镶嵌在氢化氮化硅中纳米非晶硅粒子光吸收的模拟

采用量子限制效应模型对镶嵌有纳米非晶硅粒子的氢化氮化硅薄膜的光吸收进行了理论模拟,探讨了由吸收谱分析给出该结构薄膜光学参数的方法,并通过对不同氮含量样品的讨论给出了量子限制效应和纳米硅粒子表面的结构无序对薄膜光吸收特性的影响规律。分析结果表明,随氮含量的增加,薄膜有效光学带隙增大,该结果与薄膜中纳米硅粒子平均尺寸的减小引起的量子限制效应的增强相关,而小粒度纳米硅粒子比例增加所引入的较高微观结构无序度和较多缺陷将会导致薄膜低能吸收区吸收系数增加。

Simulation of Optical Absorption Spectra of Amorphous Silicon Nanoparticles Embedded in Hydrogenated Silicon Nitride

Optical absorption analysis is one of the most important technologies for understanding the microstructure of thin films and their band gap properties.For silicon nanostructures,the traditional Tauc method that succeeded in amorphous material is not applicable since the optical absorption of silicon nanostructures would be affected not only by the quantum confinement effect of nanoparticals in the films but also by their concomitant microstructural disorder.In this paper,an optical absorption model for the silicon nitride thin films embedded with amorphous silicon nanoparticles(a-Si NPs/SiNx) is proposed based on quantum confinement effect assuming that a-Si NPs acts a system of three-dimensional confinement quantum dots with a size distribution and the silicon nitride matrix provide a potential barrier.The optical absorption of the films is mainly determined by optical excitation in the system of a-Si NPs.Through simulating the optical absorption spectra of the a-Si NPs/SiNx thin films with above model,we have obtained the size distribution of a-Si NPs and the mean optical gap of the thin films.The effect of surface structural disorder of the a-Si NPs on the optical absorption of the films is also discussed based on the Infrared optical absorption analysis.A good agreement between the simulated optical absorptions and the experiment results has been obtained in high energy region.Whereas,the deviation of simulated optical absorptions from experiment results in low energy region shows an increased trend.The results show that the quantum confinement effect of a-Si NPs determines the optical absorption of the thin films in high-energy region and the increase of the optical gap is correlated to the decrease of the mean size of the nanoparticles with increasing nitrogen contents.The optical absorption in the low-energy region is mainly generated from the optical excitation in the sub-band states that related to structural disorder and their enhancement in intensity with increasing nitrogen contents can be accounted by the increase of the portion of small a-Si NPs in the films.