Microstructure and optical absorption properties of Si nanocrystals fabricated with low-pressure chemical-vapor deposition

We report a simple technique fur fabricating a layer of isolated Si quantum dots on SiO2 glass substrates. This technique uses conventional low-pressure chemical-vapor deposition for an extremely short deposition lime in the early stage of poly-Si film growth, The layer after a deposition time of 60 s has isolated Si nanocrystals 5-20 nm in diameter and 2-10 nm in height. The measurements of optical absorption coefficient a show that the absorption edge for Si nanocrystals shifts io higher energies compared Id that of bulk Si, indicating a widening of the energy gap caused by quantum size effects. The linear relationship (alpha hz) (1/2) against hv suggests that the Si nanocrystal, whose diameter is as small as 10 nm, basically maintains the properties of an indirect band-gap semiconductor. Special attention must be paid to the Brownian migration of Si nanocrystals Tor fabricating Si quantum dots. (C) 1996 American Institute of Physics.