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

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Abstract
We report a simple technique for 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 time 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 α show that the absorption edge for Si nanocrystals shifts to higher energies compared to that of bulk Si, indicating a widening of the energy gap caused by quantum size effects. The linear relationship (αhν)1/2 against hν 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 for fabricating Si quantum dots.