Structural and optical properties of silicon carbide quantum dots grown by very high frequency plasma enhanced chemical vapour deposition

Abstract

This study presents the synthesis of Silicon Carbide Quantum Dots (SiC QDs) by Very High Frequency-Plasma Enhanced Chemical Vapour Deposition (VHF-PECVD) method. Si (100) was used as a substrate where the growth was performed at a much lower temperature (100°C) than previous work. Besides, the growth time has been shorten in order to enhance the SiC QDs growth process. The effect of different Radio Frequency (RF) plasma frequencies (150 MHz, 160 MHz and 200 MHz) on the structural properties of SiC QDs were investigated. The growth parameters such as growth temperatures, growth time and hydrogen flow rates were manipulated in order to study the optical properties of SiC QDs grown at 150 MHz. Silane (SiH4) and methane (CH4) were used as precursor gases and both were decomposed by RF plasma excitation to silicon (Si) and carbon (C) respectively at certain temperature for the growth of SiC QDs. The samples were then characterized by Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Microscopy (EDX) and Atomic Force Microscopy (AFM) to observe the morphology and structure of quantum dots. FESEM images show that the dots diameter increased as the RF plasma increased from 150 MHz to 200 MHz and the EDX analysis further confirmed that quantum dots consist mostly of silicon (Si), carbon (C) and oxygen (O) elements. From the cross-sectional image, it was suggested that the growth of SiC quantum dots follows Stranski-Krastanow (S-K) mode. Moreover, AFM results revealed that the surface roughness also increased concurrently with the increased of RF plasma frequencies. Raman spectra analysis and X-Ray Diffraction (XRD) pattern further confirmed that some of them composed of crystalline peak of SiC at 780.32 cm-1 with (200) growth plane. For emission properties of SiC QDs, two peaks detected for all samples located at 407 nm and 571 nm which are comparable to the 6H-SiC and 3C-SiC crystal structures. The energy band gap of a sample grown at 160 MHz with growth temperature of 200 °C was 3.19 eV which is approximately the energy band gap of 4H-SiC (3.20 eV). In conclusion, this enhancement method in growing SiC QDs can be applied in future study in terms of its material properties and also its application in nanodevice technology.