Fabrication and characterization of Si1-xGex nanocrystals in as-grown and annealed structures: A comparative study

Multilayer structure comprising of SiO2/SiGe/SiO2 were obtained by depositing SiO2 layers using reactive direct current magnetron sputtering (dcMS), whereas, Si and Ge were co-sputtered using dcMS and high impulse power magnetron sputtering (HiPIMS), respectively. The as-grown structures subsequently underwent rapid thermal annealing (550 – 900 °C for 1 min) in N2 ambient atmosphere. The structures were investigated using X-ray diffraction, high-resolution transmission electron microscopy along with photoconductive analysis, to explore structural changes and constituent properties. It is observed that the employment of HiPIMS facilitates the formation of SiGe nano-particles (~ 2.1 ± 0.8 nm) in the as-grown structure, and that presence of such nano-particles acts as a seed for heterogeneous nucleation, which upon annealing results in formation of periodically arranged columnar self-assembly of core-shell SiGe nanocrystals. Consequently an increase in photocurrent intensity by more than an order of magnitude was achieved by the annealing. Furthermore, a detailed discussion is provided on strain development within the structures, the consequent interface characteristics and its effect on the photocurrent spectra.