氧化硅层厚度对Si/SiO2界面电子态结构与光学性质的影响

在氧化硅上生长纳米硅晶,保持氧化硅的直接带隙结构,降低其能带带隙,以用于发光和光伏。采用基于密度泛函理论的第一性原理研究了块体α-方石英、薄膜α-方石英、Si/SiO₂界面的电子态结构和Si/SiO₂界面的光学性质。结果显示,其均为直接带隙半导体,当薄膜α-方石英厚度和Si/SiO₂界面氧化硅层厚度逐渐减小时,能带带隙均逐渐变大,表现出明显的量子限制效应。光学性质计算结果表明：Si/SiO₂界面虚部介电峰和吸收峰的峰值随氧化硅层厚度降低而显著升高,且峰位向高能量方向蓝移。使用脉冲激光沉积制备了氧化硅上硅晶薄膜,测量了Si/SiO₂界面样品的PL光谱,在670 nm处存在一个强的发光峰,在波长超过830 nm后,Si/SiO₂界面样品的发光强度不断升高。因此,可以通过控制Si/SiO₂界面氧化硅层厚度有效地调控Si/SiO₂界面的电子态结构和光学性质,引进边缘电子态,调控其带隙进入1～2 eV区间,获取硅基发光材料...     

量子受限效应和对称性效应对硅光子晶体禁带的影响

光子晶体不仅可以用来调控自发辐射, 还可以用来控制光的传输和局域. 采用平面波展开法进行模拟计算, 分析硅背景下的二维正方、三角晶格光子晶体散射基元的形状和空间取向对光子禁带的影响. 计算结果表明: 对称性和量子受限效应之间的竞争是导致光子晶体禁带宽度发生变化的原因.     

Band structure of silicon and germanium thin films based on first principles

In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties, in which directional optical properties can be exploited to enhance the performance of optoelectronic devices. First principles calculation based on density functional theory(DFT) with the generalized gradient approximation(GGA) are carried out to investigate the energy band gap structure on silicon(Si) and germanium(Ge) nanofilms. Simulation results show that the band gaps in Si(100) and Ge(111) nanofilms become the direct-gap structure in the thickness range less than 7.64 nm and7.25 nm respectively, but the band gaps of Si(111) and Ge(110) nanofilms still keep in an indirect-gap structure and are independent on film thickness, and the band gaps of Si(110) and Ge(100) nanofilms could be transferred into the direct-gap structure in nanofilms with smaller thickness. It is amazing that the band gaps of Si~((1-x)/2)Ge~xSi~((1-x)/2)sandwich structure become the direct-gap structure in a certain area whether(111) or(100) surface. The band structure change of Si and Ge thin films in three orientations is not the same and the physical mechanism is very interesting, where the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects.     

通信波段硅基气孔光子晶体的带隙特性及其物理模型研究

用平面波展开法对硅背景下的通信波段不同晶格类型和气孔形状光子晶体的能带结构进行数值计算与分析,提出了相应的物理模型.结果表明:利用光子受限效应和晶格对称性效应可以有效地调控光子带隙.随光子晶体填充率的增加,其约束光子的能力增强,光子带隙在一定范围内展宽且其中心频率蓝移;带隙随晶格对称性增加而变宽.对基元形状和旋转角度的研究发现,光子带隙随基元旋转角度变化具有周期性和对称性,表现出各向异性,由此优化出对应的不同晶格的最佳谐振腔型结构.     

硅量子点发光的激活及其物理模型研究

在真空或惰性气体中制备的硅量子点发光很弱,硅量子点表面被氢较好钝化后的发光也不强.硅量子点表面的硅氧键或硅氮键能破坏这种钝化并在带隙中形成局域电子态,在局域电子态对应的激活中心有很强的发光.可以用这种方式构建发光物质,控制硅量子点表面的键合可获得不同波长的发光.在硅量子点的发光激活处理过程中,退火是很重要的环节.对于硅量子点发光激活的机理,本文给出了相应的物理模型.实验证明,在600和700 nm波长附近观察到了激活硅量子点的受激发光,在1500 nm到1600 nm波长范围观察到了激活硅量子点的较强发光.     

Low-dimensional structures formed by irradiation of laser

Some kinds of low-dimensional nanostructures can be formed by irradiation of laser on the pure silicon sample and the SiGe alloy sample. This paper has studied the photoluminescence (PL) of the hole-net structure of silicon and the porous structure of SiGe where the PL intensity at 706nm and 725nm wavelength increases obviously. The effect of intensity-enhancing in the PL peaks cannot be explained within the quantum confinement alone. A mechanism for increasing PL emission in the above structures is proposed, in which the trap states of the interface between SiO₂ and nanocrystal play an important role.     

硅表面硅镱键合与量子级联结构的发光

用纳秒强激光脉冲制备了纳米硅和硅表面的硅镱键合结构,检测了纳米硅表面硅镱键合的发光特性,并对这种结构相应的光致发光(PL)和电致发光(EL)的动力学机理进行了研究。观察到纳米硅表面硅镱键合在700nm附近尖锐的强发光峰,结合第一性原理计算认为是硅镱键合在弯曲纳米硅表面的局域态发光;利用纳秒脉冲激光沉积技术(PLD)制备多晶硅薄膜,发现由硅镱界面的失配形成表面的突触,其上的硅镱键合产生带隙中的电子局域态,该局域态发光分布在1250~1650nm波长范围,有增强的EL发光;用PLD方法制备硅镱多层膜量子级联结构,测量到光通信窗口的多个发光峰,并观察到随膜层数增加且发光峰增多。     

多孔硅锗的制备及其近红外发光增强

用激光照射辅助电化学刻蚀硅锗合金样品能够形成多种低维纳米结构。在硅锗合金上形成的多孔状结构在波长为725 nm处有很强的光致发光(PL)峰,PL的增强效应不能单独用量子受限模型来解释。我们提出新的模型来解释这种低维纳米结构的PL增强效应。