含氧硅基材料的荧光特性研究

The photoluminecence properties of oxygen doped Si-based material

分别采用等离子体增强化学气相沉积(PECVD)技术和金属辅助化学蚀刻的方法制备了纳米硅/二氧化硅(nc-Si/SiO_2)多层膜和多孔硅纳米线(Si NW)两种含氧的硅基材料.借助透射电子显微镜和扫描电子显微镜对样品的微结构进行表征,在此基础上,利用稳态和时间分辨荧光光谱仪对两种材料的荧光特性进行测量.实验结果表明nc-Si的尺寸越小,多孔Si NW内的孔洞越多,样品的发光越强,但是发光峰不发生移动.在波长为355nm,脉宽为6ns的激光激发下,两种材料都具有微秒(μs)的荧光寿命,对应于载流子从与氧相关的局域态发生辐射复合的过程.将光致发光(PL)强度的增强以及荧光寿命的增大归因于样品内辐射复合中心的增多.同时,在波长为375nm,脉宽为75ps的激光激发下,两种样品在纳秒(ns)范围内均没有检测到荧光衰减信号.

The nanocrystalline Si（nc-Si）/SiO2 multilayers were deposited in a traditional plasma enhanced chemical vapor deposition（PECVD）system,and a two-step metal-assisted chemical etching method was employed to prepare porous Silicon nanowire arrays（Si NW）. The size of nc-Si could be controIled by adjusting the deposition condition, while the porosity density of the Si NW could be tuned through controlling stoichiometric proportions and etching time. The microstructure of two samples was characterized through transmission electron microscopy and scanning electron microscopy, then their fluorescence properties were measured by using the steady and time-resolved fluorescence spectrometer. The steady photoluminescence（PL）was measured under 325 nm He-Cd continues laser excitation,the PL centered at 900 nm for nc-Si/SiO2 multilayers was observed. Meanwhile, for the Silicon nanowire arrays,the PL peak was 720 nm. With decreasing the average size of nc-Si or increasing the porosity density of Silicon nanowire arrays, the PL intensity gradually enhances, while the PL peak remains unchanged. The time- resolved photoluminescenee decay spectra were measured by utilizing an Edinburgh instruments （FLS980） fluorescence spectrophotometer. Two excitation sources were equipped, one was a EPL-375 picosecond （ps）pulse diode laser（λ= 375 nm, pulse duration 75 ps and repetition frequency 5 MHz） ,the other one was a frequency-tripled Nd：YAG nanosecond（ns）laser（λ= 355 nm, pulse duration 6 ns and repetition frequency 10 Hz）. It is shown that the two kinds of material both exhibit microsecond（μs） fluorescence lifetime under nanosecond（ns）laser excitation,the microsecond（gs） PL decay could be attributed to the radiative recombination of photo-generated carriers via the oxygen-related localized states at the interfacial region. The enhanced PL and longer fluorescent lifetime could be ascribed to the increase of radiative recombination center. Meanwhile, all samples don＇t have the nanosecond PL decay component when exited by picosecond（ps）laser.