【作者】 刘彩霞；

【导师】 甄聪棉；

【作者基本信息】 河北师范大学 ， 凝聚态物理， 2008， 硕士

【摘要】 自1990年Canham发现多孔硅(PS)室温下发射可见光的现象,人们对多孔硅引起足够重视。多孔硅具有独特的物理微结构和显著的量子限制效应,以及与现有Si工艺兼容。多孔硅光致发光的发现意味着全硅基光电集成的可能,具有极其重要工业应用潜力。目前,人们对多孔硅的形成机理、发光现象以及在技术上应用的可能性做了很多有意义的工作。经过阳极氧化处理后得到的多孔硅能发射较强的近红外、可见和近紫外光,而人们最关注的仍然是多孔硅在整个可见光波段的发光。我们实验中采用直流电化学腐蚀的方法在不同腐蚀条件下制备了多孔硅样品,研究了其结构和可见光波段的发光特性。利用荧光分光光度计测试了样品的光致发光(PL)特性。用扫描电子显微镜(SEM)和原子力显微镜(AFM)研究了多孔硅的表面形貌。利用傅立叶变换红外光谱(FTIR)测试了PS内部的化学成键情况。在其它腐蚀条件不变的情况下,改变腐蚀电流密度。SEM观察到,电流密度较小时,腐蚀初期形成的凹坑数较少,相邻孔之间的孔壁较厚,即硅线较粗。随着氧化电流密度增加,相邻孔之间的孔壁变薄,硅晶粒线度变小。AFM图观察到在多孔硅的表面存在明显的类似“小山状”的硅柱,顶部较尖。随着腐蚀电流的增加,孔洞分布密度变稠,这表明更多的Si被腐蚀掉。PL谱测试表明,在可见光波段,我们的样品存在3个发光峰,即360 nm,380 nm和470 nm。380 nm的发光来自于PS的表面态中空穴电子复合。360 nm处的发光被认为与PS表面氧化而形成的SiO2有关。470 nm处的发光与阳极腐蚀脱落碳与Si反应形成的SiC有关。电流密度的改变并没有引起380 nm处峰位的蓝移或者红移。FTIR谱测试存在3个明显的吸收峰位,它们分别位于610 cm?1、734 cm?1和1110 cm-1。610 cm?1的吸收峰来自于多孔硅中的Si–Si伸缩振动峰,734 cm?1的红外吸收峰归因于Si–C的振动(Si1?xCx,x<0.5),1110 cm-1的吸收峰由于多孔硅表面氧化形成的SiO2中的Si-O-Si反对称伸展振动模式。腐蚀电流密度过大,腐蚀液会对Si表面形成一种抛光作用,在我们的实验中得到的最佳腐蚀电流密度为50 mA/cm2。当腐蚀液的浓度和腐蚀电流密度不变,改变腐蚀时间。从AFM形貌图可以看出,多孔硅的孔隙率增加,从而造成表面态的增加,380 nm处的紫峰峰强度随腐蚀时间的延长明显增强。继续增大腐蚀时间,多孔硅表面出现抛光现象。从我们的实验得出,当腐蚀电流为50 mA/cm2时,最佳的腐蚀时间是30 min。在一定的条件下腐蚀得到PS,随着放置时间的增加,表面的氧化硅层增厚,表面氧化的PS结构日趋稳定,缺陷密度相对降低,使得与缺陷有关的辐射复合减少。在相同的电流密度和阳极氧化时间的条件下,改变电解液浓度。PL谱测试表明:腐蚀液的浓度越大,对硅表面有更强的腐蚀作用,形成的表面态就更多。同时碳从电极上脱落的速度随腐蚀液浓度的增大而加快,形成了更多Si-C。更多还原

【Abstract】 Investigations on porous silicon (PS) with strong room-temperature visible emission by Canham have stimulated much effort to explore its emission properties. PS film because of its unique microstructure, significant quantum effect, and the compatible process with Si IC industry has a great potential in a variety of optoelectronic device applications. Recently, much meaningful work has been done on the formation mechanism, the luminescence phenomena of PS, and its possible applications. Porous silicon films were fabricated by direct current (DC) electrochemical method under different conditions in this work. The microstructure and photoluminescence properties of PS in visible waveband were studied.Fluorescence spectrometer and scanning electron microscope (SEM) were employed to characterize the photoluminescence and surface morphology of samples. Fourier transform infrared spectroscopy (FTIR) was used to characterize its chemical information.Keeping other experiment conditions unchanged, we only change the current density. SEM images show that when we applied small current, the number of the hole formed on the Si is little. The wall between the holes is relatively thick. That is to say, Si line is wide. As the current density increased, the wall between holes becomes thin and Si line is slim.“Hill-like”silicon mounds on the surface of PS were observed by AFM. As the current density increased, the silicon mounds became dense. This indicates that more silicon was etched. PL measurements show that there are three emissions located at 360 nm,380 nm and 470 nm, respectively, in our sample. The peak at 380 nm comes from the combination of the holes and electrons in the surface states of PS. The peak at 360 nm is thought to be related with SiO2 from the surface oxidation of PS. The signal at 470 nm is caused by the Si-C bond formed by the reaction between C breaking off from anode and Si. The change of current doesn’t cause the position shift of 380 nm peak. There exist three significant absorption peaks in FTIR. They are located at 610 cm?1, 734 cm?1 and 1110 cm-1 respectively. The peak at 610 cm?1 is due to the stretching vibration of Si-Si bond. 734 cm?1 absorption is attributed to the vibration of Si-C (Si1?xCx,x<0.5). 1110 cm-1 is caused by the antisymmetric stretching vibration of Si-O-Si in SiO2 formed by the surface oxidation of PS. We also note that if the current is too large, the solution will polish the surface of PS. In our experiment, the optimal current density is 50 mA/cm2. Keeping the solution concentration and current density constant, only etching time was changed. AFM observation shows the increase of the porosity of PS with the time increased, which caused the surface states increase. The intensity of 380 nm peak increased significantly with the increase in etching time. Increasing the current further, the surface of PS was polished. When the etching time is 30 min, we can obtain the most intense emission.PS was placed in the atmosphere. As the aging time increase, the oxidation layer becomes thick. The microstructure of PS coated with an oxidation layer becomes stable. The defect density decreased. The combination related with the defects becomes small.Only the solution concentration is changed, while other experiment conditions unchanged. PL measurements indicate that the larger the solution concentration is, the more obvious etching effect shows. The rich surface states bring more intense emission. At the same time, there will be more and more C deciduous from anode, forming more Si-C.更多还原