【作者】 王强；

【导师】 蒋毅坚； 闫胤洲；

【作者基本信息】 北京工业大学 ， 光学工程， 2019， 博士

【摘要】 作为第三代半导体材料的典型代表,ZnO呈现本征n型导电,其高质量的n型掺杂很容易实现,但其稳定、高效、可重复的p型掺杂却异常困难,这严重阻碍了ZnO材料在光电领域的大规模应用。制备可靠p型ZnO的关键是解决受主态的稳定性问题。围绕这一核心问题。本文提出并研究了一种生长稳定、可重复、高质量、本征富受主型ZnO(Acceptor-rich ZnO,A-ZnO)单晶微米管的方法,在此基础上,研究该种微米管的生长机理和光电特性,并进一步探索其相关应用。首先,依托光学浮区炉系统,提出光学气化过饱和析出法(Optical vapour supersaturated precipitation,OVSP)制备A-ZnO单晶微米管。研究了OVSP法生长A-ZnO单晶微米管的生长机理,发现其遵循Zn蒸汽过饱和析出生成微米棒随后轴向光热分解形成微米管的生长机理,其中均匀温度场和富氧气氛是OVSP法生长A-ZnO微米管的必要条件,也是保证所生长样品富含受主的关键因素。通过数值模拟与实验验证相结合的方法,研究了主要生长参数(加热功率、生长平台、灯丝几何形状)对生长过程中光学温度场分布的影响。结果表明:65%(1500W)的加热功率、适宜的锥形生长平台、单厚灯丝光源配置有利于在A-ZnO微米管生长区域形成均匀的光学温度场分布,有助于高质量ZnO单晶微米管的生长,且能有效防止孪生微米管现象的发生。然后,研究了A-ZnO微米管的光电特性。研究结果表明:A-ZnO微米管内含有大量受主,它主要来自价带顶127 meV处的本征锌空位缺陷,具有很高的时效性和稳定性;In/Ga合金是实现A-ZnO微米管欧姆接触的适宜电极材料。此外,利用掩模技术,将A-ZnO微米管与n型ZnO:Sn薄膜结合形成同质类p-n结器件。该器件展示了较好的整流特性,截止电压为0.72 V,开启电压为1.90 V,反向饱和电流为<10μA,反向击穿电压为>15 V。其次,通过调整生长参数,制备出壁厚为750 nm、直径为50μm的超薄壁(Ultra-thin-walled,UTW-)ZnO微米管。研究发现,UTW-ZnO微米管是一种可支持多种光学谐振模式的新型微腔。以此探索了此种新型微腔在光学领域的应用:实现了精确温度调控多彩高效荧光,即从近白色(0.30,0.39)到紫色(0.17,0.07)再到蓝紫色(0.17,0.12)的大范围调控,克服了传统ZnO材料激子及施主受主对发光峰高温下易淬灭的不足;实现了超低阈值紫外波导型光学回音壁模式的激射,阈值低至5.5μW;提出了可循环型ZnO微米管片上微流道光催化降解系统,在15分钟太阳光的照射下,微米管处高浓度亚甲基蓝溶液即被完全降解。最后,通过优化入射-微腔-探测的光学几何配置,将UTW-ZnO微米管微腔的自吸收效率从34.1%提高到77.2%,有效抑制自由激子的复合通道,提高激子间散射几率,促进自发辐射放大。此外,利用银纳米颗粒对UTW-ZnO微米管荧光的淬灭作用,计算了微腔对荧光光子的自吸收系数,并发现Purcell效应比表面等离体效应在增强荧光强度方面效率高40倍。本论文所取得结果,为今后进一步开展p型ZnO及其器件的制备研究提供了技术基础,同时也为新型半导体光学微腔设计与应用提供了新的思路。更多还原

【Abstract】 ZnO is a representative of the 3^rd generation semiconductors,its high-quality n-type doping ZnO is easy to achieve due to its intrinsic n-type conductivity.However,the fabrication of reliable p-type ZnO is a major challenge to realize ZnO-based electronic device applications.Undoubtedly,the stable acceptor is the base of reliable doped p-ZnO.In this thesis,we proposed a novel technique to grow free-standing undoped acceptor-rich ZnO（A-ZnO）microtubes with high quality,stability,and reproducibility.On this basis,the corresponding electronic and optical properties of ZnO microtubes were studied,and a series of novel applications were prepared.Firstly,the optical vapour supersaturated precipitation（OVSP）method was presented to fabricate A-ZnO microtubes based on an optical floating zone furnace.The Zn vapor supersaturated precipitation and axial photo-thermal-decomposition were proposed to interpret the microrods growth and microtubes formation,respectively.Uniform temperature field and oxygen-enriched atmosphere were found to be the necessary conditions for the growth of A-ZnO microtubes in acceptor-rich by OVSP method.The effects of major growth parameters（e.g.lamp power,filament geometry and growth platform shape）on temperature field at the growth platform of precursor rod were investigated by a finite element model as well.The lamp power of 65%（1500W）,thick single-filament and appropriate conical growth platform shape were beneficial to achieve a uniform temperature field for consistent microtubes finish-quality and prevent twinmicrotubes formation.Secondly,the optical and electric characteristics of A-ZnO microtubes were studied.The results show that A-ZnO microtubes contain abundant of stable acceptors,which originate from intrinsic zinc vacancy defects at the top of valence band of 127meV.In addition,In/Ga alloy was found to be an appropriate electrode material for A-ZnO microtubes to realize ohmic contact.On this basis,the undoped A-ZnO microtube was partially deposited by ZnO:Sn film to form a mimetic p-n homojunction,which demonstrated a rectification behaviour with the threshold voltage of 0.7 V,turn-on voltage of 2.1 V,reverse breakdown voltage>15 V,and reverse saturation current of<10μA,respectively.Then,the Ultra-thin-walled（UTW-）ZnO microtubes with a diameter of⁵0μm and a facet wall thickness of⁷50 nm were fabricated using optimized OVSP method.Spectral results show that the UTW-ZnO microtube could be used as a novel microcavity that supports various optical modes.Therefore,the optical applications on UTW-ZnO microtube were explored:（1）The temperature-controlled multicolor,free-quenching,and high-efficiency luminescence was achieved,which ranged from the visible band to near-white（0.30,0.39）then to bluish-violet（0.17,0.12）.（2）UV lasing was also realized in the single UTW-ZnO microtube under an unprecedented low threshold of 5.50μW.（3）The UTW-ZnO microtubes-based microfluidic chips was demonstrated for recyclable on-chip degradation,where high concentration methylene blue solution could be completely degraded under solar irradiation of 20 mins.Finally,the self-absorption ratio in the UTW-ZnO microtube was increased from34.1%to 77.2%by optimizing the excitation-microcavity-detection geometry.Meanwhile,the possibility of exciton-exciton collision was raised although the recombination channel for free exciton was suppressed,which could boost the low-threshold amplified spontaneous emission.Based on the quenching effect of Ag nanoparticles on photoluminescence of UTW-ZnO microtubes,the self-absorption coefficients of fluorescent photons in microcavities were calculated and analyzed.It is also found that the enhancement ratio for UV band emissions by Purcell effect in UTW-ZnO microtubes could be up to 40 folds higher than that using localized surface plasmon resonance via Ag nanoparticles.The results of this thesis not only provide technical support for the further research on the preparation of p-type ZnO and its devices,but also pave new ways for the design and application of novel semiconductor optical microcavities.更多还原