PREPARATION OF PHOTOLUMINESCENT NANOSIZED Si BY PULSED LASER ABLATION

利用不同的技术制备了多种具有纳米级晶体包裹体的硅基薄膜，用于可见光发射。脉冲激光烧蚀是制备高质量钙钛矿氧化物薄膜的研究热点。该制备技术有一个非常独特的特点，即沉积的颗粒大小分布广泛，从单原子或双原子到微米大小的巨大簇状物，即所谓的液滴。本研究采用脉冲激光烧蚀法在氧化硅基体中制备含硅晶夹杂物的非均匀氧化膜。采用脉冲激光烧蚀法，利用波长为193 nm的ArF准分子激光器和硅靶，在氧气和氦气混合气体中制备了室温下熔融石英衬底上的氧化硅薄膜。为了沉积薄膜，激光束被聚焦到一个小区域，得到3.5 J/cm^2。沉积后用0.5 J/cm^2的ArF激光照射增强光致发光。进行了光致发光、x射线衍射和拉曼散射测量。采用氩离子激光激发，在室温下进行了光致发光测量。通过脉冲激光烧蚀得到的As沉积膜是透明的硅氧化物，包括尺寸达数十nm的硅晶体，这些纳米以上的大晶体不可能是光致发光中心。事实上，沉积膜表现出非常弱的光致发光。然而，经过1000次激光照射后，光致发光强度急剧提高了两个数量级。光致发光光谱以波长550nm为中心。这种显著的增强可归因于纳米硅晶体的形成或缺陷密度的降低。

A variety of silicon-based films with nanosized crystallite inclusions have been prepared for visible photoemission using various techniques. Pulsed laser ablation has been attracting much attention for preparation of high-quality perovskite oxide films. The preparation technique has a quite unique feature that depositing particles have a broad distribution in size from mono- or diatomic species to huge clusters, so called droplets, with a micron size. In this study, for preparation of inhomogeneous oxide film with silicon crystallite inclusions in silicon oxide matrix, the pulsed laser ablation was employed.Silicon oxide films were prepared on fused quartz substrates at room temperature by pulsed laser ablation using silicon target and an ArF excimer laser with wavelength of 193 nm in a mixture of oxygen and helium gases. For depositing films the laser beam was focused into a small area resulting in 3.5 J/cm^2. After the deposition an ArF laser irradiation with 0.5 J/cm^2 was performed for enhancing photoluminescence. Photoluminescence, X-ray diffraction and Raman scattering measurements were performed. The photoluminescence measurement was carried out at room temperature using Ar- ion- laser excitation.As- deposited films obtained by pulsed laser ablation was found to be transparent silicon oxides including silicon crystallites with size as large as tens of nm. These large crystallites above nanosize were not expected to be photoluminescent centers. In fact, the as- deposited film shows a very weak photoluminescence. However, after the laser irradiation of 1000 shots the photoluminescence intensity was dramatically increased by two orders of magnitude. The photoluminscence spectrum was centered around 550 nm in wavelength. This dramatic enhancement can be attributed to a formation of nanosized silicon crystallites or a reduction of the defect density.