Structure, optical property, and reaction process of Si quantum dots embedded in an amorphous silicon carbide matrix

Abstract

Silicon quantum dots (QDs) embedded in an amorphous silicon carbide matrix were prepared using silane, methane, and hydrogen as reactive gases at a low substrate temperature by radio-frequency plasma enhanced chemical vapor deposition followed by thermal annealing at 1000 °C in a N2 atmosphere in the quartz furnace. The structure, optical properties, and reaction process of the synthesized Si QDs embedded in an amorphous silicon carbide matrix under different discharge powers are investigated. With the increase in the discharge power from 40 to 100 W, the experimental result measured by X-ray diffraction, Raman spectroscopy, UV-Visible spectroscopy, and field emission scanning electron microscopy reveals that the average size and the crystal volume fraction of Si QDs decrease from 4.4 to 3.4 nm and from 61.1% to 46.3%, respectively, while the optical bandgap and the deposition rate increase from 1.75 to 1.96 eV and from 15.5 to 16.5 nm/min, respectively. Moreover, the real-time diagnosis of plasma by optical emission spectroscopy (OES) is used to determine the chemical species and excitation temperature under the glow discharge of silane, methane, and hydrogen gas mixtures. Based on the OES measurement, the chemical reactions happening in the plasma and growth mechanism for the synthesis of Si QDs embedded in an amorphous silicon carbide matrix have been proposed. This work plays a significant role in preparation of the Si QDs embedded in an amorphous silicon carbide matrix for third-generation photovoltaic solar cells.