【作者】 马阳进；

【导师】 沈文忠；

【作者基本信息】 上海交通大学 ， 凝聚态物理， 2012， 硕士

【摘要】 随着半导体电子器件集成程度逼近量子隧穿的尺寸极限,维持摩尔定律已面临严重挑战。硅基光子学器件由于其更快速,更稳定,更低能耗等优点而得到了广泛的关注。由于体硅材料本身间接带隙的限制,如何设计硅或与硅基集成的其他材料的微纳结构,甚至直接利用硅材料的非线性光学性质进行应用是研究的主要关注点。本论文主要集中在: (1).用开孔Z扫描(OA Z-scan)方法探测了氢化纳米硅(nc-Si:H)薄膜的非线性吸收(nonlinear absorption, NLA)性质; (2).研究了nc-Si:H薄膜微米尺度飞秒激光晶化效应及其引起的新型光学吸收机制;(3)通过实验和理论计算研究了硅基上生长的氧化锌(Zinc Oxide, ZnO)微米塔中回音廊效应(whispering gallery mode, WGM)和准回音廊效应(quasi-WGM)引起的固定模式的光发射。nc-Si:H的硅纳米晶(Si-nc)镶嵌于无序的氢化非晶硅网络中(a-Si:H)。由于可用化学气象沉积(plasma-enhanced chemical vapor deposition, PECVD)的方法生长,nc-Si:H可以被集成到多数的硅基光电子器件中。以前对nc-Si:H的研究多侧重于线性光学和电学性能,本论文对nc-Si:H的非线性光学性质进行了详细研究。我们观察到,如果飞秒激光入射光子能量略低于能带时,nc-Si:H会呈现出从饱和吸收(saturable absorption, SA)到反饱和吸收(reverse saturable absorption, RSA)的转变。我们认为这种NLA的机制与nc-Si:H的带尾态密切相关。这种SA到RSA转变非常灵敏并且具有很强的可调控性,可通过调节入射光波长,光强与nc-Si:H的能带来实现,将有希望用于高灵敏的非线性光学器件中。同时在Z-scan实验过程中,我们发现当入射激光光强超过一定阈值时,样品将会发生突变,但突变点具有非常好的RSA信号,且此信号与入射光的波长和光强都无关。我们在极小入射光强下测得了非常强的Z-Scan RSA信号。我们提出了微米尺度的激光晶化模型,并依此建立了空间非均匀线性吸收(linear absorption, LA)理论来成功解释了观察的实验现象。据我们目前所知,这是一种全新的解释Z-scan结果的理论。此模型已被显微拉曼面扫描(micro-Raman mapping)实验进一步地证实。此项工作的实验与理论部分都将对设计新型的弱光非线性光学器件有所裨益。最后,本文还研究了用化学气相沉积(chemical vapor deposition, CVD)方法在硅基上生长的ZnO微米塔的激光模式。在355nm纳秒激光激发下,我们在ZnO微米塔阵列的光致发光(photoluminescence, PL)谱中观察到了两个固定模式的发射。通过全反射理论计算,我们认为光应该出射于微米塔中部平台,两个模式分别为WGM的横磁波TM8和quasi-WGM的横磁波QTM8模式。阴极发光(Cathodoluminescence, CL)实验很好地证实了理论计算。我们正在建立模型用FDTD法进行进一步的仿真模拟。以上研究得到了科技部重大研究计划课题(2010CB933702)和国家自然科学基金重点项目(10734020)和(11074169)的资助。特此感谢!更多还原

【Abstract】 Maintaining the development of Moore’s Law has been a great challenge since the integration scale of electronic devices is approaching its limit of quantum tunneling. Silicon based photonic devices has been widely attracted attention because of the merits faster operation speed, more stable properties, lower energy consumption. However, bulk silicon is limited in photonic application because of the indirect band gap. How to design micro- and nanostructures of silicon or other materials that can be integrated in with silicon, or to utilize the nonlinear optical properties of silicon for application is the main focus in research.This thesis is focused on three main topics: (1). studied the nonlinear absorption (NLA) properties of hydrogenated nanocrystalline silicon (nc-SI:H) with open aperture (OA) Z-Scan technique; (2). investigated the micrometer-scale femtoscond laser crystallization of nc-Si:H and the new absorption mechanism induced by the crystallization; (3). experimentally and theoretically studied fixed mode light emission in ZnO microtower from whispering gallery mode (WGM) and quasi-WGM enhancement.The silicon nanocrystals (Si-ncs) of nc-SI:H is embedded a disordered amorphous Si:H matrix. Since it can be grown by plasma-enhanced chemical vapor deposition (PECVD), nc-Si:H is readily able to be integrated with most Si-based devices. Previous research on nc-Si:H laid emphasis on its linear optical and electronic properties, in this thesis, the main focus is to study the nonlinear optical properties. It is observed that, III if the photon energy of the femtosecond laser lies slightly below the band gap, nc-Si:H will show a switch from saturable absorption (SA) to reverse saturable absorption (RSA). The mechanism of this NLA behavior is tightly related to the band tail states of nc-Si:H. And the switch from SA to RSA is high sensitive and tunable. It can be easily tuned by incident wavelength, intensity and the band gap of nc-Si:H. Judging from this excellent property, nc-Si:H is a potential material for high sensitive nonlinear photonic devices.During the Z-scan experiment, it is also observed that once the power of the incident laser exceeds a threshold, the samples will suffer an mutation. However, mutated spot owns excellent RSA property, and the RSA signal from Z-scan is independent of both optical power and wavelength of the incident light. We gained extremely strong RSA Z-scan signal in a really small power. We proposed a micrometer-scale laser crystallization model and, based on this model, we successfully explained the experimental phenomenon by a linear absorption (LA) theory—spatially non-uniform LA theory. To the best of our knowledge, this is a totally new theory to explain Z-scan results. The model is further confirmed by micro-Raman mapping experiment. Both the experimental and theoretical part of this work will be instrumental in designing new type low-intensity nonlinear optical devices.At last, in this thesis, we studied the light emission properties of ZnO microtower that were prepared by chemical vapor deposition (CVD) in a silicon substrate. Pumped by a 355nm nanosecond laser, we observed two fixed modes in the photoluminescence (PL) spectrum of ZnO microtowe array. Calculation results of total internal reflection showed that the observed two modes came from the contribution of whispering gallery mode (WGM) and quasi-WGM resonance in the middle flat part of the microtower. One of them is TM8 mode and the other QTM8. Calthodoluminescence (CL) experiment further verified our theoretical calculation. We will set up a model to further simulate the optical properties of a single microtower by finite-difference time-domain (FDTD) method.This work is supported by the National Major Basic Research Project of 2010CB933702, and Natural Science Foundation of China under contracts 10734020 and 11074169.更多还原