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 qu antum dots on SiO2 glass substrates. This technique uses conventional low-pressure chemical-vapor deposition for an extremely short depositi on lime in the early stage of poly-Si film growth, The layer after a d eposition time of 60 s has isolated Si nanocrystals 5-20 nm in diamete r and 2-10 nm in height. The measurements of optical absorption coeffi cient a show that the absorption edge for Si nanocrystals shifts io hi gher energies compared Id that of bulk Si, indicating a widening of th e energy gap caused by quantum size effects. The linear relationship ( alpha hz) (1/2) against hv suggests that the Si nanocrystal, whose dia meter is as small as 10 nm, basically maintains the properties of an i ndirect 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.