresses were determined from uniaxial deformation of samples under periodic boundary constraints and from experiments on rod extension. For silicon carbides, Young's modulus and flow stress decrease in the sequence ``c-nc-a,'' and with decreasing grain size, which is attributed to a weakening of the Si--C bonds in the amorphous matrix. The enhancement of the strength properties of the homopolar nc--Si structures is attributed to their deformation anisotropy. The calculated vibrational spectra and Young's moduli are in rather good agreement with the corresponding experimental characteristics.

Simulations of the mechanical properties of crystalline, nanocrystalline, and amorphous SiC and Si

Silicon Carbide Nanostructures

Nanocrystalline cubic silicon carbide (3C–SiC) films embedded in an amorphous SiC matrix were fabricated by the hot-filament chemical-vapor-deposition technique using methane and silane as reactance gases. High-resolution transmission electron micrographs clearly showed that these films contain naoncrystallites, with an average dimension of about 7 nm, embedded within an amorphous matrix. X-ray photoelectron spectroscopy, x-ray diffraction, infrared absorption, and Raman scattering studies revealed the nanocrystallites as having the structure of that of 3C–SiC. In contrast to 3C–SiC, where no photoluminescence could be observed at room temperature, strong visible emission with a peak energy of 2.2 eV could be seen from the nanocrystalline films at room temperature. The presence of nanocrystalline cubic SiC in these films is believed to result in a change in their energy-band structure, compared to that of 3C–SiC, which promotes radiative recombination of electron–hole pairs.

J. Cui

Papers

Deposition of nanocrystalline cubic silicon carbide films using the hot-filament chemical-vapor-deposition method