Many strategies have been developed to improve silicon's and germanium's light emission efficiency

such as band gap engineering and quantum confinement in low-dimensional structures.Porous silicon

silicon nanocrystals and germanium nanocrystals in the SiO

2

layer are being investigated actively as some means of improving the light-emission properties of silicon and germanium.Many physical mechanisms have been proposed to explain the photoluminescence(PL)in low-dimensional nanostructures.In this paper

some kinds of low-dimensional nanostructures were formed by etching with laser irradiation on Si

1-x

Ge

x

sample.Dot structure and line structure was formed

respectively

on the SiGe film after anodizing and irradiating for 5 min and 10 min;after 15 min

nano-strap pieces structure was formed when the SiGe layer was dug up.Due to the impaction of ion and the irradiation of laser

after etching with laser irradiation for 30 min

the Si

1-x

Ge

x

layer was almost peeled

then porous structure was formed on the substrate.After anodizing and irradiation

the porous structure samples were oxided by annealing treatment in the furnace at 800℃ for different time.We studied the evolution of photoluminescence with annealing time.It was found that the PL peak at 724 nm increases obviously on the porous structure where the Si nanocrystals/SiO

2

Ge nanocrystals/GeO

2

system exists before annealing treatment.After annealing for 20 min

the PL intensity reduces obviously.However

the PL intensity incresases again after annealing for 30 min

and that PL emission shows blue-shift obviously to 683 nm.When annealing time was longer than 90 min

the PL spectra vanishes.The change of PL emission of SiGe sample cannot be explained by quantum confinement(QC)or quantum confinement-luminescence center(QCLC)model.According to the QC and QCLC model

a new model of quantum confinement-the trap states of the interface between some oxides of silicon and nanocrystal was proposed for interpreting the change of PL emission in Si

1-x

Ge

x

alloys.Through this model

we hope to solve the problem of "critical size" in QC and QCLC models.In this model

the photoexcitation occurs in Si nanoclusters and Ge nanoclusters embedded in the oxide layer

where the band gap opens by quantum confinement.The enhancing photoemission occurs in the interface states of the Si oxide adjacent to the nanocrystals only when the level of the excitation states opened by QC is higher than that of the interface states

so that the interface states can trap the electrons photoexcited.It is clear that after deeper oxidation on SiGe

the level of the excitation states opened is lower than that of the interface states due to higher level of oxide states where the PL band is weaker.The wavelength of intensive PL peaks is also determined by the level position of the trap states in the crystal-oxide interface due to oxidation conditions in laser irradiation and annealing.We think that the energy state distribution is various in different crystals and different oxide interface states which play an important role for explaining the change of frequency and intensity of PL.