纳米尺度铌酸锂的载流子输运和光电性能研究

Lithium niobate is a kind of excellent multi-functional opto-electrical artificial material and is regarded as silicon of photonics, which has various important applications on electro-optical modulation, waveguide devices, nonlinear optical frequency conversion, and so on. However, for bulk lithium niobate, it is still suffered from the bottleneck problems such as optical damage at high light intensities, slow response rate and the inefficiency and difficulty to exploit the photovoltaic effect. These problems are directly related to the charge carrier transport properties in lithium niobate, especially in the characteristics of a low conductivity due to its large bandgap, which is very difficult to be adjusted in practice. Since the mean transport length of charge carriers such as electrons and holes is typically of the order of nanometers in lithium niobate, therefore, the charge carrier transport processes in nano-scale lithium niobate are expected to be very different from those of bulk lithium niobate. This provides the possibility to solve the above bottleneck problems in bulk lithium niobate. In this project, we will study the charge carrier transport processes and electro-optical properties of nano-scale lithium niobate. Novel techniques will be developed to fabricate nano-scale structures such as stable nano-scale ferroelectric domain and domain well and nano-scale waveguides based on lithium niobate. We will study the ways to modulate the charge carrier transport behaviors in nano-scale lithium niobate, and try to enhance the electro-optical response of nano-scale lithium niobate, which will pave the way for novel potential applications of nano-scale lithium niobate in intergrated optics, nano-opto-electronics and photovoltaics.

铌酸锂晶体是一种性能优良的多功能光电材料，被称为光子学硅，在电光调制、波导器件、非线性频率变换等领域已经获得了广泛的应用。然而铌酸锂体材料仍然存在光损伤、响应速度慢以及光伏效应无法有效利用等一系列实际应用的瓶颈问题。这些问题均与铌酸锂中载流子的输运性质有关，主要体现在铌酸锂体材料的电导率极低，且禁带宽从而极难调控。鉴于铌酸锂晶体载流子输运的自由程等特征长度一般在纳米尺度，因此，纳米尺度铌酸锂结构中的载流子输运行为将迥异于铌酸锂体材料，从而有可能解决铌酸锂晶体在实际应用中的上述瓶颈问题。本项目将主要研究纳米尺度铌酸锂的载流子输运行为及其光电性质，发展制备稳定纳米畴和畴壁、纳米波导等纳米尺度铌酸锂结构的新技术，研究纳米尺度铌酸锂中载流子输运行为的调控方法，增强纳米尺度下铌酸锂的光电响应性能，从而为纳米尺度铌酸锂结构在集成光学、纳米光电子学以及光伏能源领域的新应用奠定基础。

本项目主要围绕铌酸锂纳米结构的制备、纳米尺度铌酸锂结构中的载流子输运行为及其光电性质开展研究，取得了以下系列成果：（1）发展了晶体预热处理技术，提高了铌酸锂单晶薄膜铁电畴结构的温度稳定性。利用原子力显微镜高压探针极化铌酸锂单晶薄膜，发展了两步极化技术，消除了铌酸锂单晶薄膜的反常极化效应，获得了直径约为30nm的稳定的铌酸锂点畴结构。（2）采用原子力显微镜高压探针极化技术和外电场极化技术，分别成功制备出n型head-to-head型导电畴壁和p型tail-to-tail型导电畴壁，其电导率可达10^{-6} /欧姆.厘米 - 10^{-4} /欧姆.厘米的量级，相较于铌酸锂体畴的电导率提高了至少5-6个数量级。（3）采用两步极化反转方法成功制备出了几十纳米宽度的新型n型和p型铌酸锂表面纳米畴壁结构，其电导率可达10^{-6} - 10^{-7}/欧姆.厘米的量级。（4）成功制备出周期极化铌酸锂微腔、铌酸锂啁啾光栅耦合器、掺Er铌酸锂微腔和波导等微纳结构，实现了高效的非线性频率转换、光耦合、微腔激光和波导光放大器等光电功能。. 本项目在执行期间，在Light: Sci. & Appl.、Opt. Lett.、Opt. Express、Photon. Res.、Phys. Rev. A、Adv. Sci.和Sci. China-Phys. Mech. Astron.等学术刊物共发表论文19篇，获得授权中国发明专利3项，在国内国际学术会议上做邀请报告3次。培养博士2名，硕士1名。

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