脉冲激光沉积法制备的纳米硅薄膜的结构与光学性质

采用二次阳极氧化法,制备了多孔氧化铝模板。在真空背景下,用脉冲激光沉积法,在多孔氧化铝模板上沉积一层硅,制成了硅与多孔氧化铝的复合膜,然后用盐酸将多孔氧化铝模板完全腐蚀掉,制备均匀分布着硅纳米线的硅膜。用扫描电子显微镜、X射线衍射、光致发光对纳米硅的结构和光学性质进行了测试分析。结果表明:硅纳米线的直径约为67.5nm,长度约为100nm,数密度约10¹¹/cm²。光致发光谱是可见光范围内的一个宽发射峰,上面叠加了许多具有精细结构的尖峰,尖峰之间的波长间隔不相等,但能量间隔相等。分析了样品的结构特点,利用量子限制模型和表面发光中心模型对光谱进行了解释,提出了一个新的能级模型,求出了各个尖峰对应激发态能级的量子数。为探讨纳米硅的发光机制和实现硅发光器件的制备提供了实验依据。

Structural and Optical Characteristics of Nano-crystalline Silicon Films Fabricated by Pulsed Laser Deposition

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 PAA substrate. 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 FWHM was 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.