Development of nc-Si/a-SiN_x:H Thin Films for Photovoltaic and Light-Emitting Applications

摘要

Silicon nanocrystals embedded in amorphous silicon-nitride matrix (nc-Si/a-SiN_x:H) were prepared using RF-ICPCVD at 13.56 MHz, by changing the flow ratio R = NH_3/SiH_4 in the H_2-diluted plasma at 300 ℃. Nitrogen incorporation in silicon network controls the nature of nanocrystallinity in various ways: by reducing overall crystallinity, however, enhancing the ultra-nanocrystalline component, efficiently reducing the average grain size from 14 to 2.2 nm, thereby increasing the optical band gap, and simultaneously increasing the amount of thermodynamically preferred crystalline grains exhibited by the relative dominance of (220) crystallographic orientation. The nc-Si/a-SiN_x:H films exhibit strong blue light emission that consists of two peaks at 413 and 438 nm and two shoulders around 467 and 498 nm, the relative changes of which are associated, respectively, to the rising concentration of Si ultra-nanocrystals and enhanced radiative Si dangling bonds at growing nitrogenation of the network along with subsequent weakening of the effect of oxygen contaminant at relatively amorphous structure. Size reduction of silicon nanocrystals with simultaneous control of its growth at thermodynamically preferred (220) crystallographic orientation within wide band gap nc-Si/a-SiN_x:H that exhibit strong blue light emission, deserves enormous promise towards efficient utilization in the fabrication of third-generation all-silicon tandem structure solar cells and light emitting devices.