Some kinds of low-dimensional nanostructures can be formed by irradiation of laser on the SiGe alloy sample.Dots structure and lines structure on the Si

1-x

Ge

x

film were formed under a weaker irradiation of laser.Nano-strap pieces structure after digging up the Si

1-x

Ge

x

layer with a stronger laser.Porous structure on the substrate under anodizing and irradiating for 30 min

when the Si

1-x

Ge

x

layer is almost dug out;oxygen distribution on the porous structure is measured.We have studied the photoluminescence(PL) of the porous structure of SiGe where the PL intensity at 725 nm wavelength increases obviously.The effect of intensity-enhancing in the PL peaks cannot be explained within the quantum confinement alone.A new model of three-level system associated with the crystal-oxide interface state has been proposed for interpreting the PL peak at 725 nm wavelength:An injection photon excites an electron in the top of valence band to jump up into the bottom of the conduction band which is called to an absorption jumping process whose gap width increases because of the quantum confinement effect.It is a fast process for electron to jump from the valence band to the conduction band.Then the electrons are very rapidly caught into the interface state distributing in the region below the conduction band.These trap states have a certain distribution round the center state of 1.7 eV energy level.We think that the states distribution is probably related to the frequency distribution of the PL emission.Electrons in the interface state have long lifetimes

and population inversion between the top of the valence band and the interface state is thus possible from which we can explain the enhancing effect of the PL peak at 725 nm wavelength.