【作者】 谢敏；

【导师】 杨德仁； 李东升； Lorenzo Pavesi；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2013， 博士

【摘要】 硅光子学是在硅上实现各种光学功能的技术,在生命科学、医学、信息、计算、传感、能源等领域有广泛的应用前景。其中最具吸引力的是：硅光子学可以最大程度地沿用现有的成熟的CMOS技术,在同一硅芯片上融合电子学和光子学,同时具有电子学的高计算容量和光子学的高通信带宽的优点,实现硅基单片集成。但是,其主要的限制因素是缺少硅基光源,即高效的发光二极管或硅激光器。考虑到体硅是间接禁带半导体的局限,研究者提出了很多策略来改善和实现硅基发光。在众多研究方案中,低维硅(纳米硅)由于量子限域效应和界面效应,成为非常有希望实现硅基发光的材料之一本论文系统研究了全硅基富硅氧化硅薄膜、掺硼富硅氧化硅薄膜的光电性能、物理机制和应用,致力于通过不同的方式得到高效的基于纳米硅的发光。取得主要创新结果如下：(1)利用等离子体增强化学气相沉积和后续高温热处理的方法,成功制备了高分布密度的硅(Si)纳米晶镶嵌于二氧化硅(Si02)基体的薄膜(富硅氧化硅薄膜)。通过氢钝化工艺,钝化了Si纳米晶/Si02界面非辐射态,提高了辐射效率。以优化的富硅氧化硅薄膜为有源层材料,结合微电子光刻工艺,成功制备了直径5-10μm的含Si纳米晶微盘谐振腔。当外在激光源的光注入使Si纳米晶自发辐射时,角对称微腔结构的全内反射效应使得宽的光滑的Si纳米晶发光带转化成在宽带上有一系列分立的尖锐的谐振峰的回音壁模式光谱。通过微区光致发光测试平台,获得了亚纳米线宽的回音壁模式谐振峰,在800nm处的品质因子高达3000,这在目前报导的Si纳米晶基微盘体系是最高值。我们指出,富硅氧化硅薄膜材料性能的优化(低损失,净材料增益),对品质因子的提高起关键作用。在Si纳米晶非均匀的宽增益谱范围,微盘谐振腔可能实现低阈值的激光行为。(2)首次通过连续波光谱,系统地研究了镶嵌在平面回音壁模式微谐振腔中的Si纳米晶的非线性动力学。观测到了特征线宽随激发功率增大而宽化的现象,指出这是由于激发载流子吸收损失引起的衰减。通过分析品质因子随激发功率的变化,得到了Si纳米晶的吸收横截面和激发载流子吸收相关损耗。观测到了模式峰位的非线性漂移,并对此建模得到了纳米晶材料的非线性折射率。理论结果还证实,观测到的谐振峰位的次线性蓝移和线性红移分别是由低泵浦功率下的激发载流子效应和高泵浦功率下的热光效应引起的。提取的Si纳米晶激发载流子折射率kEC=--1.07x10-23cm3和热光系数kT=1.46x10-4K-1,可以对光学有源微腔中的精细模式结构引入重要调制。(3)利用反应溅射结合共溅射和后续高温热处理的方法,制备了不同富硅量、不同掺硼量的掺硼富硅氧化硅薄膜。通过对化学成分、微结构的表征系统地研究了硼的掺杂对薄膜中镶嵌的Si纳米晶的影响。低富硅量(Si/O原子比～0.52)时,掺硼后的薄膜是亚纳米甚至原子尺度的Si聚集体；中等富硅量(Si/O原子比～0.67)时,掺硼后的薄膜是直径2-5nm的Si纳米晶镶嵌于SiO2基体中；高富硅量(Si/O原子比～1.1)时,掺硼后的薄膜是尺寸更大的Si纳米晶镶嵌于SiO2基体中,Si纳米晶的形状趋于椭圆,有重叠现象。通过X射线光电子谱Si2p和B1s心能级谱的研究,表明硼除了位于原子尺度/亚纳米尺度/纳米尺度Si中Si的替代位外,还存在于SiO2基体中或者Si聚集体与SiO2基体的界面处。(4)通过四探针电阻测试研究薄膜电学传导性能,观测到高富硅量薄膜掺硼后方块电阻率有4-5个数量级的下降。证实了硼原子对Si纳米晶实现了电学活性掺杂,从而显著提高了载流子浓度。中/低富硅量的掺硼富硅氧化硅薄膜经过高温热处理后,在室温下有强的白光光致发光,测得量子效率为几个百分点,这是Si基固态白光光源的一个重要探索成果。通过研究PL谱随富硅量、掺硼量、热处理温度的变化,揭示了发光中心位于纳米Si/亚纳米Si与基体的界面或基体中的原子尺度Si聚集体中,且发光中心是由硼促进形成的。硼含量相近时,中等富硅量的薄膜的发光强度高于低富硅量的薄膜,表明有进一步空间同时优化薄膜的电学和光学性能。综上,该体系有以下优点：由于制备的薄膜中所有元素都是“CMOS元素周期表”中的元素,与现有的微电子工艺兼容,制备成本低；通过调节富硅量、掺硼量和热处理温度,就能调节白光发光,工艺简单；硼的电学活性掺杂,可以改善薄膜的电学输运性能,更有利于实现硅基光电子集成。更多还原

【Abstract】 Silicon photonics is a technology to implement various optical functionalities in silicon. It has found a wide variety of applications, including life sciences, medicine, communication, computing, sensing, energy, and so on. The main interest is associated with the possibility to merge electronics and photonics in the same chip. This is very appealing since it allows exploitation of both the high computation capability of electronics and the high communication bandwidth of photonics. However, to achieve monolithically integrated silicon photonics, the main limitation is the lack of any practical Si-based light sources:either efficient light emitting diodes (LEDs) or Si lasers. Taking into account the main limitation that bulk Si is an indirect band-gap semiconductor, strategies have been proposed to improve the light emission and to realize Si-based light source. Among all the strategies, low-dimensional silicon (nano-Si) is quite promising due to quantum-confinement effect and interface effect.In this thesis, various approaches towards a Si-based light source based on nano-Si have been intensively investigated. The optoelectronic properties, the related physical mechanism and the applications of all-Si-based silicon-rich oxide (SRO) films and boron-doped silicon-rich oxide films have been systematically addressed. In the following, the primary achievements in this work are described.(1) High density of silicon nanocrystals (Si-NCs) embedded in silicon oxide film is achieved by plasma enhanced chemical vapor deposition (PECVD) technique and a successive high temperature annealing process. The passivation of nonradiative states and defects at the Si-SiO2interface is realized by performing H passivation of the Si-SiO2interface through standard forming gas annealing in order to increase the radiative yield without affecting the emission mechanism. Taken the optimized film as active layer combined with lithographic patterning and wet/dry etching processes, array of several thousands of5-10μm diameter microdisk resonators are formed. As Si-NCs posses a wide photoluminescence (PL) band in the visible and NIR region; when they are embedded in a dielectric microcavity, it is sufficient to observe whispering-gallery modes (WGMs) generated by optical injection via spontaneous emission of the Si-NCs. We report on subnanometer WGM resonances corresponding to quality factors (Q-factors) as high as3000around the wavelength of800nm, which to our knowledge are the highest among the previously reported values in Si-NC-based microdisk systems. We stress that the SRO material optimization (low-loss, positive material gain) should play a key role for further enhancement of the observed Q-factors of few thousands. Even with low while inhomogeneously broadened gain spectrum of Si-NC, microdisk resonators with similar Q-factors should be potential candidates to allow for a low-threshold laser action.(2) We report on a study of the recombination dynamics of Si-NCs embedded in a planar WGM resonator. Fundamental properties of exciton dynamics in Si-NCs, in particular their absorption cross-section and excited carrier-related losses, can be extracted from continuous-wave spectroscopy by analyzing the resonance linewidths at different excitation powers. Observation of nonlinear drifts of mode peak positions in the same experiment allows us to model the nonlinear refractive index of the nanocrystalline material. The theoretical results confirm that the observed sublinear blue and linear redshifts of resonance peak positions are induced by excited carrier effects and thermal heating at low and high pump powers, respectively. The extracted thermo-optic coefficient, kT=1.46×104K-1, and excited carrier refraction, kEC=-1.07×10-23cm3in Si-NCs, are of relevance since they may induce important modulation of the fine modal structure of an optically active cavity.(3) Boron-doped silicon-rich oxide films with a series value of Si excess and boron concentration are prepared by co-sputtering technique followed with the annealing treatment. The effect of boron-doping on the chemical composition and microstructure of Si-NCs embedded in silicon-oxide matrix are well studied. With low value of Si excess (Si/O atomic ratio～0.52), there are sub-nanometer scale Si or even atomic scale Si aggregates embedded in SiO2matrix. While for moderate value of Si excess (Si/O atomic ratio～0.67), there are Si-NCs with diameter of2-5nm embedded in SiO2matrix. And for high value of Si excess (Si/O atomic ratio～1.1), there are larger size Si-NCs embedded in SiO2matrix, which become elliptical-shaped and are overlapped. The investigation of X-ray photoelectron spectroscopy of Si2p and B1s core level spectra suggests that B atoms exist in Si substitutional sites of atomic scale or sub-nanometer scale or nanometer-scale Si as well as in silicon oxide matrix and/or in interface between matrix and Si aggregates.(4) For high values of Si excess, an almost4-5orders of magnitude decrease of the sheet resistance is achieved due to the significant increase of the carrier density by the electrically activated doping. For moderate and low values of Si excess, intense white photoluminescence from boron-doped silicon-rich oxide films is observed. The PL efficiency is of several percent, which is a promising result in Si-base solid state white light emitting. The influence of Si excess, boron concentrations, and annealing temperatures is examined with the aim of optimizing the PL efficiency and clarifying the PL mechanism. The interface region between sub-nanometer scale/nanometer-scale Si and SiO2matrix, or the atomic scale Si aggregates in SiO2matrix are most likely housing the luminescence centers which are formed by the promotion of boron and are active in white light emission properties. In particular, for moderate values of Si excess, our boron-doped silicon-rich oxide films possess both the intense white luminescence property and enhanced electroconductivity. In summary, this system has the following advantages:since all elements of the film (B, O, Si) are "CMOS periodic table" elements, the production is completely compatible with existing microelectronics technology and is of low cost; by adjusting the Si excess, boron content and annealing temperature, one can tune the white light emitting, which is a considerably simple fabrication process; the electrically activated boron doping can improve the electrical transport properties of the film, which makes it more suitable for Si-based optoelectronic integration.更多还原