Doping of nanocrystalline silicon with sulfur by gas-phase diffusion

Abstract

Sulfur-doped silicon nanoparticles were synthesized by annealing of nanosilicon powder in sulfur vapors at 500, 700 and 900 °C. The structures, chemical composition, optical and electrical properties of the samples were characterized using transmission electron microscopy, scanning electron microscopy, total x-ray fluorescence, x-ray diffraction, electron diffraction and absorption spectroscopy. The highest sulfur concentration was achieved at 700 °C with most of the dopant located on the surface, but it was evenly distributed inside the particles’ cores. Maximum level of doping equals to 0.5 % mol of sulfur, which is 4 orders of magnitude higher than the equilibrium solubility at 700 °C. Moreover, silicon microwires up to 300 μm long were discovered in samples synthesized at 900 °C. These samples also exhibits unusual properties, like direct band gap absorption and good conductivity even after being stored under air for a long time.