高质量单层连续二硫化钼的范德瓦尔斯外延生长研究

Monolayer molybdenum disulfide film is a new risen two dimensional materials with high band gap ~1.8eV, which is ultra-thin and tailorable for device integration and miniaturization in the next generation semiconductors. It shows great potentiality for electrical devices and photoelectrical devices with high sensitivity and low consumption. Nodoubt high-quality of continuous monolayer molybdenum disulfide film is the base for its commercial application. Currently the main problem for prototype device of monolayer molybdenum disulfide is the low carrier mobility. Besides of the not high intrinsic carrier mobility, the vacancies and domain boundaries hugely decrease its carrier mobility. The current problem is toxication of reactional source, low controllability of growth process and film discontinuity. Meanwhile, considering the large-scale application, for example the device integration, molybdenum disulfide film should be continuous. We have obtained multi-crystalline monolayer molybdenum disulfide film on molybdenum disulfide substrate by our developed three-region CVD reaction system. In this project, we will grow monolayer molybdenum disulfide film on single crystal substrates including h-BN, quartz and sapphire by our firstly developed Van Der Waals epitaxial growth system. We will systematically study the growth mechanism and growth mode of monolayer molybdenum disulfide film. And we will also explore the influence of growth parameters to the nucleation and consequence growth, and then control the growth situation with tunable crystal size and shape for the high-quality monolayer crystal molybdenum disulfide film. AFM, TEM, XPS, Raman and PL will be used to characterize the morphology, structure of the grown molybdenum disulfide film. Eventually, Monolayer molybdenum disulfide film based EFT device will be fabricated and the electrical and photoelectrical properties will be measured. This project not only provides the feasible fabrication of high-quality monolayer molybdenum disulfide film for remarkable electrical and photoelectrical properties, but also be a reference for the growth of other transition metal dichalcogenides and the heterojunction structures.

单层二硫化钼是新型二维半导体材料，具有~1.8eV禁带宽度，由于其超薄、可加工裁剪、有利于器件集成和小型化发展，是新一代理想的半导体材料。制备单层、大面积连续、高质量的二硫化钼是这种新型材料走向商业化应用之前的必要基础。目前，基于单层二硫化钼的原型器件中面临的主要问题是二硫化钼中载流子的迁移率较低。除了本征迁移率较低外，二硫化钼中缺陷空位、晶界等也是影响其载流子迁移率的主要因素。然而，由于制备过程中的反应源的中毒、可控性差等问题，生长单层高质量、大面积的连续二硫化钼薄膜在技术上还存在挑战。我们在前期研究基础上，将利用范德瓦尔斯外延生长技术来解决大面积、高质量单层连续二硫化钼薄膜生长的问题。探讨二硫化钼生长机制和生长模式、研究生长条件对二硫化钼成核和生长的影响，包括晶体寸和形状的调制，从而控制二硫化钼的成膜特性，进行单层连续二硫化钼单晶薄膜的可控生长，并构建场效应晶体管器件，研究其特性。

提出了氧气辅助化学气相沉积制备单层二硫化钼，不仅有效解决了三氧化钼源中毒的问题，而且有效地抑制了硫空位的产生，大大提高了样品质量。单层二硫化钼晶粒边长可以达到大约350微米，器件电流开关比为~10e7，室温场效应迁移率可以到达~90cm2/(V·s)。进而，采用范德瓦尔斯外延生长，在单晶衬底上可控外延制备了大面积、高质量、连续单层二硫化钼薄膜。并实现了高取向晶圆级100%覆盖单层二硫化钼薄膜的外延制备，只有0°和60°两种晶体取向。相同取向晶畴融合形成单晶，不同取向晶畴融合形成0°／60°晶界；具有直接带隙为2.11 eV，观察到价带顶劈裂为140 meV。基于外延膜转移到 二氧化硅衬底上制备的晶圆规模器件阵列具有良好的性能，本征场效应晶体管器件为n型，平均沟道迁移率为40 cm2V-1s-1。在单层二硫化钼的低成本、高效、晶圆级外延生长上取得突破，这一方法具有普适性，适用于不同衬底上二硫化钼的生长，甚至可以推广到其它过渡金属硫属化物的生长。同时还开发了一种简单、无污染、快速、非破坏性的二硫化钼转移方法, 利用水辅助能够将晶圆级二硫化钼薄膜从蓝宝石转移到其他任意衬底上。在转移之后, 这些蓝宝石晶片仍可用于后续的生长。这种转移技术还能够应用于层数和角度控制的复杂堆叠结构。