To research the photoluminescence mechanism of nanocrystalline silicon (Si) and to give some experimental backing for the fabrication of Si light emitting devices

we tried to make Porous Anodic Alumina Template (PAA) by using a two-step anodization technique. The pulsed laser deposition (PLD) was used to deposit a layer of Si on the PAA substrate through a two-step deposition procedure in vacuum.After that

we got a combined film of Si and PAA. Next

put the combined film into acid solution to get rid of the PAAsubstrate. Then we got the Si film with Si nanowires scattered on it. Scanning electronic microscopy (SEM)and X-ray diffraction (XRD) were used to study the structure

morphology

crystalline phase and the composition of the film. The result showed that this Si structure is amorphous phase. The diameter of the nanowires is about 67.5 nm

the length is about 100 nm

the number density is about 10

11

/cm

2

. This Si film possess of very large surface

so surface state and the substances it adsorbed played an important role in photoluminescence.The photoluminescence spectrum could be decomposed into two parts. One is a broad emission band whose peak wavelength was about 610 nm with a full width of half maximum (FWHM) is about 150 nm. The other included 17 sharp peaks

each of them has fine structure. The wavelength intervals between the sharp peaks are different

but the energy intervals are equal.We analyzed the structure characteristics of the sample and used the Quantum Confinement Effect model and the Surface Photoluminescent Center model to explain the photoluminescence spectrum. Accordingly

there are two luminescence processes: 1. Electron-hole pairs recombined in the Si nanocrystallines and the photons pass through the surface to come out. When the samples were excited by laser (488 nm)

it produced a great deal of electrons and holes. After some relaxation process

quite a few electrons and holes recombined in the Si nanocrystallines and give off light which forms the broad peak of the spectrum whose peak wavelength was about 610 nm and the FWHMwas about 150 nm. 2.An electron (or a hole) relaxed to the surface luminescence center and recombined with a hole (or an electron) and gave off light. In this way

the photons came out from the surface luminescence center directly. When the sample was excited by laser (488 nm)

it produced a great deal of photon generated carriers. Because of the quantum confinement effect

the band-gap energy of Si nanocrystallines was increased to the visible light range. The energy of the photon generated carriers is also in the visible light range. Some of the photon generated carriers wouldn't stay inside; they came to the surface by diffusion. During the diffusion process

they would come into collision with atoms and electrons

so they would lose energy gradually.This is a relaxation process in fact. They would be captured by the surface luminescence center in the end. As the surface luminescence center was vibrating

so the intervals between excited energy levels were equal.We also proposed a new energy band model and even calculated the quantum numbers of the excitation bands which correspond to the small sharp peaks.