Nonlinear And Micro- And Nano-Hotonic Properties Of Silicon Based Materials

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.