Structural optimization and quantum size effect of Si-nanocrystals in SiC interlayer fabricated with bio-template

Amorphous SiC/Si multilayers were fabricated using alternately magnetron sputtering of SiC and electron beam evaporation of Si targets. The as-deposited films were annealed at different temperatures from 800 till 1000 °C to form Si-nanocrystals (Si-NCs) and study the layered structural stability by different analytical techniques, including x-ray reflectivity (XRR), x-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), and surface morphology by atomic force microscopy (AFM). XRR demonstrated that SiC/Si multilayers annealed at temperatures up to 1000 °C retain their layered structure. XRD and TEM confirmed the formation of Si-NCs after annealing at ≥800 °C. The Si-NCs size estimated from the TEM images is ∼4 nm for the multilayered sample with alternating 2 nm SiC and 4 nm Si layers. SIMS revealed that SiC/Si multilayers annealed at 800 °C possess the best periodic structure possibly due to the lowest carbon interdiffusion as compared to the samples annealed at higher temperatures. AFM micrograph confirmed that SiC/Si multilayers annealed at 800 °C characterized by the lowest surface roughness having RMS value of 0.123 nm as compared to the samples annealed at 900 °C and 1000 °C having RMS values of 0.207 and 0.530 nm, respectively. Size-controlled 3D array of Si-NCs separated by SiC barriers was fabricated by neutral beam etching of annealed SiC/Si multilayers with different Si layers thickness from 2 to 6 nm using a bio-template consisting of ferritin molecules. The size-dependent band gap energy of Si-NCs was estimated by optical spectroscopy to vary from 1.61 till 1.92 eV owing to the quantum confinement effect as the Si-NCs size decreases, which is appropriate for application in Si-based tandem solar cells.