Hemispherical Si nanoquantum dots have been formed by self-assembled growth on SiO

2

/c-Si substrates using low-pressure chemical vapor deposition (LPCVD).The n-type Si(100) wafers were used as substrates in this study.After conventinal wet-chemical cleaning steps

2.3nm thick SiO

2

was grown on Si(100) at 1000℃ in 2% O

2

diluted with N

2

.Si nanocrystals were self assembled on the SiO

2

surface by LPCVD of SiH

4

in the temperature range of 560～590℃.The SiH

4

pressure was 0.27×10

2

Pa and the deposition time was 1min.We have experimentally studied the changes of PL efficiency and peak energy of Si nanodots with its heights h

c

.The results indicate that the PL efficiency remains unchanged when heights h e of Si dots are smaller than 5nm

while it dramatiaclly decreases as h

c

exceeds 5nm.The PL peak energy shifts from 1.28eV to 1.43eV when h

c

decreases from 5.5 to 0.8nm.We present a light emission mechanism

e.g.

quantum confinement effect interface light emission center radiative recombination model.The model indicates that the photoluminescence is not caused by the band to band transition

but caused by the recombination through radiative centers exsisting in the Si/SiO

2

interface region.Namely

the radiative centers might indirectly play a role for the photoluminescence.Since localized states exist in the Si/SiO

2

interface region

which originate in silicon oxygen clusters act as radiative recombination centers.When electron hole pairs are genarated by laser excitation

they are trapped by the radiative localized states through thermalization process.Since the carrier thermalization to the radiative recombination

the centers in the nanodots are considered to be very slow and less sensitive to the dot size

the radiative recombination rate of photo excited carriers is almost constant for h

c

<

5nm despite the enhancement of carrier transfer to the radiative recombination center by the quantum confinement effect.